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Background The reproductive division of labor of eusocial insects, whereby one or several queens monopolize reproduction, evolved in a context of high genetic relatedness. However, many extant eusocial species have developed strategies that decrease genetic relatedness in their colonies, suggesting some benefits of the increased diversity. Multiple studies support this hypothesis by showing positive correlations between genetic diversity and colony fitness, as well as finding effects of experimental manipulations of diversity on colony performance. However, alternative explanations could account for most of these reports, and the benefits of diversity on performance in eusocial insects still await validation. In this study, we experimentally increased worker diversity in small colonies of the ant Lasius niger while controlling for typical confounding factors. Results We found that experimental colonies composed of workers coming from three different source colonies produced more larvae and showed more variation in size compared to groups of workers coming from a single colony. Conclusions We propose that the benefits of increased diversity stemmed from an improved division of labor. Our study confirms that worker diversity enhances colony performance, thus providing a possible explanation for the evolution of multiply mated queens and multiple-queen colonies in many species of eusocial insects. Supplementary Information The online version contains supplementary material available at 10.1186/s12862-021-01890-x.

The evolution of cooperation requires more benefits of group living than solitary lifestyle. However, to some degree, our understanding about the benefits is hindered by abstract debates over theoretical and experimental evidences of individual selection or group selection because it is difficult to examine the actual benefits at the group level. Moreover, group density is a crucial ecological factor which deeply affects group reproduction and survival, few studies have been performed in social insects. Here, we study the effects of worker density on group direct benefits in the termite species Reticulitermes chinensis. The termite R. chinensis is an ideal model which lives with a high worker density in wood. We used the quantity of eggs and the total biomass (biomass of all group members) accumulation as two components of group benefits. We investigated the group benefits in the context of worker density according to eleven worker densities, and we measured the group benefits and the resource consumption with the same group members in two types of artificial nest areas. Moreover, we counted the stomodeal trophallaxis occurrences from any workers to queens under three worker densities to explore the degree of cooperation according to worker density. We found that both the number of eggs and the total biomass accumulation significantly increased with increasing worker density in groups. Furthermore, the consumption of resources was similar between groups with the same number of individuals gathered in small or large nest areas, but the production of eggs and the biomass accumulation were higher in groups of small nest areas than in large nest areas. Additionally, we found the stomodeal trophallaxis behavior significantly increased in higher worker density groups. Our results suggest that the group benefits influenced by the high worker density may at least partially explain the group living of eusocial insects in ecology.

The social mole-rats of the family Bathyergidae show elaborate social organisation that may include division of labour between breeders and non-breeders as well as across non-breeders within their groups. However, comparative behavioural data across the taxa are rare and contrasts and similarities between species are poorly understood. Field studies of social bathyergids usually involve capturing all group members until the entire group is captured. Because each animal is only captured once and traps are typically placed in close proximity to active foraging areas, the order in which animals are captured provides an indication of the foraging activity of different individuals and of the spatial organisation of the group within the burrow system. Here, we compare the association of capture order with breeding status, sex, and body mass in four species and subspecies of social bathyergids, which vary in group size and represent all three social genera within the family Bathyergidae. We show that in naked and Damaraland mole-rats (Heterocephalus glaber and Fukomys damarensis), male and female breeders are captured later than non-breeders, whereas in two different subspecies of the genus Cryptomys only female breeders are captured later than non-breeders. The effect sizes vary largely and are 10 times larger in naked mole-rats as compared to Fukomys and 3–4 times larger than in Cryptomys. Among non-breeders, sex effects are notably absent in all species and body mass predicted capture order in both naked and Damaraland mole-rats. In naked mole-rats, larger non-breeders were captured earlier than smaller ones, whereas in Damaraland mole-rats intermediate-sized non-breeders were captured first. Our data suggest that there are similarities in behavioural structure and spatial organisation across all social bathyergid species, though the most pronounced differences within groups are found in naked mole-rats.

