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Abstract Wind, a major source of environmental noise, forces invertebrates that communicate with plant-borne vibrations to adjust their signaling when communicating in windy conditions. However, the strategies that animals use to reduce the impact of wind noise on communication are not well studied. We investigated the effects of wind on the production of tremulatory signals in the neotropical katydid Copiphora brevirostris. First, we recorded katydid signaling activity and natural wind variation in the field. Additionally, we exposed katydid couples during their most active signaling time period to artificial wind of different levels, and we recorded the number of tremulations produced by the males. We found that wind levels are at their lowest between 2:00 and 5:00 in the morning, which coincides with peak signaling period for male katydids. Furthermore, we found that males produce significantly fewer tremulations when exposed to wind rather than acoustic noise or silence. Wind velocity significantly affected the number of tremulations produced during the wind treatment, with fewer tremulations produced with higher wind velocities. Our results show that katydids can time their vibratory signaling both in the short- and long-term to favorable sensory conditions, either through behavioral flexibility in response to short-term fluctuations in wind or as a result of an evolutionary process in response to predictable periods of low-wind conditions. Significance statement Animal communication can be hampered by noise across all sensory modalities. Most research on the effects of noise and the strategies to cope with it has focused on animals that use airborne sounds to communicate. However, although hundreds of thousands of invertebrates communicate with vibrational signals, we know very little about how noise affects this form of communication. For animals that rely on substrate-borne vibrations, wind represents the major source of environmental noise. Wind velocity levels can be predictable at a long-term scale (hours) but rather unpredictable at a short time scale (seconds). Both scales of variation are important for communication. Using a combination of field observations and lab experiments, we investigated the strategies used by a neotropical katydid Copiphora brevirostris to cope with vibrational noise induced by wind. Our results demonstrate that C. brevirostris times its signals at the long- and short-term range. Katydids signaled more at the times at night when wind velocity was lowest. Moreover, when exposed to wind gusts during their peak time of activity, katydids signaled more during the wind-free gaps.

Abstract Key social traits, like queen number in eusocial insect colonies, have long been considered plastic, but the recent finding that colony social organization is under strict genetic control in multiple ant lineages challenges this view. This begs the question of which hardwired behavioral mechanism(s) generate alternative forms of social organization during colony development. We addressed this question in the Alpine silver ant, Formica selysi, a species with two social forms determined by a supergene. Queens that carry exclusively the M haplotype are produced by and live in monogyne (= single-queen) colonies, whereas queens that carry at least one copy of the P haplotype are produced by and live in polygyne (= multiple-queen) colonies. With extensive field samplings and laboratory experiments, we show that both types of queens successfully establish colonies independently, without being accompanied by workers, but that they do so in contrasting ways. Monogyne queens were generally intolerant of other queens and founded colonies solitarily, whereas polygyne queens were mutually attracted to each other and mainly founded colonies cooperatively. These associations persisted for months after worker emergence, suggesting that cooperative colony-founding leads to permanent multiple queening. Overall, our study shows that queens of each social form found colonies independently in the field but that P-carrying queens are more likely to cooperate, thereby contributing to perpetuate alternative forms of social organization. Significance statement Understanding the genetic and behavioral underpinnings of social organization is a major goal in evolutionary biology. Recent studies have shown that colony social organization is controlled by supergenes in multiple ant lineages. But the behavioral processes linking the genotype of a queen to the type of colony she will form remain largely unknown. Here, we show that in Alpine silver ants, alternative supergene genotypes are associated with different levels of social attraction and tolerance in young queens. These hardwired differences in social traits make queens carrying the P supergene haplotype more prone to cooperate and form durable associations during independent colony-founding. These findings help explain how genetic variants induce alternative forms of social organization during the ontogeny of a colony. They also illustrate how simple phenotypic differences at the individual level can result in large differences at higher levels of organization.

Animal movement modeling and animal personality frameworks are both useful approaches to identify patterns of behavioral variation. Yet these approaches are seldom applied jointly, especially in the context of a controlled laboratory experiment. In this study, we combine these approaches to identify patterns in the behavior of neonate snakes at different time scales (within several minutes of a trial and across the days of the experiment). Specifically, we utilize Bayesian hierarchical hidden Markov models on fine-scale movement data and Bayesian mixed linear models on additional behavioral data (average movement speed, tongue-flick rate, latency to emerge, and area explored) measured repeatedly in captive-born western terrestrial garter snakes (Thamnophis elegans). This novel approach identified distinct behavioral states that describe movement patterns and predictable patterns of transitions in behavioral states at different time scales. Snakes exhibited consistent among-individual variation for all traits, and behaviors were correlated across contexts. Patterns of behavioral changes over time demonstrate responsiveness consistent with habituation, a basic form of learning, but snakes did not learn to associate a novel object with a simulated attack. Our unique approach provides a useful case study in how the joint application of statistical methodologies often relegated to different fields can be leveraged to describe personality axes and to characterize shifts in behavior at short (minutes) and long (across days) time scales in an experimental design context. Using a combination of traditional statistical approaches and novel movement modeling, we identified patterns in the behavior of baby snakes at different time scales (within several minutes of a trial and across the days of the experiment). Snakes were consistent in their behaviors and exhibited individual differences in these behaviors. Further, behaviors were correlated across contexts: snakes that were more active in an open field test were also more likely to emerge from a hide and explore. Over time, snakes decreased their responsiveness to repeated stimuli, which suggests a basic form of learning. However, we found no evidence that snakes could learn to associate a novel object with a simulated attack within the timeframe of our experiment.

Polygyny is the most common mating system in mammals, and many species form uni-male multi-female groups (UM-MF units). Polygynous systems are traditionally distinguished according to male reproductive strategies, such as “resource defense” or “female defense,” both of which are often described in the literature as forming “harems.” However, this focus on male strategies, and the use of umbrella terms to describe them, lumps together societies that fundamentally differ in their ontogeny, stability, and relationships. Integrating foundational theories of mating strategies with the principles governing relationship dynamics, driven by both male and female strategies and modulated by male-female conflicts of interest, we propose a new framework for classifying the diversity of UM-MF units. We differentiate UM-MF groups in terms of average female kinship within the group and length of male tenure to define general classes with distinct predictions for the nature of inter- and intrasexual relationships. We propose a narrower definition for the “true harem” along with new terminology to describe the other three classes: “benign consortship,” “coterie,” and “coercive consortship.” Using socioecological data for 40 mammalian species from 27 families, we found our framework was able to successfully predict patterns of female-female cooperation and the presence of coercive male-female relationships. Finally, we refine our framework, identifying subclasses of the main four classes and propose hypotheses about the underlying causes of observed patterns. By focusing on the nature of within group relationships, this framework provides a powerful lens for asking broad, comparative evolutionary questions about social evolution and socioecology.

Nest-dwelling ectoparasites are a major source of stress for growing nestling birds, as they can negatively impact on growth and physiology, with consequences on pre-fledging mortality. Ectoparasites are expected to also affect chromatic traits involved in parent-offspring communication, because their expression requires the same resources used by nestlings for parasites defence and/or it is linked to individual state. However, the effects of ectoparasites on growth, condition and expression of begging components are poorly known, especially in raptors. Here, we examined the effects of an experimental ectoparasites removal on growth (body mass and forearm length) and expression of begging traits (size and colour of flange, cere and gape) in lesser kestrel (Falco naumanni) nestlings. Our manipulation was very effective in removing ectoparasites and parasite load had several detrimental effects on early growth and expression of visual signals directed to parents. Deparasitized nestlings grew faster in terms of body mass and forearm length, as well as mouth width and cere length. In addition, the red chromaticity of cere decreased with age, with deparasitized nestlings showing a faster decrease concomitantly with the increase in body growth. Such negative effects disappeared in later nestling stages and ectoparasites did not affect pre-fledging survival. Our results showed that visual components of begging have the potential to reveal individual condition during early nestling stages, above and beyond ectoparasite infection. They are also consistent with previous evidence that ectoparasites weakly affect fitness in colonial and cavity-nesting avian hosts, which have evolved greater resistance due to prolonged host-parasite interactions. Ectoparasites are considered a major stressor for nestling birds, as they can negatively affect their growth, survival but also traits involved in parent-offspring communication. We experimentally show that ectoparasite infection has only little and transient negative effects on the early growth of lesser kestrel nestlings. However, nestlings recover from such a slower growth without paying any cost in terms of final body size and pre-fledging survival. In addition, we reveal that mouth colour does not mirror the level of ectoparasite infestation, but it is a reliable signal of nestlings’ individual general condition. Therefore, ectoparasites only weakly affect fitness in this species, likely because of the intense host-parasite interaction, which is typical of colonial and cavity-nesting species.

Social behavior can have a major impact on the dynamics of infectious disease outbreaks. For animals that live in dense social groups, such as the eusocial insects, pathogens pose an especially large risk because frequent contacts among individuals can allow rapid spread within colonies. While there has been a large body of work examining adaptations to mitigate the spread of infectious disease within social insect colonies, there has been less work on strategies to prevent the introduction of pathogens into colonies in the first place. We develop an agent-based model to examine the effect of territorial behavior on the transmission of infectious diseases between social insect colonies. We find that by preventing the introduction of infected foreign workers into a colony, territoriality can flatten the curve of an epidemic, delaying the introduction of an infectious disease and reducing its maximum prevalence, but only for diseases with moderate to low transmissibility. Our results have implications for understanding how pathogen risk influences the evolution of territorial behavior in social insects and other highly social animals. Significance statement Infectious disease outbreaks can impose a large fitness cost to animals that live in social groups. The frequency and pattern of contacts both within and among groups can have a large impact on the speed and extent of an epidemic. Using an individual-based model, we examined how the exclusion of foreign workers from a territory around the nest influences disease transmission between social insect colonies. We find that territoriality can protect colonies from outbreaks of low to moderately contagious pathogens by delaying the spillover from other colonies and reducing the maximum number of workers who are infected. These results suggest that the relative threat posed by infectious diseases may have played an important role in shaping the diversity of territorial behaviors seen in different social insect species. Supplementary Information The online version contains supplementary material available at 10.1007/s00265-021-03095-0.

Abstract Urbanisation is a globally occurring phenomenon and is predicted to continue increasing rapidly. Urban ecosystems present novel environments and challenges which species must acclimate or adapt to. These novel challenges alter existing or create new selection pressures on behaviours which provide an opportunity to investigate eco-evolutionary responses to contemporary environmental change. We used 7 years of breeding data from urban and forest populations of blue and great tits to understand whether selection for timing of breeding or clutch size differed between the two habitats and species. We found that urban great tits laid eggs earlier than their forest counterparts, but there was no evidence of a difference in selection for earlier breeding. Blue tits, however, did not differ in timing of egg laying between the two habitats, but selection for earlier laying was weaker in the urban environment. Both species laid smaller clutches in the urban site and had positive selection for larger clutch sizes which did not differ in strength for the great tits but did for blue tits, with weaker selection in the urban population. Our results suggest that food availability for nestlings may be constraining urban birds, and that the temporal cues females use to time breeding correctly, such as tree budburst and food availability, may be absent or reduced in urban areas due to lower caterpillar availability. These results have implications for our understanding of the adaptation of wild animals to city life. Significance statement Urbanisation is expanding rapidly and changing the environment many species live in. A key challenge is to understand how species adapt to the urban environment, why some species can adapt, why others cannot and what we can do to ensure that cities are ecologically sustainable and biodiversity rich. Here we show that the strength of natural selection for early breeding and larger clutch size is weaker in urban than non-urban blue tits, likely due to reduced and irregular availability of natural insect food in urban areas. This effect was not found in great tits. Thus, urbanisation can alter the selection pressures wild animals are exposed to, but this effect may differ between species, even when closely related. This has implications for our understanding of how species adapt to urban life.

