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Sexual dimorphism, the phenotypic differences between males and females within a species, is widespread in the animal kingdom. This study investigates the extent of sexual dimorphism and species divergence in external morphology in two closely related freshwater fish species, Devario malabaricus and D. micronema, in Sri Lanka. Devario malabaricus, a habitat generalist, inhabits a wide range of aquatic environments, while D. micronema, a habitat specialist, resides in shaded rainforest streams. The study reveals size differences between the two species: D. malabaricus is consistently larger than D. micronema. However, there are no size differences between the sexes within each species. Several additional morphological traits, such as head length, interorbital width, predorsal length and postdorsal length display divergence between the species as well as between the sexes within each species; these patterns are also consistent across populations. The sexually dimorphic traits are similar between the two species despite their distinct ecological habitats. However, Devario malabaricus exhibit stronger sexual dimorphism compared to D. micronema, supporting the prediction of a positive relationship between the extent of sexual dimorphism and ecological generalism. The study highlights the importance of considering sexual dimorphism in morphometric comparisons in taxonomic studies of Devario and suggests that divergent selection between the sexes contributes to morphological variation in this group. [ABSTRACT FROM AUTHOR]

Sexual selection has been suggested to influence the expression of male behavioral consistency. However, despite predictions, direct experimental support for this hypothesis has been lacking. Here, we investigated whether sexual selection altered male behavioral consistency in Drosophila melanogaster —a species with both pre- and postcopulatory sexual selection. We took 1,144 measures of locomotor activity (a fitness-related trait in D. melanogaster) from 286 flies derived from replicated populations that have experimentally evolved under either high or low levels of sexual selection for >320 generations. We found that high sexual selection males were more consistent (decreased within-individual variance) in their locomotor activity than male conspecifics from low sexual selection populations. There were no differences in behavioral consistency between females from the high and low sexual selection populations. Furthermore, while females were more behaviorally consistent than males in the low sexual selection populations, there were no sex differences in behavioral consistency in high sexual selection populations. Our results demonstrate that behavioral plasticity is reduced in males from populations exposed to high levels of sexual selection. Disentangling whether these effects represent an evolved response to changes in the intensity of selection or are manifested through nongenetic parental effects represents a challenge for future research. [ABSTRACT FROM AUTHOR]

Choosing a romantic partner for a long-term relationship is one of the most significant decisions one makes during our lifetime. We have inherited an evolved framework from our ancestors that contains traits, as well as preferences for these traits, to solve this task. We use this framework consciously or unconsciously to choose prospective romantic partners. Following this reasoning, sexual strategy theory (SST) has been proposed for predicting which traits women and men prefer in a romantic partner for a long-term relationship. These predictions were empirically tested in the current work based on a sample of 1193 Norwegian adolescents who responded to an online questionnaire. We implemented the study hypotheses, derived from SST, in three statistical models, which were tested using structural equation modeling. In brief, our results revealed that women only valued resources more than men when we controlled for materialistic traits. This finding contrasts with SST's prediction that women would value resources more than men, independently of other variables. As for the second prediction that men value physical attractiveness more than women, this pattern existed universally and was independent of, for instance, how egalitarian they were. We thus conclude that SST was only partially supported and that variables that may reflect societal circumstances (e.g., wealth, gender, equality) should be considered when examining the mate choice behavior of women and men. The theoretical and practical implications of the study are also discussed. [ABSTRACT FROM AUTHOR]

Individuals delay natal dispersal for many reasons. There may be no place to disperse to; immediate dispersal or reproduction may be too costly; immediate dispersal may mean that the individual and their relatives miss the benefits of group living. Understanding the factors that lead to the evolution of delayed dispersal is important because delayed dispersal sets the stage for complex social groups and social behavior. Here, we study the evolution of delayed dispersal when the quality of the local environment is improved by greater numbers of individuals (e. g. , safety in numbers). We assume that individuals who delay natal dispersal also expect to delay personal reproduction. In addition, we assume that improved environmental quality benefits manifest as changes to fecundity and survival. We are interested in how do the changes in these life-history features affect delayed dispersal. We use a model that ties evolution to population dynamics. We also aim to understand the relationship between levels of delayed dispersal and the probability of establishing as an independent breeder (a population-level feature) in response to changes in life-history details. Our model emphasizes kin selection and considers a sexual organism, which allows us to study parent–offspring conflict over delayed dispersal. At evolutionary equilibrium, fecundity and survival benefits of group size or quality promote higher levels of delayed dispersal over a larger set of life histories with one exception. The exception is for benefits of increased group size or quality reaped by the individuals who delay dispersal. There, the increased benefit does not change the life histories supporting delay dispersal. Next, in contrast to previous predictions, we find that a low probability of establishing in a new location is not always associated with a higher incidence of delayed dispersal. Finally, we find that increased personal benefits of delayed dispersal exacerbate the conflict between parents and their offspring. We discuss our findings in relation to previous theoretical and empirical work, especially work related to cooperative breeding. • We study the evolution of delayed natal dispersal. • We assume delayed dispersal brings benefits to the natal group. • The number of delayed-dispersers is independent of the group quality. • Habitat saturation is not always associated with delayed dispersal. • Increased group benefits exacerbate conflict within the natal group. [ABSTRACT FROM AUTHOR]