Social insects are well known for their aggressive (stinging) responses to a nest disturbance. Still, colonies are attacked due to the high-protein brood cached in their nests. Social wasps have evolved a variety of defense mechanisms to exclude predators, including nest construction and coordinated stinging response. Which predatory pressures have shaped the defensive strategies displayed by social wasps to protect their colonies? We reviewed the literature and explored social media to compare direct and indirect (claims and inferences) evidence of predators attacking individuals and colonies of wasps. Individual foraging wasps are predominantly preyed upon by birds and other arthropods, whereas predators on wasp brood vary across subfamilies of Vespidae. Polistinae wasps are predominantly preyed upon by ants and Passeriformes birds, whereas Vespinae are predominantly preyed upon by badgers, bears, and hawks. Ants and hornets are the primary predators of Stenogastrinae colonies. The probability of predation by these five main Orders of predators varies across continents. However, biogeographical variation in prey–predator trends was best predicted by climate (temperate vs. tropical). In social wasps’ evolutionary history, when colonies were small, predation pressure likely came from small mammals, lizards, or birds. As colonies evolved larger size and larger rewards for predators, the increased predation pressure likely selected for more effective defensive responses. Today, primary predators of large wasp colonies seem to be highly adapted to resist or avoid aggressive nest defense, such as large birds and mammals (which were not yet present when eusociality evolved in wasps), and ants.

BackgroundThe developmental fates of offspring have the potential to be influenced by the identity of their care-givers and by the nature of the care that they receive. In animals that exhibit both parental and alloparental care, such as the annually eusocial insects, the influence of care-giver identity can be directly assessed to yield mechanistic and evolutionary insights into the origins and elaboration of brood care. Here, we performed a comparative investigation of maternal and worker brood care in bumble bees, a pollinator group where mothers (queens) rear the first offspring in the nest, and then daughters (workers) assume this role upon their emergence. Specifically, we compared the effects of queen and worker brood care on offspring development and also offspring performance, for a set of traits related to sensory biology, learning, and stress resistance.ResultsWe found that queen-reared workers were smaller-bodied than worker-reared offspring, suggesting that bumble bee queens influence body size determination in their offspring. We also found that queen-reared workers were more resistant to starvation, which might be beneficial for early nesting success. These maternal influences could not be explained by feeding rate, given that we detected a similar offspring feeding frequency in both queens and workers.ConclusionBumble bee queens have a unique influence on the development of the first offspring in the nest, which they rear, relative to worker-reared workers. We propose that bumble bee brood care has been shaped by a suite of evolutionary and ecological factors, which might include a maternal influence on traits that promote survival of incipient colonies.

Many eusocial insects, including ants, show complex colony structures, distributions, and reproductive strategies. In the ant Vollenhovia emeryi Wheeler (Hymenoptera: Myrmicinae), queens and males are produced clonally, while sterile workers arise sexually, unlike other ant species and Hymenopteran insects in general. Furthermore, there is a wing length polymorphism in the queen caste. Despite its evolutionary remarkable traits, little is known about the population structure of this ant species, which may provide insight into its unique reproductive mode and polymorphic traits. We performed in‐depth analyses of ant populations from Korea, Japan, and North America using three mitochondrial genes (COI, COII, and Cytb). The long‐winged (L) morph is predominant in Korean populations, and the short‐winged (S) morph is very rare. Interestingly, all L morphs were infected with Wolbachia, while all Korean S morphs lacked Wolbachia, demonstrating a association between a symbiont and a phenotypic trait. A phylogenetic analysis revealed that the S morph is derived from the L morph. We propose that the S morph is associated with potential resistance to Wolbachia infection and that Wolbachia infection does not influence clonal reproduction (as is the case in other ant species).

Semi‐natural habitats are characterized by a high diversity of wildlife. However, other areas, e.g. old fields, can also play an important role in biodiversity conservation. We assessed the species richness, abundance, and diversity of wild bees (Apiformes), including species of various functional groups in two contrasting and differently managed landscape types. For this study, we selected 15 xerothermic or sandy grasslands or extensively managed fresh meadows located in agricultural landscapes as well as 15 old fields located in wooded landscapes. The study sites differed in area, stage of succession, and management regime. We did not detect any significant differences in total species richness, abundance, and diversity of Apiformes between the two landscape types, which suggests that both semi‐natural habitats and old fields are highly attractive to bees. The two habitat types, however, differed in species composition and proportions of functional groups. We found that in wooded landscapes, eusocial, hive‐nesting, and large‐sized species increased in abundance. The collected information on the preferences of Apiformes in respect of various habitats and landscapes makes it possible to protect and restore valuable habitats through the implementation of suitable methods of management, both locally and on the scale of landscapes.