Abstract Populations of migratory bird species have suffered a sustained and severe decline for several decades. Contrary to non-migratory species, understanding the causal mechanisms proves difficult (for migratory bird species) as underlying processes may operate across broad geographic ranges and stages of the annual cycle. Therefore, the identification of migration routes, wintering grounds, and stopover sites is crucial for the development of relevant conservation strategies for declining migrant bird species. We still lack fundamental data of the non-breeding movements for many migratory species, such as European turtle doves Streptopelia turtur, a trans-Saharan migrant. For this species, knowledge of non-breeding movements is mainly based on ringing data that are limited by a low recovery rate in Africa, and tracking studies with a strong bias towards individuals breeding in France. We used Argos satellite transmitters to obtain detailed year-round tracks and provide new insights on migration strategies and winter quarters, of turtle doves breeding in Central and Eastern Europe. The tracking data along with analysis of land cover data confirm previously assumed use of multiple wintering sites and the use of a wide range of forest and agricultural landscapes at the breeding grounds. Tracking data in combination with environmental parameters demonstrated that most environmental parameters and niche breadth differed between breeding and wintering grounds. “Niche tracking” was only observed regarding night-time temperatures. Furthermore, we provide evidence for breeding site fidelity of adult individuals and for home range size to increase with an increasing proportion of agricultural used areas. Significance statement The European turtle dove, a Palearctic-African migrant species, is one of the fastest declining birds in Europe. The rapid decline is presumed to be caused mainly by habitat modification and agricultural changes. Here, we represent data on migration strategies, flyways, and behavior on European breeding and African non-breeding sites of turtle doves breeding in Central and Eastern Europe equipped with satellite transmitters. Our results confirm the use of different migration flyways and reveal an indication for “niche switching” behavior in terms of environmental factors during the different annual phases. The migratory behaviors revealed by the tracking approach, e.g., prolonged stopovers during autumn migration in Europe overlapping with time of hunting activities, stopovers in North Africa during spring migration, or evidence for loop migration, are important protection-relevant findings, particularly for the Central-Eastern flyway, for which no tracking data has been analyzed prior to our study.

Social interactions with conspecifics are key to the fitness of most animals and, through the transmission opportunities they provide, are also key to the fitness of their parasites. As a result, research to date has largely focused on the role of host social behavior in imposing selection on parasites, particularly their virulence and transmission phenotypes. However, host social behavior also influences the distribution of parasites among hosts, with implications for their evolution through non-random mating, gene flow, and genetic drift, and thus ability to respond to that selection. Here, we review the paucity of empirical studies on parasites, and draw from empirical studies of free-living organisms and population genetic theory to propose several mechanisms by which host social behavior potentially drives parasite evolution through these less-well studied mechanisms. We focus on the guppy host and Gyrodactylus (Monogenea) ectoparasitic flatworm system and follow a spatially hierarchical outline to highlight that social behavior varies between individuals, and between host populations across the landscape, generating a mosaic of ecological and evolutionary outcomes for their infecting parasites. We argue that the guppy-Gyrodactylus system presents a unique opportunity to address this fundamental knowledge gap in our understanding of the connection between host social behavior and parasite evolution. Individual differences in host social behavior generates fine-scale changes in the spatial distribution of parasite genotypes, shape the size, and diversity of their infecting parasite populations and may generate non-random mating on, and non-random transmission between hosts. While at population and metapopulation level, variation in host social behavior interacts with landscape structure to affect parasite gene flow, effective population size, and genetic drift to alter the coevolutionary potential of local adaptation. Social interactions between animals shape the evolution of the pathogens that infect them. Most research exploring this phenomenon has focused on the selection such interactions impose, but social hosts also shape parasite evolution by determining the ability of their parasites to respond to that selection. Here, we explore how host social behavior drives parasite evolution by shaping non-random mating, gene flow, and genetic drift, from the scale of the individual to the landscape. The relative strength of these evolutionary mechanisms can have striking implications for the evolution of parasite traits such as virulence and alter the evolutionary trajectories of populations across the landscape. We emphasize the importance of studies combining parasite population genetics, host social behavior, and landscape processes to illuminate complex host-parasite coevolutionary dynamics.

Aquatic prey can gauge predation risk using chemical information, including chemical alarm cues — released when prey are injured, disturbance cues — released when prey are threatened, or the odour of the predator itself. While a lot of work has focused on alarm cues, disturbance cues remained poorly studied in freshwater systems, and has been virtually omitted in marine ones. In the current study, we document the first evidence of disturbance cue use in a marine fish. Juvenile damselfish Pomacentrus nagasakiensis were exposed to cues from undisturbed or disturbed conspecifics, a water control (negative control) and conspecific alarm cues (positive control). Juveniles displayed increased antipredator responses when exposed to alarm cues and disturbed conspecifics, but not when exposed to undisturbed ones. In addition, we demonstrated that disturbance cues, just like alarm cues, could mediate learned predator recognition, a phenomenon undemonstrated in freshwater fishes. Given disturbance cues are thought to be comprised of nitrogenous waste, it has been hypothesised that the constant and dilute release of such products in the hypotonic freshwater environment results in a high level of ‘background chemical’ noise masking subsequent releases. Extending this hypothesis, we propose that in the marine environment, disturbance cues are more easily detected due to low background noise. Prey animals must accurately assess their current predation risk. Aquatic prey rely on chemical cues to gain information on risk. These cues can include odours released when nearby prey are damaged or disturbed, or the odour of a known predator. Prey exposed to a novel odour for the first time must learn if the odour is an indication of risk or benign. This is accomplished when the odour of a known risk (e.g. cues released from a damaged individual) is paired with a novel odour (e.g. a novel predator). In the current paper, we show for the first time that coral reef fishes can use disturbance cues (cues released when prey are chased or otherwise disturbed) as a ‘known risk’ and when paired with a novel odour, are subsequently able to respond to the novel odour when presented alone.

Abstract A key benefit of sociality is a reduction in predation risk. Cohesive group behaviour and rapid collective decision making are essential for reducing predation risk in groups. Parasite infection might reduce an individuals’ grouping behaviours and thereby change the behaviour of the group as a whole. To investigate the relationship between parasite infection and grouping behaviours, we studied groups of three-spined sticklebacks, Gasterosteus aculeatus, varying the number of individuals experimentally infected with the cestode Schistocephalus solidus. We studied groups of six sticklebacks containing 0, 2, 3, 4 or 6 infected individuals before and after a simulated bird attack. We predicted that infected individuals would have reduced shoaling and swimming speed and that the presence of infected individuals within a group would reduce group cohesion and speed. Uninfected fish increased shoaling and reduced swimming speed more than infected fish after the bird attack. In groups containing both infected and uninfected fish, the group behaviours were dominated by the more frequent character (uninfected versus infected). Interestingly, groups with equal numbers of uninfected and infected fish showed the least shoaling and had the lowest swimming speeds, suggesting that these groups failed to generate a majority and therefore displayed signs of indecisiveness by reducing their swimming speed the most. Our results provide evidence for a negative effect of infection on a group’s shoaling behaviour, thereby potentially deteriorating collective decision making. The presence of infected individuals might thus have far-reaching consequences in natural populations under predation risk. Significance statement Parasite-infected individuals often show deviating group behaviours. This might reduce the anti-predator benefits of group living. However, it is unknown whether such deviations in group behaviour might influence the shoaling behaviour of uninfected group members and thereby the behaviour of the group as a whole. By experimentally infecting sticklebacks and investigating groups varying in infection rates, we show that infected sticklebacks differ in their shoaling behaviours from uninfected sticklebacks. Additionally, the presence of infected sticklebacks within the group affected the behaviour of uninfected shoal members. We show that shoals of infected fish are less cohesive and move slower compared to shoals of uninfected fish. Furthermore, we show that the infection rate of the shoal is crucial for how the group behaves.

Social thermoregulation is the huddling of two or more individuals that share endogenous warmth to reduce thermoregulation costs. Strategies vary widely depending on the species’ social behavior and the ambient ecological conditions. In greater white-toothed shrews (Crocidura russula), huddling is employed in communal nests only in the colder months, which suggests that temperature is an important factor in the species’ social thermoregulation strategy. To test this hypothesis, we analyzed the behavior and physiology of five groups of shrews from winter, acclimated to 14 °C, and four groups from summer, acclimated to 24 °C. Each group consisted of six captive males that were first housed singly for 2 days and later allowed to interact with other shrews of the same group. Our analysis revealed all group mates were frequently found huddling in the same shelter, regardless of acclimation temperature. However, mass-adjusted resting metabolic rate decreased in winter shrews with larger huddle sizes and remained constant in summer shrews in huddles with three or more individuals. Body temperature was also significantly lower and more varied in winter shrews. After being group-housed, winter shrews used less torpor and significantly increased their body mass and food intake in the first days. Our results suggest that temperature had a small influence in huddling behavior but a large one in physiological factors, such as metabolism, body temperature, and food intake, after shrews started interacting socially. Therefore, social thermoregulation provides benefits to C. russula besides energy savings. Small mammals often huddle to reduce thermoregulation costs during cold. Previous studies in wild greater white-toothed shrews suggested that this species only employs social thermoregulation in the colder months of the year. We captured wild shrews and assessed the energetic advantages of this social thermoregulation strategy under controlled conditions. We confirmed that social thermoregulation indeed has more energetic benefits to shrews in winter than in summer. However, huddling between individuals still occurs at warm temperatures, when energetic benefits are no longer significant. Such observations suggest that huddling is advantageous to shrews in multiple ways beyond thermoregulation. Furthermore, social interaction between individuals influenced daily torpor, body mass, and feeding, further supporting the hypothesis that sociality in greater white-toothed shrews has direct and indirect effects on their energy budget.