Otherwise, apparently cryptic mammals often have conspicuous patches of colour on distal regions of their body, possibly for signalling. To investigate ideas about communication within sociosexual contexts, we used a comparative dataset for 2726 terrestrial mammals to match the coloration and patterning of distal body areas (head, chest, rump and tail) to activity cycle, group size, sexual size dimorphism, mating system and congener overlap at both Class and Order levels. Using phylogenetic controls, we uncovered repeated associations between white colour patches and nocturnality, conspicuous rump patches and sexual selection and multicoloured, complex patterning on distal regions of the body being associated with small group size. Overall, however, we found rather few associations between conspicuous coloration and behavioural, social and morphological variables, suggesting that visual signalling is not a key driver of communication in mammals, perhaps because the majority are nocturnal and solitary, and rely on olfactory signalling. [ABSTRACT FROM AUTHOR]

Understanding the connection between personality and fitness is an important topic in both behavioural and evolutionary ecology. Most of our current knowledge stems from lab-studies despite that studies in natural populations for most parts generate more ecologically relevant information on behavioural variation and mating success. Here, we quantified Calopteryx splendens male mating success across two behavioural axes: courtship and boldness-aggression, testing personality and plasticity of behavioural traits in a natural population situated in the central-core of the species distribution. We also measured wing patch area and body size as these traits are important in damselfly sexual selection. The only behavioural trait that positively affected mating success was consistency in courtship effort. Among morphological traits, smaller wing patch size was associated with greater male mating success, while thorax size was a better predictor of male mating success than either personality or plasticity in boldness and activity. Our results demonstrate the importance of behavioural consistency over plasticity in a wild insect population and support prior studies showing the importance of body size for mating success. [ABSTRACT FROM AUTHOR]

Biologists have long wondered how sexual ornamentation influences a species' risk of extinction. Because the evolution of condition‐dependent ornamentation can reduce intersexual conflict and accelerate the fixation of advantageous alleles, some theory predicts that ornamented taxa can be buffered against extinction in novel and/or stressful environments. Nevertheless, evidence from the wild remains limited. Here, we show that ornamented dragonflies are less vulnerable to extinction across multiple spatial scales. Population‐occupancy models across the Western United States reveal that ornamented species have become more common relative to non‐ornamented species over >100 years. Phylogenetic analyses indicate that ornamented species exhibit lower continent‐wide extinction risk than non‐ornamented species. Finally, spatial analyses of local dragonfly assemblages suggest that ornamented species possess advantages over non‐ornamented taxa at living in habitats that have been converted to farms and cities. Together, these findings suggest that ornamented taxa are buffered against contemporary extinction at local, regional, and continental scales. [ABSTRACT FROM AUTHOR]

The evolution of behavioral isolation is often the first step toward speciation. While past studies show that behavioral isolation will sometimes evolve as a by-product of divergent ecological selection, we lack a more nuanced understanding of factors that may promote or hamper its evolution. The environment in which mating occurs may be important in mediating whether behavioral isolation evolves for two reasons. Ecological speciation could occur as a direct outcome of different sexual interactions being favored in different mating environments. Alternatively, mating environments may vary in the constraint they impose on traits underlying mating interactions, such that populations evolving in a "constraining" mating environment would be less likely to evolve behavioral isolation than populations evolving in a less constraining mating environment. In the latter, mating environment is not the direct cause of behavioral isolation but rather permits its evolution only if other drivers are present. We test these ideas with a set of 28 experimental fly populations, each of which evolved under one of two mating environments and one of two larval environments. Counter to the prediction of ecological speciation by mating environment, behavioral isolation was not maximal between populations evolved in different mating environments. Nonetheless, mating environment was an important factor as behavioral isolation evolved among populations from one mating environment but not among populations from the other. Though one mating environment was conducive to the evolution of behavioral isolation, it was not sufficient: assortative mating only evolved between populations adapting to different-larval environments within that mating environment, indicating a role for ecological speciation. Intriguingly, the mating environment that promoted behavioral isolation is characterized by less sexual conflict compared to the other mating environment. Our results suggest that mating environments play a key role in mediating ecological speciation via other axes of divergent selection. [ABSTRACT FROM AUTHOR]