Inbreeding can have negative consequences on population viability because of the reduced fitness of the progeny. In general, most species have developed mechanisms to minimize inbreeding such as dispersal and kin avoidance behavior. In the eusocial Hymenoptera, related individuals typically share a common nest and have relatively short mating periods, this could lead to inbreeding, and because of their single?locus complementary sex determination system, it may generate diploid males that could result in infertile triploid progeny representing a cost for the colony. Vespula germanica, is an eusocial wasp that has invaded many parts of the world, despite likely facing a reduced genetic pool during the arrival phases. We ask whether male wasp display specific aggregation behavior that favors genetic diversity, key to reduce inbreeding. Through a set of laboratory experiments, we investigated the effects of drone nestmateship and density on the aggregation behavior of V. germanica drones. We show that drones avoid aggregating with their nestmates at all densities while non-nestmates are avoided only at high densities. This suggests that lek genetic diversity and density could be regulated through drone behavior and in the long run minimize inbreeding favoring invasion success. Fil: Masciocchi, Maité. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche. Instituto de Investigaciones Forestales y Agropecuarias Bariloche. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; Argentina Fil: Angeletti, Bárbara. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche. Instituto de Investigaciones Forestales y Agropecuarias Bariloche. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; Argentina Fil: Corley, Juan Carlos. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche. Instituto de Investigaciones Forestales y Agropecuarias Bariloche. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; Argentina Fil: Martinez Von Ellrichshausen, Andres Santiago. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche. Instituto de Investigaciones Forestales y Agropecuarias Bariloche. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; Argentina

Evolutionary forces of selfishness, reciprocity, and kin selection can bring groups of animals together. This chapter includes cooperation in birds and invertebrates starting with aggregated nesting in swallows. In swallows, a distinct monogamous pair maintains each nest and the aggregation results from widespread attraction of birds to (limited) good nesting sites, as well as possible benefits from shared vigilance against predators. Sociable weavers and acorn woodpeckers both nest cooperatively, with shared nest construction and maintenance and, particularly in acorn woodpeckers, cooperative rearing of nestlings. In invertebrates, there are numerous examples of eusociality. They include gall-occupying plant feeders, shrimp, termites, ants, wasps, and bees. Invertebrate eusocial societies typically feature division of labor in colonies that makes the social group ecologically efficient. Division of labor contributes much to the dominant ecological roles of these animals. Reproductive differences between queens and workers are maintained, highlighting evolutionary implications of worker reproductive suppression. Eusocial invertebrates hold substantial resources in their nest and become targets for predation. This has stimulated novel and highly effective defensive strategies. Stinging, biting, and chemical defenses are all present in eusocial invertebrates. The breadth of ecological roles and behavioral adaptations in eusocial animals correlates with their ecological dominance.

The origin of eusociality in the Hymenoptera is a question of major interest. Theory has tended to focus on genetic relatedness, but ecology can be just as important a determinant of whether eusociality evolves. Using the model of Fu et al. (2015), we show how ecological assumptions critically affect the conclusions drawn. Fu et al. inferred that eusociality rarely evolves because it faces a fundamental ‘risk‐return tradeoff’. The intuitive logic was that worker production represents an opportunity cost because it delays realising a reproductive payoff. However, making empirically justified assumptions that (1) workers take over egg‐laying following queen death and (2) productivity increases gradually with each additional worker, we find that the risk‐return tradeoff disappears. We then survey Hymenoptera with more specialised morphological castes, and show how the interaction between two common features of eusociality – saturating birth rates and group size‐dependent helping decisions – can determine whether eusociality outperforms other strategies., Theories concerning the origin of eusociality in Hymenoptera have tended to focus on genetic relatedness, but ecology can be just as important. With realistic ecological assumptions, we show that eusociality does not face a previously postulated ‘risk‐return tradeoff’. We find that the interaction between two common features of eusociality – birth rates that saturate at large group sizes, and group‐size dependent helping decisions – can instead determine whether eusociality outperforms other strategies.

Eusociality represents an extreme form of social behavior characterized by a reproductive division of labor. Eusociality necessarily evolved through kin selection, which requires interactions among related individuals. However, many eusocial taxa also show cooperation between non-kin groups, challenging the idea that cooperative actions should only occur among relatives. This review explores the causes and consequences of non-kin cooperation in ants. Ants display a diversity of behaviors that lead to non-kin cooperation within and between species. These interactions occur among both reproductive and non-reproductive individuals. The proximate and ultimate mechanisms leading to non-kin cooperative interactions differ substantially depending on the biotic and abiotic environment. We end this review with directions for future research and suggest that the investigation of non-kin cooperative actions provides insight into processes leading to social evolution.