Inbreeding depression is commonly considered an evolutionary influence on pre-copulatory mechanisms of inbreeding avoidance. Inbreeding may be minimized by: (1) delayed maturation and reproduction, (2) sex-biased dispersal, (3) behavioural avoidance of mating with relatives, and/or (4) mating by females with multiple males (polyandry). Time constraints on reproduction and limited opportunities for outbred matings may limit mate choice, forcing females to mate with relatives and favouring multiple paternity to reduce the costs of inbred matings. Using parentage, relatedness, and spatial genetic analyses, we studied genetic mating system, dispersal and inbreeding patterns in a wild partially isolated colony of the yellow ground squirrels (Spermophilus fulvus), fast-living hibernators. Females were phylopatric, while males dispersed within the colony. Nevertheless, male-biased dispersal could not completely separate closely related males and females, and the potential risk of inbreeding was high, in particular due to early maturation of males — some of them matured before dispersal. Females did not mate assortatively with respect to relatedness of males, mating both with close kin and non-kin, and 38% of sire-mother pairs were closely related (coefficient of relatedness > 0.125). Multiple paternity was common (56% of all litters), and multiply sired litters combined offspring from inbred and outbred matings. Parents of singly sired litters were mostly unrelated. The overall level of inbreeding was low. We conclude that, under strong time constraints on reproduction and mate choice, females do not mate selectively with unrelated males. However, multiple paternity dilutes inbred matings effectively enough to maintain the overall low level of inbreeding. Models predict that inbreeding should be more common in nature than is observed. Time constraints on reproduction and low availability of mates should make females tolerant of inbreeding, while multiple mating partners of females can help them reduce its costs. Based on observations in a free-living colony of the yellow ground squirrel, Spermophilus fulvus, a hibernator with a fast pace of life, we report high rates of inbred matings in females who have limited mate choice and face severe time constraints on reproduction. However, multiple paternity observed in more than half of females reduced the average relatedness between partners and, therefore, among their offspring, resulting in the overall low inbreeding within the colony. This is a new evidence for inbreeding tolerance under limited mate choice and female polyandry as a bet-hedging strategy against inbreeding.

Crested auklets (Aethia cristatella) are colonial seabirds with brilliant orange bills during the breeding season. We characterized the bill pigment with spectroscopy methods (resonance Raman, fluorescence, absorbance). We excluded carotenoids as a possible chromophore and showed that the pigment most closely resembles pterins. Like pterins, the bill pigment fluoresces, and it occurred in two phenotypes that may differ geographically, perhaps due to environmental heterogeneity. The pigment is unique in the genus Aethia, and its spectra did not match any known molecule. The UV–Vis absorbance spectrum of the bill pigment overlaps with the extracted pigment of euphausiids, a favored food of crested auklets. A color preference associated with prey may have favored characteristics of the crested auklet’s accessory bill plates. Crest size, a signal of dominance, tended to correlate positively with the highest fluorescence in the single-band phenotype. Brighter bills may function in self-advertisement and verify the status signal of the crest ornament. We tested for a behavioral preference using identical decoys that differed only in bill fluorescence. Crested auklets approached models with fluorescent bills at a higher frequency. In cases where the sex of crested auklets was known, males responded at a higher frequency to fluorescent bills, but females did not. In an evolutionary context, bill fluorescence could have conferred an advantage in social interactions, e.g., in dimly lit rock crevices. Bill brightness and color may communicate success in foraging and may function as an honest signal of mate quality. Preferences embedded in sensory systems may influence the evolution of ornamental traits. Overlap in chemical properties of zooplankton and brilliant orange bills suggests that crested auklets prefer a bill pigment patterned on a food preference. The pigment is unique in its genus, but occurs in two fluorescent phenotypes that may vary geographically, possibly due to environmental heterogeneity. The pigment resembles a class of compounds known as pterins but could be novel. Rictal plates are bill plates that flare out from the corners of the mouth, and they tend to be brighter in crested auklets with larger feather crests. Birds with larger crests are more attractive and dominant. Brighter bills may advertise foraging success and verify status. Bill fluorescence is attractive to crested auklets. Crested auklets approached decoys with fluorescent bills at a higher frequency.

Abstract Maternal effects mediated by nutrients or specific endocrine states of the mother can affect infant development. Specifically, pre- and postnatal maternal stress associated with elevated glucocorticoid (GC) output is known to influence the phenotype of the offspring, including their physical and behavioral development. These developmental processes, however, remain relatively poorly studied in wild vertebrates, including primates with their relatively slow life histories. Here, we investigated the effects of maternal stress, assessed by fecal glucocorticoid output, on infant development in wild Verreaux’s sifakas (Propithecus verreauxi), a group-living Malagasy primate. In a first step, we investigated factors predicting maternal fecal glucocorticoid metabolite (fGCM) concentrations, how they impact infants’ physical and behavioral development during the first 6 months of postnatal life as well as early survival during the first 1.5 years of postnatal life. We collected fecal samples of mothers for hormone assays and behavioral data of 12 infants from two birth cohorts, for which we also assessed growth rates. Maternal fGCM concentrations were higher during the late prenatal but lower during the postnatal period compared to the early/mid prenatal period and were higher during periods of low rainfall. Infants of mothers with higher prenatal fGCM concentrations exhibited faster growth rates and were more explorative in terms of independent foraging and play. Infants of mothers with high pre- and postnatal fGCM concentrations were carried less and spent more time in nipple contact. Time mothers spent carrying infants predicted infant survival: infants that were more carried had lower survival, suggesting that they were likely in poorer condition and had to be cared for longer. Thus, the physical and behavioral development of these young primates were impacted by variation in maternal fGCM concentrations during the first 6 months of their lives, presumably as an adaptive response to living in a highly seasonal, but unpredictable environment. Significance statement The early development of infants can be impacted by variation in maternal condition. These maternal effects can be mediated by maternal stress (glucocorticoid hormones) and are known to have downstream consequences for behavior, physiology, survival, and reproductive success well into adulthood. However, the direction of the effects of maternal physiological GC output on offspring development is highly variable, even within the same species. We contribute comparative data on maternal stress effects on infant development in a Critically Endangered primate from Madagascar. We describe variation in maternal glucocorticoid output as a function of ecological and reproductive factors and show that patterns of infant growth, behavioral development, and early survival are predicted by maternal glucocorticoids. Our study demonstrates how mothers can influence offspring fitness in response to challenging environmental conditions.

Abstract Tadpoles can respond to perceived predation risk by adjusting their life history, morphology, and behavior in an adaptive way. Adaptive phenotypic plasticity can evolve by natural selection only if there is variation in reaction norms and if this variation is, at least in part, heritable. To provide insights into the evolution of adaptive phenotypic plasticity, we analyzed the environmental and parental components of variation in predator-induced life history (age and size at metamorphosis), morphology (tail depth), and behavior of Italian treefrog tadpoles (Hyla intermedia). Using an incomplete factorial design, we raised tadpoles either with or without caged predators (dragonfly larvae, gen. Aeshna) and, successively, we tested them in experimental arenas either with or without caged predators. Results provided strong evidence for an environmental effect on all three sets of characters. Tadpoles raised with caged predators (dragonfly larvae, gen. Aeshna) metamorphosed earlier (but at a similar body size) and developed deeper tails than their fullsib siblings raised without predators. In the experimental arenas, all tadpoles, independent of their experience, flexibly changed their activity and position, depending on whether the cage was empty or contained the predator. Tadpoles of the two experimental groups, however, showed different responses: those raised with predators were always less active than their predator-naive siblings and differences slightly increased in the presence of predators. Besides this strong environmental component of phenotypic variation, results provided evidence also for parental and parental-by-environment effects, which were strong on life-history, but weak on morphology and behavior. Interestingly, additive parental effects were explained mainly by dams. This supports the hypothesis that phenotypic plasticity might mainly depend on maternal effects and that it might be the expression of condition-dependent mechanisms. Significance statement Animals, by plastically adjusting their phenotypes to the local environments, can often sensibly improve their chances of survival, suggesting the hypothesis that phenotypic plasticity evolved by natural selection. We test this hypothesis in the Italian treefrog tadpoles, by investigating the heritable variation in the plastic response to predators (dragonfly larvae). Using an incomplete factorial common-garden experiment, we showed that tadpoles raised with predators metamorphosed earlier (but at similar body size), developed deeper tails, and were less active than their siblings raised without predators. The plastic response varied among families, but variation showed a stronger maternal than paternal component. This suggests that plasticity might largely depend on epigenetic factors and be the expression of condition-dependent mechanisms.

As animals develop, their capacities to sense cues, assess threats, and perform actions change, as do the relative costs and benefits that underlie behavioural decisions. We presented ambiguous cues to test if hatching decisions of red-eyed treefrogs, Agalychnis callidryas, change developmentally following adaptive predictions based on changing costs of decision errors. These arboreal embryos hatch prematurely to escape from egg predators, cued by vibrations in attacks. Young embryos modulate hatching based on the frequency and temporal properties of cues, reducing false alarms that unnecessarily expose them to risk in the water. Since the cost of false alarms decreases developmentally, we hypothesized that hatching responses to ambiguous cues would increase. We tested this using vibration playbacks at two ages, with two sets of 3 stimuli. We matched sampling costs and varied ambiguity in either temporal or frequency properties, so one stimulus elicited high hatching (positive control) and two elicited low hatching but differed in ambiguity, based on prior results with younger embryos. Older embryos hatched faster, indicating reduced cue sampling. They responded strongly to both clear threat cues and ambiguous stimuli but little when either property clearly indicated low risk. In both experiments, we saw the greatest ontogenetic change in response to the more ambiguous stimulus. These playback experiments improve our understanding of how embryos facing risk tradeoffs make adaptive decisions based on incidental cues from predators. Ambiguity in incidental cues is ubiquitous and developmental changes in behaviour due to ontogenetic adaptation of decision processes are likely to be widespread. Animals must use imperfect information to guide their behavior, and the costs of decision errors often change with development. We found the decision rules that embryos apply to ambiguous cues to deploy escape behavior change developmentally, matching adaptive predictions based on changing cost–benefit tradeoffs. Our results, consistent across two different forms of ambiguity, suggest selection has shaped behavioral development to improve how embryos use ambiguous incidental cues for defense. This work both extends and generalizes earlier experiments varying the cost of information. It cautions against oversimplifying assumptions about embryo information use—at least for species and in contexts where a history of strong selective tradeoffs may have honed their capacity to make a key decision well—and demonstrates the value of vibration playbacks and embryo hatching behavior for research in animal cognition.

Size-assortative mating is a pattern of non-random pairing among individuals that has been presumed to arise due to the enhanced reproductive success that may accrue from mating with an individual of similar size. Its proximal mechanism may be female choice for similarly sized mates and/or large-male advantage during bouts of direct male-male competition. The hallmark for the occurrence of size-assortative mating is a significant correlation between female and male body sizes in mated pairs. In this study, we investigated the mating pattern of the emerald glass frog, Espadarana prosoblepon, whose mating system is purportedly based on female choice and therefore is a suitable study system for testing hypotheses of size-assortative mating. We specifically tested whether E. prosoblepon males found in amplexus were larger than solitary males, indicating a large-male advantage in mating and whether either larger males or size-matched pairs of frogs had a higher proportion of their eggs fertilized, consistent with a benefit to size-assortative mating. We found no evidence for any of these relationships in E. prosoblepon despite a positive correlation between female size and clutch size. Males in amplexus were not larger than unmated males, and male size did not predict the proportion of fertilized eggs. Our evidence thus indicates that the mating pattern of E. prosoblepon is random with respect to body size, in conformity with a growing body of evidence that body size is likely not a significant factor influencing mating patterns in anurans. Size-assortative mating occurs when similarly sized individuals mate together more often than expected by chance. Studies addressing this question test for a correlation between female and male sizes within mating pairs, but few studies test whether mating with similarly sized individuals provides proximate benefits. Size-assortative mating should occur in species where mate choice is possible to occur, in which individuals can discriminate and choose to mate with similarly sized individuals. In frogs, many previous studies have searched for size-assortative mating, but evidence for its occurrence or selective advantage remains scant. We used the emerald glass frog, Espadarana prosoblepon, as a study system to test the predictions of size-assortative mating. We found that both mating preference and fertilization success are random with respect to body size.