The breeder's equation, Δ z ¯ = G β   ⁠ , allows us to understand how genetics (the genetic covariance matrix, G) and the vector of linear selection gradients β interact to generate evolutionary trajectories. Estimation of β using multiple regression of trait values on relative fitness revolutionized the way we study selection in laboratory and wild populations. However, multicollinearity, or correlation of predictors, can lead to very high variances of and covariances between elements of β , posing a challenge for the interpretation of the parameter estimates. This is particularly relevant in the era of big data, where the number of predictors may approach or exceed the number of observations. A common approach to multicollinear predictors is to discard some of them, thereby losing any information that might be gained from those traits. Using simulations, we show how, on the one hand, multicollinearity can result in inaccurate estimates of selection, and, on the other, how the removal of correlated phenotypes from the analyses can provide a misguided view of the targets of selection. We show that regularized regression, which places data-validated constraints on the magnitudes of individual elements of β , can produce more accurate estimates of the total strength and direction of multivariate selection in the presence of multicollinearity and limited data, and often has little cost when multicollinearity is low. We also compare standard and regularized regression estimates of selection in a reanalysis of three published case studies, showing that regularized regression can improve fitness predictions in independent data. Our results suggest that regularized regression is a valuable tool that can be used as an important complement to traditional least-squares estimates of selection. In some cases, its use can lead to improved predictions of individual fitness, and improved estimates of the total strength and direction of multivariate selection. [ABSTRACT FROM AUTHOR]

Simple Summary: Historically, researchers' biases about male and female behavior have affected the study of mate choice (animals' selective responses to certain sexual partners over others), and female mate choice has often been dismissed as unimportant. In this study, we investigated whether female blue monkeys could exercise mate choice successfully by siring offspring with their preferred males. Blue monkeys generally live in a one-male multi-female social organization, but multiple males may join the group during the breeding season. Female blue monkeys, thus, have access to multiple potential mates, and initiate sexual interactions more than males, making them an appropriate species in which to study female choice. We found that a female's most preferred male was most likely to be the father of her infant, even if he was not a consistent group member. Though competition between males may still influence paternity outcomes, these results suggest that blue monkey females can exercise mate choice successfully, even in a social organization that would seem to favor male control. Female mate choice may drive sexual selection, but discerning whether female behaviors reflect free expression of choice or responses to constraints can be difficult. We investigated the efficacy of female choice in wild blue monkeys using 10 years of behavior and paternity data (N = 178 male–female dyads). Although blue monkeys live modally in one-male polygynous groups, where male-biased intersexual power is expected, females can access multiple potential mates during seasonal male influxes and occasional intergroup encounters. Additionally, extra-group males sire offspring. We examined female resistance rates to male-initiated sexual interactions, and unsolicited proceptive behavior that females directed to males (corrected for male availability). Females seldom resisted male solicitation, but initiated sexual interactions more than males. Females generally preferred residents. Those who preferred non-residents tended to have residents with longer tenures, but neither female parity nor rank influenced the tendency to prefer non-residents vs. residents. The male most solicited by a particular female fathered that female's infant 82% of the time; odds of siring were 26 times higher for most vs. nonpreferred males. Female preference predicted paternity even more strongly among non-resident males, with odds of siring 33 times higher for most vs. nonpreferred non-residents. Neither female rank nor parity influenced her likelihood of having her preferred partner as sire. Paternity by preferred males did not affect infant survival. While we cannot fully discount the effect of male–male competition on paternity, these results suggest that blue monkey females can exercise choice successfully, even in a polygynous mating system. [ABSTRACT FROM AUTHOR]