Background The ‘genetic diversity’ hypothesis posits that polyandry evolved as a mechanism to increase genetic diversity within broods. One extension of this hypothesis is the ‘genetic diversity for disease resistance’ hypothesis (GDDRH). Originally designed for eusocial Hymenoptera, GDDRH states that polyandry will evolve as an effect of lower parasite prevalence in genetically variable broods. However, this hypothesis has been broadly applied to several other taxa. It is unclear how much empirical evidence supports GDDRH specifically, especially outside eusocial Hymenoptera. Results This question was addressed by conducting a literature review and posteriorly conducting meta-analyses on the data available using Hedges’s g. The literature review found 10 direct and 32 indirect studies with both having a strong publication bias towards Hymenoptera. Two meta-analyses were conducted and both found increased polyandry (direct tests; n = 8, g = 0.2283, p = n = 10, g = 0.21, p = Conclusion Despite the fact that the GDDRH was developed for Hymenoptera, it is frequently applied to other taxa. This study highlights the low amount of direct evidence supporting GDDRH, particularly outside of eusocial Hymenoptera. It calls for future research to address species that have high dispersal rates and contain mixes of solitary and communal nesting.

Funder: Calico Life Sciences, LLC, The naked mole‐rat (Heterocephalus glaber) has fascinated zoologists for at least half a century. It has also generated considerable biomedical interest not only because of its extraordinary longevity, but also because of unusual protective features (e.g. its tolerance of variable oxygen availability), which may be pertinent to several human disease states, including ischemia/reperfusion injury and neurodegeneration. A recent article entitled ‘Surprisingly long survival of premature conclusions about naked mole‐rat biology’ described 28 ‘myths’ which, those authors claimed, are a ‘perpetuation of beautiful, but falsified, hypotheses’ and impede our understanding of this enigmatic mammal. Here, we re‐examine each of these ‘myths’ based on evidence published in the scientific literature. Following Braude et al., we argue that these ‘myths’ fall into four main categories: (i) ‘myths’ that would be better described as oversimplifications, some of which persist solely in the popular press; (ii) ‘myths’ that are based on incomplete understanding, where more evidence is clearly needed; (iii) ‘myths’ where the accumulation of evidence over the years has led to a revision in interpretation, but where there is no significant disagreement among scientists currently working in the field; ( iv ) ‘myths’ where there is a genuine difference in opinion among active researchers, based on alternative interpretations of the available evidence. The term ‘myth’ is particularly inappropriate when applied to competing, evidence‐based hypotheses, which form part of the normal evolution of scientific knowledge. Here, we provide a comprehensive critical review of naked mole‐rat biology and attempt to clarify some of these misconceptions.

For eusocial insects, the nest is a place where the main social interactions occur. The nest architecture ensures protection from predators and the environment, as well as suitable conditions for brood rearing, food storage, and in some cases the cultivation of fungus farms. Variations in nest architecture can occur, according to the environmental conditions. In order to elucidate the internal organization of nests, most studies use 2D schemes and photographs to illustrate the nest architecture models. However, 3D models can provide a different and more realistic view of the nest architecture. The aim of this study was to describe the nest architecture and colony size of the grass-cutting ant Acromyrmex balzani (Emery), using 3D models to illustrate these features. The structures of eight colonies were measured and the data were used to create a 3D model of each nest. Externally, the nests had one or more piles of loose soil and waste, with a single straw turret over the entrance. Underground, the nests had from 2 to 6 chambers, at a maximum depth of 122 cm. It could be concluded that the observed nest architecture of Acromyrmex balzani followed, at least in part, the pattern already reported in the literature. However, this is the first report of connection between two chambers made by two shafts, as well as the presence of the turret at the nest entrance/exit, regardless of the season of the year. These differences evidence that the nest structures may vary, depending on intrinsic or local environmental conditions.