Widespread recognition of the contribution of individual differences in behavioral phenotype to evolutionary processes raises questions as to their developmental origin: when and in what contexts such differences emerge and what aspects of the developmental environment contribute to these? We studied individual differences among littermates of the domestic cat Felis silvestris catus when competing for meat at weaning, a challenging period in mammalian development. During postnatal weeks six, seven, and eight, we tested 67 weanling kittens (40 males, 27 females) from 16 litters of mixed breed cats maintained as part of a free-ranging breeding colony. Twice a week, we tested the kittens’ behavior after they were food deprived and presented together with their siblings for 2 min with a highly palatable food, a piece of raw beef. We found stable individual differences among littermates across 3 weeks of testing in latency to reach the meat, time spent eating from it, time spent monopolizing it, and number of aggressive behaviors directed toward littermates. There was no effect of sex on any of the behavioral measures. However, kittens with lower body mass at birth (and then also lower body mass at the age of testing) relative to their littermates competed more vigorously and successfully for the meat than their heavier siblings. This suggests the importance of motivational factors arising during early development in shaping individual differences in behavior such as among littermates in the present study, when competing for a biologically relevant resource. In polytocous mammals, body mass at birth is a good predictor of growth and survival, with heavier young relative to their littermates usually obtaining a greater share of resources such as the mother’s milk. It is therefore often assumed that this advantage will translate into differences in behavior in other contexts, such that heavier littermates will gain more resources at later life stages by showing a more aggressive, “dominant” behavioral style. The findings of the present study challenge this view by demonstrating that in the domestic cat, lighter littermates were more competitive in obtaining meat at weaning. We suggest that differences in the motivational state of individuals should also be considered when accounting for the early development of individual differences in behavior, including among littermates, and may contribute to what might be broadly considered an individual’s personality or behavioral style.

Individuals within animal societies are expected to mitigate the costs and enhance the benefits associated with group living. For example, sociality can facilitate the sharing of beneficial microbes among individuals, but can also increase transmission of pathogens, representing a major cost of group living. We examined the costs of sociality in the California slender salamander (Batrachoseps attenuatus), a terrestrial salamander which naturally forms close social aggregations. We investigated whether innate sociality (e.g., skin-to-skin contact) increases an individual’s transmission risk of Batrachochytrium dendrobatidis (Bd), a fungal pathogen that emerged throughout the salamander’s range over the last 50 years and has decimated hundreds of amphibian species globally. We found that in captivity, B. attenuatus exhibit random mixing within social groups, resulting in high contact rates and high potential for Bd transmission. Our experimental infection trials resulted in 50% mortality after 1 month in moist conditions. In order to test how group size affects pathogen transmission, we manipulated social group size and found a marked effect on the spread Bd among individuals; a single, uninfected individual contracted Bd much more rapidly in larger groups of infected individuals. Surprisingly, this did not translate into a more rapid death rate or higher pathogen infection loads. Our results show that the innate behavior of group formation represents a per-individual risk of socially acquired pathogens, with direct transmission being magnified in larger social groups. This study highlights one important cost of sociality in terrestrial salamanders and underscores the general susceptibility of social animals to novel invasive pathogens. Social behaviors typically evolve due to the benefits of associating with others, but they can also present risks such as disease transmission. The California slender salamander is highly social, with individuals forming close aggregations underneath cover items. Populations of this species have recently been discovered to suffer from the widespread and deadly fungal pathogen Batrachochytrium dendrobatidis (Bd) which is transmitted through aquatic zoospores. Because this salamander host species is fully terrestrial, we set out to determine if close aggregations (leading to skin-to-skin contact) provide opportunities for direct transmission of Bd. Infection trials in larger social groups revealed a more rapid spread of Bd; however, we did not witness more rapid death rates or ultimately higher pathogen infection loads. Our results show that the social behavior of these salamanders leads to a higher probability of acquiring Bd, highlighting the complex effects that emergent pathogens may have on social species.

Many group-living individuals produce specific vocalizations while mobbing (when individuals move toward and harass a predator), a behavior that can recruit conspecifics. Although these vocalizations may be a source of information for heterospecifics, it remains largely unknown how heterospecifics respond to mobbing calls given by group-living species. In this study, we investigate whether the mobbing calls given by Western Australian magpies (Gymnorhina tibicen dorsalis) lead to the recruitment of heterospecifics. By presenting a taxidermied red fox (Vulpes vulpes)—representing a terrestrial predator threat—to a population of magpies and heterospecific species occupying the same area, we demonstrate that magpie calls given in response to a terrestrial predator recruit heterospecifics to the mobbing event. Heterospecifics are more likely to approach and engage in mobbing behavior when the predator is associated with magpie presence than when magpies are absent. We found that larger magpie groups produced more alarm calls than did smaller groups, but we found no evidence that group size affected heterospecific recruitment to the mobbing site. Therefore, the occurrence of magpie alarm calls, rather than the number of individuals giving alarm calls, seems to be the primary predictor of heterospecific recruitment to a mobbing site. Moreover, we used a playback experiment to test if heterospecifics responded more to single-magpie mobbing alarm calls than to single mobbing alarm calls given by a non-social species (red wattlebird, Anthochaera carunculata). We found that heterospecifics responded more to the playbacks of magpie than to red wattlebird alarm calls. Our study therefore suggests that Australian magpies may play a central role as information sources for heterospecific species during predator detection and mobbing events. Mobbing—when individuals move toward and vocalize or harass a predator—is a good example of interspecific communication. Loud vocalizations produced during mobbing behavior have been known to not only modify the behavior of the predator but to also recruit individuals to the mobbing event from a variety of different species. Although the response to heterospecific mobbing calls is becoming well documented, it remains largely unknown how heterospecifics respond to the mobbing calls of group-living species, even though these species can provide significant benefits for heterospecific species sharing the same habitat (via increased vigilance and predator detection rates for example). By presenting a predator model and using a series of playback experiments, we demonstrate that group-living Western Australian magpies may play a central role as information sources during predator detection and mobbing events.

The introduction of species outside their native range is an insidious form of human-induced environmental change, with mounting evidence that behaviour, either through plastic behavioural responses or adaptive changes, can play a vital role in mediating invasion success. In particular, when species invade non-native habitats, they often leave behind native predators. Altered predator assemblages may then result in changes to antipredator responses overtime. Here, we capitalise on the well-characterised invasion history of an Australian reptile, the delicate skink, Lampropholis delicata, to investigate differences in antipredator responses between an invasive island population (Lord Howe Island) and its original mainland source (Coffs Harbour) following 40 generations of isolation. Specifically, we examined the responses of invasive and native skinks to scent cues taken from huntsman spiders, Heteropoda sp., a predator present in both populations, and red-bellied black snakes, Pseudechis porphyriacus, a predator absent from the invasive range. We measured the time skinks took to emerge from a shelter site and subsequent basking and foraging behaviours in the absence and presence of each predator scent. We did not detect any differences in responses between native and invasive skinks, although predator scent affected foraging behaviour. In a separate experiment, lizards were faced with a simulated bird strike and had the choice of retreating under a snake-scented or unscented shelter. When faced with such a threat, we found that skinks did not avoid snake-scented shelters. We also measured the activity and exploratory behaviour of each skink prior to exposure to predator cues, finding that increased activity and exploration appears to be linked to reduced antipredator behaviour for invasive but not native skinks. Contrary to our initial predictions, our results suggest that the relaxation of pressure from native predators may not necessarily translate to changes in key antipredator responses in invasive species, even after 40 generations of isolation. Human movement introduce species into novel areas, where they are confronted with a suite of ecological challenges that must be navigated, including changes to predator assemblages, in order to successfully establish and become invasive. Altered predator assemblages encountered by invasive species may, in turn, result in changes to, or loss of, antipredator responses over time. We studied such a scenario in the delicate skink, an Australian lizard that has been repeatedly introduced to new areas. We compared the antipredator behaviour of skinks from an invasive island population to skinks from their original mainland source. We found that despite 40 generations of isolation, invasive skinks do not differ from native skinks in their antipredator behaviour. However, we found that greater activity and exploration levels had become linked to reduced antipredator behaviour in invasive but not native skinks.

Many biological invasions occur within and between urban areas. If native species adapted to anthropogenically altered habitats are subsequently moved from an urban area in their native range to one within a novel region, then their urban-specialized phenotypes may provide them an advantage via prior adaptation. Here we examine if urban-derived behavioral traits are present within native guttural toad, Sclerophrys gutturalis, populations (Durban, South Africa) and investigate whether these localized phenotypes persisted within their invasive populations in Mauritius and Reunion. In our study, we measured boldness and exploration in populations along the toad’s invasion route and found that toads were significantly bolder in urban populations, within both native and invasive ranges. This suggests boldness increased when toads transitioned to urban living in their native range and these heightened levels of boldness were maintained within invaded urban areas. This provides evidence that a bolder phenotype was a prior adaptation that likely increased guttural toad’s invasion success. Interestingly, toad boldness returned to pre-urbanization levels within invasive populations that spread into natural areas, replicated on both islands. Exploration, on the other hand, was not increased above pre-urbanization, or pre-invasion, levels for any of the populations, and was lower in toads from Mauritius. Overall, our findings suggest that increased boldness is favored in urban habitats and that urban-derived behavioral traits may provide individuals an advantage when invading new urban landscapes. Species adapting to anthropogenic landscapes have the ability to increase their invasive potential if the altered phenotypes they accrue can provide them advantages once they are transported outside their native range. Our study examined differences in behavioral traits, boldness, and exploration, along the invasion route of guttural toads, Sclerophrys gutturalis, between natural and urban sites from their native origin populations around Durban, South Africa, to their invasive populations in Mauritius and Reunion. We determined that populations were bolder in urban areas in their native range and that this increased boldness persisted in the other anthropogenic habitats within their invasive ranges, but reverted back to natural-native levels within populations that had spread into natural areas on both islands. Our findings support the growing trend that anthropogenically altered landscapes favor bolder individuals, as well as the assertion that urban-derived traits may bolster a species’ ability to establish and spread within novel landscapes.