Bees play a key role in ecosystem services as the main pollinators of numerous flowering plants. Studying factors influencing their foraging behavior is relevant not only to understand their biology, but also how populations might respond to changes in their habitat and to the climate. Here, we used radio-frequency identification tags to monitor the foraging behavior of the neotropical stingless beeMelipona fasciculatawith special interest in drifting patterns i.e., when a forager drifts into a foreign nest. In addition, we collected meteorological data to study how abiotic factors affect bees’ activity and behavior. Our results show that only 35% of bees never drifted to another hive nearby, and that factors such as temperature, humidity and solar irradiation affected the bees drifting rates and/or foraging activity. Moreover, we tested whether drifting levels would decrease after marking the nest entrances with different patterns. However, contrary to our predictions, there was an increase in the proportion of drifting, which could indicate factors other than orientation mistakes playing a role in this behavior. Overall, our results demonstrate how managed bee populations are affected by both nearby hives and climate factors, offering insights on their biology and potential commercial application as crop pollinators.

Among eusocial Hymenoptera, ants represent an unrivalled example of diversity in number of queens and mating systems. Ant colonies may have one (monogyny) or several queens (polygyny) which can mat...

Nearly half of all terrestrial tropical ecosystems around the globe comprise dry forests, characterised through elevated temperatures all year round, and short rainy seasons at irregular intervals. The consequent water deficit over several consecutive months limits the availability of floral resources to often very brief and unpredictable periods, which poses a challenge to the maintenance of perennial colonies in highly eusocial bees. Thus, only few highly eusocial bees occur permanently in tropical dry forests, among them some highly adapted species of stingless bees (Apidae, Meliponini). In the present review, we discuss the current knowledge on the adaptations to such extreme environments in Melipona subnitida, a stingless bee native to the Brazilian tropical dry forest. Key to the success of this species is not so much heat resistance of foragers, as it is the ability to maintain perennial colonies despite extended dearth periods. After several months of drought, M. subnitida colonies are capable of re-establishing fully functional colonies from nests containing only few dozens of workers. This surprising resilience is based on a quick reaction to precipitation-driven increase in floral resource availability, mainly owing to selective foraging at high-profit resources and an immediate up-regulation of brood production once food storage conditions improve.

Ants are a hugely diverse family of eusocial insects that dominate terrestrial ecosystems all over the planet. Did mutualistic gut microbes help ants to achieve their diversity and ecological dominance? Initial studies suggested the potential for widespread convergence in ant gut bacterial communities based on dietary niche, but it now seems possible that dedicated bacterial symbionts are restricted to a minority of ant lineages (Russell et al., ). Nevertheless, as most ants are omnivores, the evidence so far has suggested a broad, positive correlation between the evolution of dietary specialization and ant investment in nutrient-provisioning gut bacteria. In this issue of Molecular Ecology, Sapountzis et al. () and Rubin et al. () examine the evolution of gut bacterial communities in two iconic ant taxa-the attine fungus farmers and the Pseudomyrmex plant bodyguards, respectively-in a comparative context. By comparing gut bacteria between ant species of differing dietary specialization within each taxon, these studies demonstrate a hint of convergence in the midst of widespread apparent constraints. These results raise numerous interesting questions about the nature of these apparent constraints and whether they are causes or consequences of varying investment by ants to mutualism with their gut microbes.

African mole-rats are subterranean rodents, which rarely if ever leave the safety of their burrow systems. The environment of the burrows is humid, with relatively stable temperatures, and may have a hypoxic and hypercapnic atmosphere. One of crucial problems related to the subterranean way of life in mammals is avoidance of overheating, because traditional mammalian cooling mechanisms are not effective under high humidity. In African mole-rats, a variety of adaptations have evolved in response to this and other challenges of the underground ecotope. Traditionally, attention has been devoted mainly to the naked mole-rat Heterocephalus glaber, which became popular as a result of its eusociality and absence of fur, both being unique phenomena in small mammals. Despite more recent research, information on other species is still relatively limited and patchy. I review the results of studies on African mole-rats that are relevant for the understanding of their energetics and thermal biology. Attention is paid to the parameters of the burrow environment, which represent the main selection pressures shaping their physiology. In addition, an overview is given of the morphological, physiological and behavioural adaptations helping mole-rats to face temperature extremes, mechanisms by which they deal with a surplus of metabolic heat and how changes in ambient temperature influence their daily activity. The naked mole-rat is compared to its furred relatives to determine whether this species is really exceptional from the point of thermal biology. An ordination analysis was conducted using published data on mole-rat body temperature, thermoneutral zone, resting metabolic rate and thermal conductance. Most of the variability in these characteristics was found to be explained by body mass, followed by temperature characteristics of climate, but not precipitation, of the species distributional ranges. This analysis shows that the naked mole-rat is comparable to the other mole-rat species in these physiological characteristics.