Abstract In species that live in family groups, such as cooperative breeders, inbreeding is usually avoided through the recognition of familiar kin. For example, individuals may avoid mating with conspecifics encountered regularly in infancy, as these likely include parents, siblings, and closely related alloparents. Other mechanisms have also been reported, albeit rarely; for example, individuals may compare their own phenotype to that of others, with close matches representing likely relatives (“phenotype matching”). However, determinants of the primary inbreeding avoidance mechanisms used by a given species remain poorly understood. We use 24 years of life history and genetic data to investigate inbreeding avoidance in wild cooperatively breeding banded mongooses (Mungos mungo). We find that inbreeding avoidance occurs within social groups but is far from maximised (mean pedigree relatedness between 351 breeding pairs = 0.144). Unusually for a group-living vertebrate, we find no evidence that females avoid breeding with males with which they are familiar in early life. This is probably explained by communal breeding; females give birth in tight synchrony and pups are cared for communally, thus reducing the reliability of familiarity-based proxies of relatedness. We also found little evidence that inbreeding is avoided by preferentially breeding with males of specific age classes. Instead, females may exploit as-yet unknown proxies of relatedness, for example, through phenotype matching, or may employ postcopulatory inbreeding avoidance mechanisms. Investigation of species with unusual breeding systems helps to identify constraints against inbreeding avoidance and contributes to our understanding of the distribution of inbreeding across species. Significance statement Choosing the right mate is never easy, but it may be particularly difficult for banded mongooses. In most social animals, individuals avoid mating with those that were familiar to them as infants, as these are likely to be relatives. However, we show that this rule does not work in banded mongooses. Here, the offspring of several mothers are raised in large communal litters by their social group, and parents seem unable to identify or direct care towards their own pups. This may make it difficult to recognise relatives based on their level of familiarity and is likely to explain why banded mongooses frequently inbreed. Nevertheless, inbreeding is lower than expected if mates are chosen at random, suggesting that alternative pre- or post-copulatory inbreeding avoidance mechanisms are used.

Abstract Hummingbirds utilize visual cues to locate flowers, but little is known about the role olfaction plays in nectar foraging despite observations that hummingbirds avoid resources occupied by certain insects. We investigated the behavioral responses of both wild and captive hummingbirds to olfactory cues of hymenopteran floral visitors, including native wood ants (Formica francoeuri), invasive Argentine ants (Linepithema humile), and European honeybees (Apis mellifera). We demonstrate for the first time that hummingbirds use olfaction to make foraging decisions when presented with insect-derived chemical cues under field and aviary conditions. Both wild and captive hummingbirds avoided foraging on feeders with defensive chemicals of F. francoeuri and aggregation pheromones of L. humile, but showed no response to honeybee cuticular hydrocarbons. Our experiments demonstrate the importance of olfaction in shaping hummingbird foraging decisions. Significance statement Recent reviews reveal that avian olfaction is not just limited to vultures and a few taxa. We demonstrate that a very charismatic group, hummingbirds, avoid defensive and aggregatory chemical cues from insects present at nectar resources. Olfactory cues can provide critical information about the presence and potential threat of insect floral visitors. This study raises new questions about the underrated importance of olfaction in avian foraging and specifically, hummingbird foraging.

Biological invasions are a prominent example of human-induced environmental change that pose a significant threat to worldwide biodiversity. Recent evidence suggests that behavioural traits play a key role in mediating invasion success. However, little research has investigated how rapidly behavioural traits can change during the initial stages of invasion. We investigated the influence of invasion on behaviour in a recent aquatic invader, the Siamese fighting fish (Betta splendens), in northern Australia. These fish represent a recent introduction (ca. 2010) and are thought to be descended from ornamental varieties released into the wild from the aquarium trade. Using fish reared under captive conditions, we measured differences in three ecologically relevant behaviours (activity, foraging, and aggression) across invasive and domestic fighting fish. We found that fish descended from the recent invasive population were more active and consumed fewer food items than their domestic counterparts. Furthermore, foraging latency was repeatable in invasive, but not domestic fish, and this seemed to be driven by an increase in among-individual variation in the invasive population. Finally, while we detected a positive relationship between activity and number of food items eaten in domestic fish, this relationship was absent in the invasive population, suggesting that invasion may have disrupted this behavioural syndrome. Our results highlight that invasion can alter ecologically important behavioural traits and behavioural syndromes, even during the initial stages of invasion, and emphasise the importance of incorporating behaviour into our understanding of invasion biology. Alien species must rapidly adapt to novel environmental conditions in order to establish a successful invasive population. As behaviour mediates how organisms interact with their environment, behavioural traits may play a key role in facilitating invasion success. We investigated rapid changes in behavioural traits in a recently introduced (ca. 2010) ornamental fish, the Siamese fighting fish. We found that invasive fish differed from their domestic source population in two key behavioural traits—activity and foraging behaviour. Furthermore, we extend previous work by showing that invasion not only causes changes in average-level behavioural traits but can also result in changing patterns of behavioural variation and repeatability in newly established populations. Overall, our findings highlight that invasion can induce shifts in ecologically relevant behaviours, even during the early, crucial stages of invasion.

Generalist avian brood parasites commonly serve as a model system to test for plasticity in offspring growth and behavior under various host environmental and parental regimes. While past research has provided compelling evidence that developmental rates differ among hosts, the fitness consequences of such variation remain unclear. In hosts, carryover effects from the nesting to the post-fledging stage are critical in driving differential post-fledging survival within and among species, as well as the evolution of songbird life histories. Consequently, offspring of brood parasites may be subject to the same carryover effects and life history constraints observed in host species. Applying a pre- to post-fledging carryover effect framework to avian brood parasites may therefore provide novel insights into parasite life histories as well as parasite-host interactions. We assessed the potential influence of host carryover effects on the development and survival of juvenile cowbirds using empirical data from 10 realized host species in east-central Illinois, USA. We found that life history variation among juvenile cowbirds reflects variation in tradeoffs between mortality risk and nestling period length as well as pre- to post-fledging carryover effects found across host species. Cowbirds from host nests with higher mortality rates had shorter nestling periods, fledged with less developed wings, and exhibited higher rates of post-fledging mortality. Cowbird mass at fledging also predicted post-fledging survival, but was not associated with other life history traits. Our results provide novel links between juvenile growth, development, and mortality that help to explain differential survival in parasitic young across host species. Offspring of avian brood parasites develop at different rates based on the host environment in which they are raised, but the fitness consequences of such plasticity are poorly understood. Parasitic offspring may be subject to carryover effects from the nesting to the post-fledging stages and other life history constraints operating in host systems. We assessed the potential influence of host carryover effects on the development and survival of juvenile brown-headed cowbirds (Molothrus ater) using empirical data from 10 realized host species. Reflecting pre- to post-fledging carryover effects found across host species, cowbirds from host nests with higher mortality rates had shorter nestling periods, fledged with less developed wings, and exhibited higher rates of post-fledging mortality. Our results provide novel links between juvenile growth, development, and mortality that help to explain differential survival in parasitic young across host species.

Increased risk of pathogen transmission through proximity and contact is a well-documented cost of sociality. Affiliative social contact, however, is an integral part of primate group life and can benefit health. Despite its importance to the evolution and maintenance of sociality, the tradeoff between costs and benefits of social contact for group-living primate species remains poorly understood. To improve our understanding of this interplay, we used social network analysis to investigate whether contact via association in the same space and/or physical contact measured through grooming were associated with helminth parasite species richness in a community of wild chimpanzees (Pan troglodytes schweinfurthii). We identified parasite taxa in 381 fecal samples from 36 individuals from the Kasekela community of chimpanzees in Gombe National Park, Tanzania, from November 1, 2006 - October 31, 2012. Over the study period, eight environmentally transmitted helminth taxa were identified. We quantified three network metrics for association and grooming contact, including degree strength, betweenness, and closeness. Our findings suggest that more gregarious individuals - those who spent more time with more individuals in the same space - had higher parasite richness, while the connections in the grooming network were not related to parasite richness. The expected parasite richness in individuals increased by 1.13 taxa (CI: 1.04, 1.22; p = 0.02) per one standard deviation increase in degree strength of association contact. The results of this study add to the understanding of the role that different types of social contact plays in the parasite richness of group-living social primates.

Preferences for mating cues can have important effects on speciation in natural hybrid zones. While mating preferences of parental species are well studied, hybrid preferences for cues of parental species have received less attention. Nevertheless, hybrid preferences have potentially important consequences for reproductive isolation and patterns of introgression. Here, we test preferences in wild-caught hybrid chickadees for odor cues from the parental species, black-capped and Carolina chickadees. Olfaction has been historically understudied in avian species, especially passerines, but much recent work has begun to show how olfactory cues play important roles in songbird ecology. In contrast to the strong conspecific odor preferences we previously found in pure-species chickadees, male hybrids as a group show no preference for the odor of either parental species, while still exhibiting individual instances of preference. Female hybrids show preferences for black-capped odor, but this signature is driven by individuals with elevated proportions of black-capped ancestry while Carolina-like female hybrids show no preferences. We discuss the implications of a lack of some female hybrid preferences on reproductive isolation, and the potential for asymmetric preferences in male and black-capped-like female hybrids to contribute to directional introgression and northward movement of the hybrid zone. Mate preference has important implications for the fate of natural hybrid zones and the speciation process. Mating discrimination by pure species individuals against hybrids is commonly observed in hybrid zones. However, mate preferences of hybrid individuals for the parental species can be just as important. We previously found that hybrid zone black-capped and Carolina chickadees produce distinct odor profiles and show clear preferences for conspecific odor cues. Here, we assessed preferences of wild-caught hybrid chickadees for the odors of both parental species. In contrast to pure-species birds, hybrid males overall show no preference for either parental species odor as a group. Still, individual males do show clear preferences. Hybrid females show a preference for black-capped odor that is dependent on their own degree of black-capped ancestry. Carolina-like hybrid females show no preferences. Our results suggest the potential for hybrid preference to contribute to reproductive isolation and northward movement of the chickadee hybrid zone.

Abstract The source of maternal energy supporting reproduction (i.e., stored or incoming) is an important factor determining different breeding strategies (capital, income or mixed) in female mammals. Key periods of energy storage and allocation might induce behavioral and physiological shifts in females, and investigating their distribution throughout reproduction helps in determining vulnerable phases shaping female reproductive success. Here, we examined the effects of reproductive state on activity budget, feeding behavior, and urinary C-peptide (uCP) levels, a physiological marker of energy balance, in 43 wild female Assamese macaques (Macaca assamensis). Over a 13-month study period, we collected 96,266 instantaneous records of activity and 905 urine samples. We found that early lactating females and non-gestating–non-lactating females follow an energy-saving strategy consisting of resting more at the expense of feeding and consuming mostly fruits which contributed to enhancing their energy intake and feeding efficiency. We found an opposite pattern in gestating and late lactating females who feed more at the expense of resting and consume mostly seeds, providing a fiber-rich diet. Storing food into cheek pouches increased throughout gestation while it decreased all along with lactation. Lastly, we found the highest uCP levels during late gestation. Our results reflect different feeding adaptations in response to the energetic costs of reproduction and suggest a critical role of fat accumulation before conception and metabolizing fat during gestation and lactation. Overall, our study provides an integrative picture of the energetics of reproduction in a seasonal species and contributes to our understanding of the diversity of behavioral and physiological adaptations shaping female reproductive success. Significance statement To offset their substantial energetic investment in reproduction, mammalian females may modify their behavior and the way they extract energy from their environment. In addition, as a result of heightened energy expenditure, female reproduction might trigger physiological shifts. To date, most studies investigated the energetic costs of female reproduction using either a behavioral or a physiological approach. To arrive at a more comprehensive picture, we combined behavioral data with a physiological marker of energy balance, i.e., urinary C-peptide, in a seasonal primate species in its natural habitat. Our results indicate that throughout the reproductive cycle, behavioral and physiological adaptations operate concomitantly, inducing modifications in female activity budget, feeding behavior, and suggesting shifts in fat use. Overall, our results illustrate the relevance of combining data on behavior and hormones to investigate breeding strategies in coping with the energetic costs of reproduction.

There is growing evidence that animals gain information from heterospecifics, but utilising other species’ signals has rarely been reported in invertebrates. Herein, I conducted field experiments in a mixed colony of two crab species, Scopimera globosa and Austruca lactea, to test whether S. globosa discriminate several different displays of neighbouring male A. lactea. Three types of ‘intruders’ (male or female A. lactea, or a predatory crab, Helicana japonica) were exhibited to the ‘performer’ (male A. lactea) to elicit four different actions (courtship, aggressive, or defensive displays, or evasive behaviours). The actions of the performer, but not the presence of the intruder, were exhibited to the ‘audience’ (male A. lactea or S. globosa); the behaviours of the audience were recorded to analyse whether the audience could take advantage of the actions of neighbours. The evasive behaviour of performers elicited similar rates of evasive behaviours from conspecific and heterospecific audiences. Furthermore, courtship and aggressive displays of performers elicited significantly different rates of evasive behaviours from heterospecifics. The courtship displays of male A. lactea are more intensive than its aggressive displays; therefore, the reactions of S. globosa did not simply increase with the intensity of the performers’ displays. Presumably, S. globosa recognises that courtship displays by A. lactea do not indicate undesirable circumstances. Altogether, S. globosa were able to distinguish two types of displays as well as evasive behaviours of male A. lactea, an ability that may contribute to their estimation of the risk level of approaching intruders. By using field experiments, I demonstrated that sand-bubbler crabs distinguished the courtship and aggressive displays of fiddler crabs and showed evasive behaviours more frequently when they see the aggressive displays. The courtship displays of the fiddler crabs are more intensive than its aggressive displays; therefore, the reactions of the sand-bubbler crabs did not simply increase with the intensity of the performers’ displays. The displays of fiddler crabs were performed to other crabs (male or female fiddler crab, or a predatory crab) but not to the sand-bubbler crab; therefore, the sand bubbler crabs may have eavesdropped on heterospecific signals and utilised the heterospecific signals to predict the risk level of approaching intruders. To the best of my knowledge, distinguishing several signals of other species has been found only in some species of mammals, birds, or reptiles.

Many key questions in evolutionary ecology require the use of variance ratios such as heritability, repeatability, and individual resource specialization. These ratios allow researchers to understand how phenotypic variation is structured into genetic and non-genetic components, to identify how much organisms vary in the resources they use or how functional traits structure species communities. Understanding how evolutionary and ecological processes differ among populations and environments therefore often requires the comparison of these ratios across groups (i.e., populations, sexes, species). Inference based on comparisons of ratios can be limited, however. Variance ratios can remain the same across group despite very different values in the numerator and denominator variances. Moreover, evolutionary ecologists are most often interested in differences in specific variance components among groups rather than in differences in variance ratios per se. Recommendations for how to infer whether groups differ in variance are not clear in the literature. Using simulations, we show how questions regarding the estimation of variance components and their differences among groups can be answered with linear mixed models (LMMs). Frequentist and Bayesian frameworks have similar abilities to identify differences in variance components. However, variance differences at higher levels of organization can be difficult to detect with low sample sizes. We provide tools to conduct power analyses to determine the appropriate sample sizes necessary to detect differences in variance of a given magnitude. We conclude by supplying guidelines for how to report and draw inferences based on the comparisons of variance components and variance ratios Many critical questions in ecology and evolution use variance ratios, such as repeatability, heritability, or individual resource specialization, to make inferences about ecological and evolutionary processes. In many cases, these inferences rely on the comparison of variance ratios among datasets (populations, sexes, or environments). In this article, we show that current approaches of drawing inferences about group differences from comparisons of ratios are inappropriate because ratios can differ due to differences in the numerator, denominator, or both. We investigated how questions regarding differences in variance ratios and constituent variance components can be evaluated using linear mixed model (LMM) approaches and provide guidance for appropriate sampling schemes under different scenarios and discuss common pitfalls associated with estimation of differences in variance component among datasets.

Abstract Across the eusocial Hymenoptera, a queen’s mating frequency is positively associated with her workers’ genetic diversity and colony’s fitness. Over 90% of a colony’s diversity potential is achieved by its mother’s tenth effective mating (me); however, many females mate at levels of me > 10, a zone we here call hyperpolyandry. We compared honey bee colony fitness at mating levels near and above this genetic diversity asymptote. We were interested in how hyperpolyandry affects colony phenotypes arising from both common tasks (brood care) and rare specialized tasks (parasite resistance). We used an unselected wild line of bees and a Varroa Sensitive Hygiene (VSH) line selected to resist the parasite Varroa destructor. Virgin queens were instrumentally inseminated to replicate the following queen/colony conditions: (1) VSH semen/low polyandry (observed mating number = mo = 9), (2) VSH semen/high polyandry (mo = 54), (3) wild type semen/low polyandry, or (4) wild semen/high polyandry. There was a positive effect of polyandry on brood survival, an outcome of common tasks, with highest values at mo = 54. There was an interaction between polyandry and genetics such that differences between genetic lines expressed only at mo = 54, with fewer mites in VSH colonies. These results are consistent with two hypotheses for the evolution of mating levels in excess of the genetic diversity asymptote: hyperpolyandry improves colony fitness by (1) optimizing genotype compositions for common tasks and (2) by capturing rare specialist allele combinations, resisting cliff-edge ecological catastrophes. Significance statement Polyandry is a female’s practice of mating with several males, storing their sperm, and using it to produce one or more clutches of genetically diverse offspring. In the social Hymenoptera, polyandry increases the genetic diversity and task efficiency of workers, leading to improved colony fitness. Over 90% of the increase in a colony’s diversity potential is achieved by its mother’s tenth mating; however, many females practice hyperpolyandry, a term we reserve here for mating levels above this genetic diversity asymptote. We show that a token of colony fitness arising from common tasks, brood survival, improves universally as one moves from sub- to hyperpolyandrous mating levels. However, a colony phenotype arising from a rare parasite resistance task is only expressed in the presence of the controlling alleles and under conditions of hyperpolyandry. These results suggest adaptive mechanisms by which hyperpolyandry could evolve.

Social interactions are required for the direct transmission of infectious diseases. Consequently, the social network structure of populations plays a key role in shaping infectious disease dynamics. A huge research effort has examined how specific social network structures make populations more (or less) vulnerable to damaging epidemics. However, it can be just as important to understand how social networks can contribute to endemic disease dynamics, in which pathogens are maintained at stable levels for prolonged periods of time. Hosts that can maintain endemic disease may serve as keystone hosts for multi-host pathogens within an ecological community, and also have greater potential to act as key wildlife reservoirs of agricultural and zoonotic diseases. Here, we examine combinations of social and demographic processes that can foster endemic disease in hosts. We synthesise theoretical and empirical work to demonstrate the importance of both social structure and social dynamics in maintaining endemic disease. We also highlight the importance of distinguishing between the local and global persistence of infection and reveal how different social processes drive variation in the scale at which infectious diseases appear endemic. Our synthesis provides a framework by which to understand how sociality contributes to the long-term maintenance of infectious disease in wildlife hosts and provides a set of tools to unpick the social and demographic mechanisms involved in any given host–pathogen system. Supplementary Information The online version contains supplementary material available at 10.1007/s00265-021-03055-8.

Conspicuous signals, such as acoustic sexual signals, can be “risky” in that they may be overheard by competitors. This means the signaller must balance the benefits of signaling to the intended receiver with the costs of providing information to these competitors. Depending on the signaller context, this balance may change. Male humpback whales produce long, high amplitude songs. This conspicuous sexual signal is presumably used for advertisement when alone and possibly aimed at females when escorting. Regardless of which animal is the intended receiver, as it is conspicuous, it also available to multiple eavesdropping competitors. Here, we show a singing behavior in humpback whales that comprises of a series of “decisions” which depend on the singer’s context (advertising alone versus escorting a female) and the eavesdropping risk. In lone males not with a female, eavesdropping risk was not a significant factor in determining the “decision” to start singing and for how long. Escorting singers, however, were presumably at risk of losing a female to a competitor and were less likely to invest effort into singing as eavesdropping risk increased. Results suggest signaling males seem to be capable of assessing eavesdropping risk, and modifying their signaling behavior, according to the trade-off between the costs and benefits of signaling within each context. Given male humpback whales are using long-range communication signals available to a network of competitors, these trade-off “decisions” are likely to be complex. Humpback whale males use song as a long-range sexual signal. However, for any long-range conspicuous sexual signal, there is a direct trade-off between the advantages of using a conspicuous signal, with the cost of signaling to eavesdroppers such as rival males. Here, we showed that the “decisions” made by humpback whale singers depended on a combination of social factors including a social “trigger,” eavesdropping risk, and whether the singer was escorting a female. Results suggest male humpback whales are selecting the most appropriate singing strategy based on their assessment of a constantly changing, complex social environment.

Understanding the information content of animal displays is crucial for studying signal function and evolution. Previous works focused largely on display variations and their adaptation to background noise, with limited attention to the information content. Here, we explored the information content of tail displays of an Asian agamid lizard Phrynocephalus vlangalii and tested two non-exclusive hypotheses, the individual condition hypothesis and the resource quality hypothesis. We recorded individual tail display videos in the field under four social contexts and measured individual condition and burrow quality. Using linear regression and model selection, we tested associations between display variables and individual condition, as well as burrow quality variables. Fast tail coiling movement and large sweep area of tail lashing are respectively associated with fast sprint speed and large body size in males, while high tail coil amplitude is correlated with large body size in females. In addition, fast tail lashing movement is associated with shallow burrow in males, while in females, fast tail coiling movement is associated with small burrow entrance, and high amplitudes during tail coiling are associated with shallow burrow. Our results show that tail displays in these lizards indeed reflect individual body condition and burrow quality, and the information may help to alleviate social conflict and to assess potential mate quality. Furthermore, both females and males use tail displays to convey important information. Taken together, these results support both hypotheses and cast important insights on the content of tail displays in lizards, which will facilitate research on function and evolution of display signals. Many animals use visual displays to convey important information across a variety of contexts. We know much about display variations and their adaptations to background noises, but the information content of displays remains largely unclear, especially for species without colorful ornaments and sounds. This imposes significant limitations on understanding of display signal function and evolution. Here, we unraveled the content of tail displays in an Asian agamid lizard by testing two hypotheses using newly developed 3D methods. Consistent with condition and resource hypotheses, our results showed that variation of tail displays reflects individual body condition and burrow quality in the Asian agamid lizard, which suggests tail displays likely play important roles in alleviating social conflict and mate assessment in lizards. In addition, our study demonstrated a novel aspect that displays of females can also convey similar information as those of males.