The paper is devoted to analyzing consistent individual differences in behavior, also known as “personalities,” in the context of a vital ant task—the detection and transportation of food. I am trying to elucidate the extent to which collective cognition is individual-based and whether a single individual’s actions can suffice to direct the entire colony or colony units. The review analyzes personalities in various insects with different life cycles and provides new insights into the role of individuals in directing group actions in ants. Although it is widely accepted that, in eusocial insects, colony personality emerges from the workers’ personalities, there are only a few examples of investigations of personality at the individual level. The central question of the review is how the distribution of behavioral types and cognitive responsibilities within ant colonies depends on a species’ foraging style. In the context of how workers’ behavioral traits display during foraging, a crucial question is what makes an ant a scout that discovers a new food source and mobilizes its nestmates. In mass recruiting, tandem-running, and even in group-recruiting species displaying leadership, the division of labor between scouts and recruits appears to be ephemeral. There is only little, if any, evidence of ants’ careers and behavioral consistency as leaders. Personal traits characterize groups of individuals at the colony level but not performers of functional roles during foraging. The leader-scouting seems to be the only known system that is based on a consistent personal difference between scouting and foraging individuals.

Convergent evolution of eusociality with the division of reproduction and its plastic transition in Hymenoptera has long attracted the attention of researchers. To explain the evolutionary scenario of the reproductive division of labor, several hypotheses had been proposed. Among these, we focus on the most basic concepts, i.e., the ovarian ground plan hypothesis (OGPH) and the split-function hypothesis (SFH). The OGPH assumes the physiological decoupling of ovarian cycles and behavior into reproductive and non-reproductive individuals, whereas the SFH assumes that the ancestral reproductive function of juvenile hormone (JH) became split into a dual function. Here, we review recent progress in the understanding of the neurohormonal regulation of reproduction and social behavior in eusocial hymenopterans, with an emphasis on biogenic amines. Biogenic amines are key substances involved in the switching of reproductive physiology and modulation of social behaviors. Dopamine has a pivotal role in the formation of reproductive skew irrespective of the social system, whereas octopamine and serotonin contribute largely to non-reproductive social behaviors. These decoupling roles of biogenic amines are seen in the life cycle of a single female in a solitary species, supporting OGPH. JH promotes reproduction with dopamine function in primitively eusocial species, whereas it regulates non-reproductive social behaviors with octopamine function in advanced eusocial species. The signal transduction networks between JH and the biogenic amines have been rewired in advanced eusocial species, which could regulate reproduction in response to various social stimuli independently of JH action.

Social information is widely used in the animal kingdom and can be highly adaptive. In social insects, foragers can use social information to find food, avoid danger, or choose a new nest site. Copying others allows individuals to obtain information without having to sample the environment. When foragers communicate information they will often only advertise high-quality food sources, thereby filtering out less adaptive information. Stingless bees, a large pantropical group of highly eusocial bees, face intense inter- and intra-specific competition for limited resources, yet display disparate foraging strategies. Within the same environment there are species that communicate the location of food resources to nest-mates and species that do not. Our current understanding of why some species communicate foraging sites while others do not is limited. Studying freely foraging colonies of several co-existing stingless bee species in Brazil, we investigated if recruitment to specific food locations is linked to 1) the sugar content of forage, 2) the duration of foraging trips, and 3) the variation in activity of a colony from 1 day to another and the variation in activity in a species over a day. We found that, contrary to our expectations, species with recruitment communication did not return with higher quality forage than species that do not recruit nestmates. Furthermore, foragers from recruiting species did not have shorter foraging trip durations than those from weakly recruiting species. Given the intense inter- and intraspecific competition for resources in these environments, it may be that recruiting species favor food resources that can be monopolized by the colony rather than food sources that offer high-quality rewards.