The trade-off between lifespan and reproduction is central to our understanding of life-history evolution. Laboratory selection experiments have been a powerful tool for quantifying this trade-off, but these tend to be restricted in taxonomic scope, which may limit our understanding. In addition, research often focuses on the trade-off between lifespan and reproductive effort in females, and far less data test how lifespan trades off with different aspects of male reproduction (e.g. pre- and post-copulatory reproductive investment). Here, we examined the trade-off between lifespan and reproduction in females and males of the marula fruit fly, Ceratitis cosyra (Walker) (Diptera: Tephritidae). To do so, we selected downward or upward on age of peak female egg laying in C. cosyra for twenty generations. In multiple generations, we measured female and male lifespan and body size, female daily and lifetime fecundity, male courtship and mating success, as well as the number of sperm transferred at different ages and sperm storage asymmetry in spermathecae. Our selection regime appeared to achieve its aim; egg laying peaked earlier in females from downward selected lines than upward selected lines. The number of sperm transferred by males decreased in the upward selected flies, but other male reproductive traits remained the same across selection regimes. In contrast, with the wider literature, upward selection did not extend the lifespan of females or males after ten generations of selection. While lifespan in both sexes responded to selection on female egg laying schedules, it did not do so in a straightforward way. Moreover, male investment in reproductive traits was largely independent of selection regime. These counter-intuitive findings highlight the importance of working with a broad range of species and of considering the trade-off between reproduction and lifespan in both sexes. The trade-off between lifespan and reproduction has been extensively studied in model species using various types of laboratory selection. A limited number of species have been considered using this approach, and the majority of the studies have focused on female, rather than male, reproductive effort. Here, we selected downwards and upwards on age of female reproduction in the marula fruit fly and measured survival, female fecundity, reproductive schedule, as well as male sperm transfer, sperm storage asymmetry, mating and calling success. We found a moderate trade-off between lifespan and early fecundity in downward selected flies, whereas no obvious trade-off was observed in upward selected lines. Regardless of the selection regime, reproductive scheduling was affected in females but not in males, while lifespan was affected in both sexes. Our results show that the timing of reproduction can evolve independently across the sexes, highlighting the importance of studying both females and males.

Abstract The heterogeneity of resource availability shapes animal movements at different spatio-temporal scales. Given that movements at various scales are assumed to be linked, the space use of temperate ungulates within seasonal ranges (winter, summer) should be related to their movement patterns at the annual scale. In this study, we aimed to evaluate the level of stationarity of moose (Alces alces) within their seasonal ranges and to link annual movement patterns to within-season space use. We analysed the ranging behaviour of 32 moose fitted with GPS collars from two study areas in Eastern Poland, where at the annual scale a fraction of individuals migrate between summer and winter ranges (partial migration). Our results revealed that moose stationarity within seasonal home ranges expressed remarkable variation. The probability of moose stationarity within seasonal ranges was significantly higher (by 23%), and the mean home range size tended to be lower (9.7 km2) among individuals that seasonally migrated than among non-migratory moose (14.3 km2). In addition, we found that (i) in summer, moose were significantly more stationary (by 19%) and exhibited a smaller mean home range size than in winter (9.0 and 15.9 km2, respectively) and (ii) the mean seasonal home range size of males (19.6 km2) was remarkably greater than that of females (9.6 km2). Given the significant link between annual and seasonal scales of animal movements, any environmental change (e.g. climate warming) affecting an animal’s annual movement strategy could alter within-season animal space use and presumably individual fitness. Significance statement To maximize their fitness, animals adjust their movements to deal with variations in resource distribution in the landscape. The scale of spatio-temporal variation causes different types of migratory behaviours, ranging from year-round stationarity to migration, when individuals establish spatially separated seasonal ranges. Studies on ungulates suggest that the stability and the size of seasonal home ranges can be linked to annual movement behaviour. Using the locations of GPS-tracked moose, we demonstrate in this study that migratory individuals were more prone to establishing stable seasonal home ranges (especially in summer) than moose that occupied the same area throughout the year. Moreover, stable seasonal home ranges were remarkably smaller in summer than in winter, which may suggest a season-specific spatial distribution and a renewability of moose forage. Our results show a clear link between different temporal scales of animal movements.

Changes to the environment often affect animal behavior at the individual and group levels. For aquatic species, disturbances such as heavy rains and runoff may create a highly turbid (i.e., cloudy or visually obscured) environment, which potentially may affect individual interactions and group coordination. Surprisingly, we know little about how decreases in water clarity may influence important collective behavior, such as shoaling in fishes. We hypothesize that differences in water clarity would alter collective movement in fishes. We used an automated video tracking software to collect and process continuous, high-resolution spatial data in both clear and turbid waters. We studied two species of fishes that rely on vision for shoaling, the red shiner (Cyprinella lutrensis) and the sand shiner (Notropis stramineus). For each species, we used 20 groups of five fish each in a mixed-model design with three turbidity treatments: 0, 50–150, and 200–300 nephelometric turbidity units (NTUs). There were species-specific differences, but the patterns of response to turbidity were similar. Both species experienced decreased collective behavior in response to turbidity as indicated by significant increases in interfish distances and shoaling area as well as decreases in velocity. These findings show that turbidity may significantly influence collective behavior and group structure and are consistent with (but not conclusively so) a sensory limitation causation. We also provide basic knowledge in an area that is understudied and may be useful for conservation and management objectives, especially at a time when so many fishes are threatened due to habitat degradation and alteration. Collective behavior, i.e., coordinated behavior of groups of animals that often increases survivorship and fitness, occurs in many animals, e.g., schooling in fishes, flocking by birds, and herding by mammals. Habitats are being altered worldwide by human activities such as construction and agriculture. Using fishes, we studied how disruptions to the environment would alter collective behavior. Natural and human disturbances cause higher sedimentation and nutrient loads in aquatic habitats, causing water to become murky, i.e., turbid. We developed and used a computer program to study swimming patterns of shoaling fishes in such conditions. We found that fishes formed and maintained groups less efficiently as water became more turbid. Studies at various levels of the organization are essential in understanding the impacts of such disturbances to habitats, and this includes how disturbances to the environment can alter the collective behavior of fishes.

Abstract Males and females often have divergent evolutionary interests, generating sexual conflicts. This is particularly true in organisms that exhibit facultative sexuality, whereby females are capable of reproducing without fitness costs of mating. Here, we provide the first documented evidence with quantitative tracking showing that sex interacts with social context to determine space-use of females, in a pattern resembling predator avoidance. To achieve this, we labelled Daphnia magna with fluorescent nanoparticles and utilized a 3-D tracking platform to record pairs of individuals swimming. The recordings comprised either same-sex or opposite-sex pairings. We found that females swam faster, deeper, more horizontally, and more linearly when exposed to males than when exposed to females. Simultaneously, we found that male behavior did not differ depending on swimming partner and, importantly, we observed no sexual dimorphism in swimming behaviors when swimming with the same sex. Our results suggest that the presence of males in a population has the potential to influence the distribution of individuals, similarly to known threats, such as predation. This highlights that sexual conflict has clear spatial consequences and should be considered in such ecological frameworks, like the Landscape of Fear (LOF) concept. In a broader context, the connection of the evolutionary and social concept of sexual conflict and the ecological concept of LOF may improve our understanding of population dynamics and the spatial and temporal distribution of individuals in natural ecosystems. Significance statement Despite the wealth of studies that detail how predators affect their prey’s spatial behaviors, studies on the role of sex and social context on spatial behavior are rare. Addressing this dearth of information, we studied the swimming behaviors of an organism that can reproduce with or without sex, when exposed to an individual of either the same or opposite sex. We found no difference between the sexes in swimming behaviors; however, we revealed that females avoided males by swimming deeper in the water column, reminiscent of the response to predation. Our results highlight that social conflict between the sexes strongly affects the demographics of a population and may therefore have a substantial role in the spatial ecology of organisms in the wild.

In eusocial insects, worker polymorphism is shaped by several factors, including colony size, queen mating frequency, and the timing of queen-worker differentiation during larval development. In a comparative study of 18 species of Cataglyphis desert ants representing a wide range of worker sizes, we used phylogenetically controlled analyses to examine correlations between worker head width variation (i.e., worker polymorphism) and multiple social traits, namely, mature colony size, mean worker head width, queen head width, queen-worker head width dimorphism, and within-colony genetic relatedness, resulting from multiple mating by queens. We found that worker polymorphism was positively correlated with mature colony size, mean worker head width, and queen head width. In contrast, worker polymorphism was not correlated with queen-worker dimorphism and within-colony genetic relatedness. These results underscore that evolution of worker polymorphism and social traits are correlated. They also illustrate that additional research using multivariate approaches is needed to further clarify the evolution of insect societies. In eusocial insects, worker morphological variation (i.e., worker polymorphism) is tightly linked to division of labor. Multiple factors are supposed to shape the evolution of worker polymorphism. Using phylogenetically controlled analyses of worker head width variation from 18 species of Cataglyphis desert ants, we show that worker polymorphism positively correlates with mature colony size, mean worker head width, and queen size. These results highlight that the evolution of worker polymorphism and social traits are correlated. Identifying the mechanisms underlying these relationships could provide major insights into the development and evolution of insect societies.

Aggressive behaviours occur throughout the animal kingdom and agonistic contests often govern access to resources. Nutrition experienced during development has the potential to influence aggressive behaviours in adults through effects on growth, energy budgets and an individual’s internal state. In particular, resource-poor developmental nutrition might decrease adult aggression by limiting growth and energy budgets, or alternatively might increase adult aggression by enhancing motivation to compete for resources. However, the direction of this relationship—and effects of developmental nutrition experienced by rivals—remains unknown in most species, limiting understanding of how early-life environments contribute to variation in aggression. We investigated these alternative hypotheses by assessing male-male aggression in adult fruit flies, Drosophila melanogaster, that developed on a low-, medium- or high-resource diet, manipulated via yeast content. We found that a low-resource developmental diet reduced the probability of aggressive lunges in adults, as well as threat displays against rivals that developed on a low-resource diet. These effects appeared to be independent of diet-related differences in body mass. Males performed relatively more aggression on a central food patch when facing rivals of a low-resource diet, suggesting that developmental diet affects aggressive interactions through social effects in addition to individual effects. Our finding that resource-poor developmental diets reduce male-male aggression in D. melanogaster is consistent with the idea that resource budgets mediate aggression and in a mass-independent manner. Our study improves understanding of the links between nutrition and aggression.Significance statementEarly-life nutrition can influence social behaviours in adults. Aggression is a widespread social behaviour with important consequences for fitness. Using the fruit fly, Drosophila melanogaster, we show that a poor developmental diet reduces aspects of adult aggressive behaviour in males. Furthermore, males perform more aggression near food patches when facing rivals of poor nutrition. This suggests that early-life nutrition affects aggressive interactions through social effects in addition to individual effects.

Social networks capture the occurrence, direction and strength of pairwise interactions among individual animals in a group. Their structure has proven to be a key determinant of the patterns of parasite transmission and disease spread within groups. In contrast, little is known about how parasites themselves may have influenced the evolution of host social networks. Here, we use a comparative analysis among primate species to test the hypothesis that strong selective pressures exerted by parasites may have favoured the evolution of social network patterns that reduce the probability of infection. After controlling for variation in study effort and for host phylogeny, we find that social networks in primate species infected by multiple species of contagious (contact- or proximity-transmitted) parasites present slightly different topology than those in primates exposed to fewer parasites. In particular, we uncovered a positive relationship across primate species between parasite species richness and degree heterogeneity, that is, the coefficient of variation in number of social contacts per individual. While correlative evidence is insufficient to demonstrate causality, this result provides some support for our hypothesis on the link between host sociality and parasitism: host social networks shape patterns of intra-group parasite transmission, whereas selective pressures from parasites may in turn influence the structure of host social networks. Patterns of interactions among animals within a group form a social network, which provides a map of the possible routes of parasite transmission and disease spread within the group. At the same time, it is possible that selective pressures from the parasites themselves have shaped animal social networks, with species experiencing strong pressures from parasites (i.e. infected by many species of contagious parasites) having evolved social networks that limit the risk of infection for individual group members. We provide correlative evidence for the possible evolutionary influence of parasitism on social network structure, using a comparison among primate species. Our study provides a reversed narrative to the usual one in which social network structure drives infection.