Research on sociality in marine fishes is a vibrant field that is providing new insights into social evolution more generally. Here, we review the past two decades of research, identifying knowledge gaps and new directions. Two coral reef fishes, with social systems similar to other cooperative breeders, have emerged as models: the clown anemonefish Amphiprion percula and the emerald goby Paragobiodon xanthosoma. In these systems, non-breeders do not forgo their own reproduction to gain indirect genetic benefits. Rather, they do so because they stand to inherit the territory in the future and there are strong ecological and social constraints. The reasons why breeders tolerate non-breeders remain obscure, though it is plausibly a combination of weak kin selection, bet-hedging, and benefits mediated via mutualistic interactions with cnidarian hosts. The latter is particularly interesting, given the parallels with other social animals with mutualistic partners, such as acacia ants. Looking beyond the two model species, our attention is turning to species with more complex social organization, such as the damselfish Dascyllus aruanus. Here, variable group stability, conflict intensity, and reproductive skew provide opportunities to test theories of social evolution that have only been tested in a few taxa. New methods like social network analysis are enabling us to uncover more subtle effects of ecology on social interactions. More recently, comparative methods have yielded insights into the correlates of interspecific variation in sociality in the genera to which our model species belong. Phylogenetically controlled contrasts within the genus Gobiodon, have revealed the role of ecology, life history traits, and their interaction in sociality: smaller bodied species are more social than larger bodied species, which are only social on large corals. As climate change affects coral reefs, there is a pressing need to understand the many ways in which environmental disturbance influences these unique social systems. In sum, coral reef fishes have enabled us to test the robustness of current theories of social evolution in new taxa and environments, and they have generated new insights into social evolution that are applicable to a wider variety of taxa.

Stable social groups usually consist of families. However, recent studies have revealed higher level social structure, with interactions between family groups across different levels of social organization in multiple species. The explanations for why this apparently paradoxical behaviour arises appear to be varied and remain untested. Here, we use automated radio-tagging data from over 1000 wasps from 93 nests and social network analyses of over 30 000 nest visitation records to describe and explain interactions across levels of social organization in the eusocial paper wasp Polistes canadensis . We detected three levels of social organization (nest, aggregation and community) which exchange ‘drifter’ individuals within and between levels. The highest level (community) may be influenced by the patchiness of high-quality nesting habitats in which these insects exist. Networks of drifter movements were explained by the distance between nests, the group size of donor nests and the worker-to-brood ratios on donor and recipient nests. These findings provide some explanation for the multi-level social interactions, which may otherwise seem paradoxical. Fitness benefits across multiple levels of social organization should be considered when trying to understand animal societies.

In eusocial insects, particularly in ants, caste differentiation is extremely complicated when we rely on traditional taxonomy. In most species, the worker caste does not display any distinct morphological characters neither the caste’s central division according to their morphological size variations. We used a landmark-based geometric morphometric approach to quantify the morphological characteristics of female caste systems (queen, major and minor worker ant) of Oecophylla smaragdina. Our findings suggested that each caste has its unique shape and size. Especially in the worker caste, apart from the size variations, we can use the shape as a prominent tool for distinguishing between them. The O. smaragdina exhibits a triphasic allometry pattern. Studying the allometry and non-allometry components of each caste system revealed a highly complex size and shape relationship in the female caste systems. From the allometric and non-allometric analysis, we concluded that the major worker ants showed a closer relationship with the queen than the minor worker ant. This outcome demonstrated that Asian weaver ant exhibits complex shape variations related to size and is correlated to their functional modular characters. This research sheds new light on caste systems’ taxonomic uncertainties for eusocial hymenopteran groups, especially ants.

A central goal in evolutionary biology is to determine the predictability of adaptive genetic changes. Despite many documented cases of convergent evolution at individual loci, little is known about the repeatability of gene family expansions and contractions. To address this void, we examined gene family evolution in the redheaded pine sawfly Neodiprion lecontei, a non-eusocial hymenopteran and exemplar of a pine-specialized lineage evolved from angiosperm-feeding ancestors. After assembling and annotating a draft genome, we manually annotated multiple gene families with chemosensory, detoxification, or immunity functions and characterized their genomic distributions and evolutionary history. Our results suggest that expansions of bitter gustatory receptor (GR), clan 3 cytochrome P450 (CYP3), and antimicrobial peptide (AMP) subfamilies may have contributed to pine adaptation. By contrast, there was no evidence of recent gene family contraction via pseudogenization. Next, we compared the number of genes in these same families across insect taxa that vary in diet, dietary specialization, and social behavior. In Hymenoptera, herbivory was associated with small GR and olfactory receptor (OR) families, eusociality was associated with large OR and small AMP families, and—unlike investigations in more closely related taxa—ecological specialization was not related to gene family size. Overall, our results suggest that gene families that mediate ecological interactions may expand and contract predictably in response to particular selection pressures, however, the ecological drivers and temporal pace of gene gain and loss likely varies considerably across gene families.