Abstract Climate change and the subsequent increase of global temperature are the most current and important threats to biodiversity. Despite the importance of temperature, our knowledge about the level of behavioural and physiological adaptations of ant species from temperate regions to cope with high temperatures is limited compared to the broad knowledge of typical thermal specialists from warmer regions. In the current study, we investigated the temperature-related foraging risk of xerothermic ant species from the temperate climate in Europe, Formica cinerea. Our aims were to check how an increase in external soil temperature affects the foraging activity of workers and how the temperature during development and worker age affects foraging activity in high temperatures. Based on our results, we can draw the following conclusions: (1) the majority of workers utilize a risk-aversive strategy in relation to foraging in high surface temperatures; (2) pupal development temperature affects the risk taken by adult workers: workers that developed in a higher temperature forage more often but for shorter intervals compared to workers that developed in a lower temperature; (3) age is an important factor in temperature-related foraging activity, as with increasing age, workers forage significantly longer at the highest temperatures. Our study is one of the first to assess the potential factors that can affect the foraging risk of ants from a temperate climate in high ambient temperatures. Significance statement Our study is the first direct test of workers' age and the development temperature of pupae on the thermal-related foraging strategy of adult F. cinerea workers. It shows that worker age and the development temperature of pupae interact to promote tolerance of thermal stress. We found that with increasing age, workers are prone to forage significantly longer at the highest and riskiest temperatures. Workers that developed in the high temperature (28°C) foraged more often but for shorter intervals compared to workers that developed in the lower temperature (20°C). Interestingly, the factor of age is more significant for ants that developed in the higher temperature of 28°C; the foraging time of these ants significantly increased with their age.

The extent to which host group size affects the hosts’ exposure to parasites and pathogens has been explored by behavioral ecologists for almost 50 years, and we know that host and parasite taxa, mobility of host and parasite, and the extent of spatial structure within groups all affect the group-size relationship. Here we examine how the prevalence of an arthropod-borne viral pathogen changes with host group size in a host-parasite system recently invaded by an introduced species that also serves as a host for the virus. Infection by the alphavirus, Buggy Creek virus (BCRV), in swallow bugs (Cimex vicarius) increased with colony size of the cliff swallow (Petrochelidon pyrrhonota; the bugs’ principal host) in the absence of invasive house sparrows (Passer domesticus) but decreased with swallow colony size in the presence of sparrows. The sparrow-adapted lineage A of BCRV declined to near extinction in the largest cliff swallow colonies, regardless of sparrow presence. The results may reflect BCRV’s divergence into a lineage (B) that amplifies mostly in bugs and thus is transmitted more effectively in large cliff swallow colonies that maintain high numbers of the blood-feeding bugs, whereas the other lineage (A) is adapted to house sparrows and does not require large numbers of bugs and cliff swallows for effective transmission and persistence. The results show that an alternative host can modify the group-size consequences for the original host and illustrate another complexity in analyzing the costs and benefits of coloniality whenever invasive species are present. Predicting the spread of viral pathogens can be important in assessing threats to wildlife or humans, and the size of a host’s social group is regarded as a potentially important determinant of pathogen exposure. Invasive species can sometimes profoundly alter disease dynamics when they enter a host-parasite system and serve as alternative hosts, thereby either increasing or decreasing the original host’s exposure to pathogens. For an arthropod-borne virus that is vectored by a blood-feeding bug that parasitizes a colonially breeding bird, we found that virus infection in bugs increased with host (bird) group size when an invasive bird species was absent but decreased with host group size when the invasive was present. The study indicates that the presence of alternative hosts is another variable to consider in trying to predict how pathogen exposure is affected by host group size.

Many species rear offspring in fixed sites, returning frequently to provision them, and the selection of these sites is a critical decision in the life cycle, as they may in some instances increase susceptibility to predators. African wild dogs are a groupliving large carnivore that rear their offspring in fixed sites, provisioning dependent pups in dens for 3 months post-birth. Where possible, African wild dogs select den sites in rocky terrain, and it is hypothesised that this is because lions, their main predators, generally avoid this habitat. In the Okavango Delta, Botswana, there is a lack of rocky terrain, providing an opportunity to assess whether lions drive den site selection. GPS collar data from 7 impala and 4 lions revealed that both species prefer to reside in grassland and mixed woodland habitats, demonstrating that these are high risk/reward areas for African wild dogs. Using GPS collar data from 16 African wild dog packs over 8 years, our study characterised 116 African wild dog den sites identified in the field. Packs showed a preference for denning in mopane woodland, which lions avoid, and packs commuted further from the den each day as the den’s distance to grassland and mixed woodland increased, suggesting a preference for hunting in this habitat. Our results suggest that African wild dogs trade-off the costs of commuting and predation risk, such that longer commuting costs confer increased safety. Species which utilise dens, nests, or other fixed sites to rear offspring must balance the need to protect their young from predators with the need to acquire resources for themselves and their young. The selection of den sites is expected to be of considerable importance to enable the animal to meet these two requirements and successfully raise young. Our study of African wild dogs indicates that they select dens in resource-scarce areas which are likely to minimise interactions with their main predator, lions. This increases the distance to prey-rich areas and therefore the cost of hunting. Availability of appropriate habitat for both hunting and denning is therefore important when considering landscapes appropriate for African wild dog conservation, energetic constraints of breeding, and home-range indices.

In socially monogamous animals, maintaining stable mating pairs across years has been hypothesized to result in increased reproductive success. However, previous individual breeding experience may independently affect reproductive success, regardless of pair stability. We examined associations between pair composition based on previous breeding experience, pair longevity, and reproduction in socially monogamous mountain chickadees, Poecile gambeli, in the Sierra Nevada. There were no significant differences in any reproductive parameters between pairs of experienced breeders that had bred together in previous years and those that were newly formed. Pairs in which both partners were experienced had heavier nestlings than both first-year breeders and mixed experienced–inexperienced pairs. Experienced females started laying eggs earlier and laid larger clutches regardless of their social mate’s previous breeding experience. As all experienced birds were older than inexperienced breeders, it remains possible that observed differences between these groups were due to age rather than breeding experience. Overall, our data did not support the hypothesis that pair longevity drives reproductive investment. We showed that pair longevity in birds with previous experience had no significant association with any reproductive parameters. Instead, we detected that individual-level characteristics related to either previous breeding experience or age (first-year breeders vs. older, experienced breeders) were associated with earlier breeding, larger clutch size, and heavier nestlings. While it remains unclear whether age, breeding experience, or both influence the observed differences in reproductive investment, our results do suggest that pair longevity may not be a critical determinant of reproductive investment in a relatively short-lived, socially monogamous species.

Quantifying the costs of mating is key for understanding life-history trade-offs. As a reflection of metabolic rate, body temperature is one metric for assaying these costs. However, conventional methods for measuring body temperature are invasive and unsuitable for the study of free-living populations of endangered species, including great apes. A promising proxy for body temperature is fecal temperature, the internal temperature of fecal deposits shortly following defecation. We validated this method with humans, finding that maximum fecal temperature is a reliable proxy for rectal temperature. We then applied this method to wild chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda. We collected and analyzed 101 fecal temperature measurements from 43 adult chimpanzees (male: N = 28; female: N = 15). Chimpanzee fecal temperature ranged from 33.4 to 38.9 °C, with a mean of 35.8 °C. Although fecal temperature was not predicted by sex, age, or ambient temperature, male fecal temperature was 1.1 °C higher on days when sexually receptive females were present and was positively correlated with male dominance rank. Post hoc analyses showed that overall copulation rates, but not aggression rates, were positively correlated with fecal temperature, suggesting that sexual physiology and behavior best explain mating-related temperature variation. Together, these results indicate fecal temperature is a reliable proxy for core body temperature in large-bodied mammals, captures metabolic costs associated with male mating behavior, and represents a valuable noninvasive tool for biological field research. Body temperature illuminates an animal’s physiological condition and energy expenditure, but it is difficult to measure in wild animals. Consequently, basic data on body temperature and its socioecological correlates in wild animals are scant, especially when noninvasive measures must be used. To address this problem, we demonstrated that the temperatures of fecal deposits reliably estimate body temperatures in a large bodied primate and are approximately as reliable as invasive, subcutaneous transponder methods used in other mammals. We then found that fecal temperature in chimpanzees varied by ecologically and reproductively relevant variables including time of year, the presence of sexually receptive females, and dominance rank. Sexual behavior was likely responsible for increased male fecal temperature, as overall copulation frequency, but not aggression, was correlated with fecal temperature. We therefore provide evidence that fecal temperature can be used to assay body temperature and address questions regarding physiological condition and metabolic expenditure.

In cooperatively breeding species, the level of investment by both breeders and helpers may be influenced by the sex of offspring in broods that they attend, due to different fitness payoffs associated with investing in male versus female offspring. This might be expected if the sexes differ markedly in either the cost of their rearing, due to factors such as sexual size dimorphism, or the level of help that they may provide in later life that might benefit helpers in the future. Here we investigate how nestling sex influences the provisioning efforts provided by helpers and the subsequent growth and development of offspring in the cooperatively breeding noisy miner (Manorina melanocephala). In this species, helpers are predominantly philopatric males, as females disperse to other colonies to find breeding positions. We therefore predicted that helpers might invest more in helpful male-biased broods rather than those with dispersive female offspring, particularly if larger males required more resources than female offspring to successfully fledge. Male miners grew faster, fledging at the same age as their female siblings but with a heavier body mass. Male offspring therefore possibly require more resources than female offspring to raise. However, despite possible differences in the fitness returns of investing in different sexes, we were unable to detect any significant influence of brood sex ratio on the provisioning rate of pair or their helper contingent. Noisy miner helpers provision the brood irrespective of offspring sex. This could be due to an inability to recognise nestling sex, or potential future costs that might be imposed by philopatric males that subsequently compete for resources and/or mating opportunities with the helpers that reared them. From a male helper perspective, these potential costs may ultimately nullify benefits that male offspring provide in future. Male and female offspring might have different fitness benefits for helpers in the cooperatively breeding species. Given this, helpers in this breeding system might have sex-dependant preferences and direct their help towards the apparently more beneficial sex (i.e. the sex that is expected to stay at the same population and provide help in return). In this study, we showed that in the cooperatively breeding noisy miner (Manorina melanocephala), although male offspring are expected to provide higher level of care with over 90% of helpers being male, this apparent difference in the fitness return did not result in higher provisioning rate in the male-biased broods compared to female-biased broods. We argue that (a) this could be due insufficient cues for recognition of nestling sex or (b) despite the higher level of help that male offspring are expected to provide into the future, the overall inclusive fitness benefits do not vary among the sexes.