Eusocial insects exhibit reproductive division of labor, in which only a part of colony members differentiates into reproductives. In termite colonies, the division of labors is performed among multiple types of individuals (i.e., castes), such as reproductives, workers, and soldiers to organize their society. Caste differentiation occurs according to extrinsic factors, such as social interactions, leading to developmental modifications during postembryonic development, and consequently, the caste ratio in a colony is appropriately coordinated. In particular, when the current reproductives die or become senescent, some immature individuals molt into supplementary reproductives, also known as “neotenics,” that take over the reproductive task in their natal colony. Neotenics exhibit variety of larval features, such as winglessness, and thus, immature individuals are suggested to differentiate by a partial release from arrested development, particularly in the reproductive organs. These neotenic features, which have long been assumed to develop via heterochronic regulation, provide us opportunities to understand the developmental mechanisms and evolutionary origin of the novel caste. This article overviews the accumulated data on the physiological and developmental mechanisms that regulate the neotenic differentiation in termites. Furthermore, the evolutionary trajectories leading to neotenic differentiation are discussed, namely the acquisition of a regulatory mechanism that enable the partial release from a developmentally arrested state.

Arthropods can produce a wide range of antifungal compounds, including specialist proteins, cuticular products, venoms and haemolymphs. In spite of this, many arthropod taxa, particularly eusocial insects, make use of additional antifungal compounds derived from their mutualistic association with microbes. Because multiple taxa have evolved such mutualisms, it must be assumed that, under certain ecological circumstances, natural selection has favoured them over those relying upon endogenous antifungal compound production. Further, such associations have been shown to persist versus specific pathogenic fungal antagonists for more than 50 million years, suggesting that compounds employed have retained efficacy in spite of the pathogens' capacity to develop resistance. We provide a brief overview of antifungal compounds in the arthropods’ armoury, proposing a conceptual model to suggest why their use remains so successful. Fundamental concepts embedded within such a model may suggest strategies by which to reduce the rise of antifungal resistance within the clinical milieu.

Termite colonies, composed of large numbers of siblings, develop an important caste-based division of labor; individuals in these societies interact via intra- or intercaste chemical communications. For more than 50 years, termites have been known to use a variety of pheromones to perform tasks necessary for maintenance of their societies, similar to eusocial hymenopterans. Although trail-following pheromones have been chemically identified in various termites, other types of pheromones have not been elucidated chemically or functionally. In the past decade, however, chemical compositions and biological functions have been successfully identified for several types of termite pheromones; accordingly, the details of the underlying pheromone communications have been gradually revealed. In this review, we summarize both the functions of all termite pheromones identified so far and the chemical interactions among termites and other organisms. Subsequently, we argue how termites developed their sophisticated pheromone communication. We hypothesize that termites have diverted defensive and antimicrobial substances to pheromones associated in caste recognition and caste-specific roles. Furthermore, termites have repeatedly used a pre-existing pheromone or have added supplementary compounds to it in accordance with the social context, leading to multifunctionalization of pre-existing pheromones and emergence of new pheromones. These two mechanisms may enable termites to transmit various context-dependent information with a small number of chemicals, thus resulting in formation of coordinated, complex, and rational chemical communication systems.

Despite the outstanding diversity and ecological relevance of social insects in most terrestrial ecosystems, current knowledge of these insects in the Atlantic Forest is still somewhat dispersed in literature. In this chapter, we offer an overview covering the origin, evolution, diversity, functional composition, and distribution of all the eusocial species of ants, bees, wasps (Hymenoptera), and termites (Blattaria, Isoptera) known to occur in the Atlantic Forest. We compiled a database consisting of 1401 species distributed in 189 genera of the two insect orders assessed here. A total of 1250 species of social hymenopterans and 151 species of termites were here recorded for the Atlantic Forest. Additionally, we update the information regarding the state of knowledge, diversity gaps, and prospects for the eusocial insects of the Atlantic Forest. Considering the impressive richness presented in this compilation and the crucial role of social insects in the main ecological processes on Atlantic rainforest landscape, it became urgent to target those organisms in conservation actions and research. A thoughtful study on current, past, and future species distribution of social insects in the Atlantic Forest could indicate priority areas for conservation and endangered species in different scales, including in face of climate change.