Understanding the evolution of traits subject to trade-offs is challenging because phenotypes can (co)vary at both the among- and within-individual levels. Among-individual covariation indicates consistent, possibly genetic, differences in how individuals resolve the trade-off, while within-individual covariation indicates trait plasticity. There is also the potential for consistent among-individual differences in behavioral plasticity, although this has rarely been investigated. We studied the sources of (co)variance in two characteristics of an acoustic advertisement signal that trade-off with one another and are under sexual selection in the gray treefrog, Hyla chrysoscelis : call duration and call rate. We recorded males on multiple nights calling spontaneously and in response to playbacks simulating different competition levels. Call duration, call rate, and their product, call effort, were all repeatable both within and across social contexts. Call duration and call rate covaried negatively, and the largest covariance was at the among-individual level. There was extensive plasticity in calling with changes in social competition, and we found some evidence for among-individual variance in call rate plasticity. The significant negative among-individual covariance in trait values is perpendicular to the primary direction of sexual selection in this species, indicating potential limits on the response to selection. [ABSTRACT FROM AUTHOR]

Bird song is a classic example of a sexually selected trait, but much of the work relating individual song components to fitness has not accounted for song typically being composed of multiple, often-correlated components, necessitating a multivariate approach. We explored the role of sexual selection in shaping the complex male song of house wrens (Troglodytes aedon) by simultaneously relating its multiple components to fitness using multivariate selection analysis, which is widely used in insect and anuran studies but not in birds. The analysis revealed significant variation in the form and strength of selection acting on song across different selection episodes, from nest-site defense to recruitment of offspring to the breeding population. Males that sang more song typically employed in close communication sired more offspring that were subsequently recruited to the breeding population than those that sang more far-communication song. However, this relationship was not consistent across earlier selection episodes, as evidenced by non-linear selection acting on these song components in other contexts. Collectively, our results present a complex picture of multivariate selection on male song structure that would not be evident using univariate approaches and suggest possible trade-offs within and among song components at different points of the breeding season. [ABSTRACT FROM AUTHOR]

Sexual selection theory predicts that females prefer males in good condition because mating with them provides more resources such as sperm, ejaculates and nuptial gifts. The female's condition also affects her mating decisions, and condition‐dependent mate choice may allow her to gain more resources from a mate in the context of fluctuating resource availability.We here investigated how female mating decisions and their fitness consequences varied in the assassin bug Amphibolus venator when the conditions of potential mates and/or the females differed (good or poor condition).Females in both good and poor conditions preferred males in good condition, and females that mated with males in good condition produced more eggs with higher hatch rates. This increase in fitness may be attributed to the males in good condition transferring more ejaculate to the females.In contrast, female mate preference, fecundity and hatch rates were not affected by their own condition. This suggests that females do not choose mates according to their own condition in A. venator. However, the females in good condition laid larger eggs than females in poor condition, implying that females in good condition may invest more per egg to improve their reproductive success.To understand the evolution of female mate choice, it is necessary to investigate the effects of the condition of both sexes on female mating decision and their fitness. In A. venator, male condition may affect mate choice more than female condition. [ABSTRACT FROM AUTHOR]

Passerines are the most successfully diversified bird order (around 60% of all avian species). They have developed complicated songs to defend their territories and to attract females for mating that can evolve quickly due to cultural transmission. Complex singing as well as plumage coloration of male birds are honest signals for potential partners and provide information about the males' quality. To function as honest signals, both traits must be costly for the males. Of course, not all passerine species are equally clever or beautiful. Even within a single family of 50 to 70 species, relevant traits may vary considerably. Tits and chickadees (Paridae) comprise species of similar size, varying a lot in coloration and plumage pattern. The territorial songs are relatively short and simple. We investigated the relationship between song complexity and plumage coloration, taking phylogenetic relationships into account. We studied 55 out of the 64 species with 1084 song recordings retrieved from an online database. In the best model, besides colorfulness, body size had a negative impact on song complexity. Large colorful species were found to sing less complex songs. This result supports the hypothesis of a trade-off between costly traits and their likely intense signal function. This study contributes to a better understanding of how sexual selection influences the diversification of traits. In addition, we found that despite the relatively uniform size, the general negative correlation between body size and song frequency can be recovered. Some song traits are further influenced by distribution and thus by interspecific differences in climate niche. [ABSTRACT FROM AUTHOR]

Social learning is a mechanism used by many species to efficiently gain information about their environment. Although many animals live in an environment where members of other species are present, little is known about interspecific social learning. Domesticated and urbanized species provide the opportunity to investigate whether nonhuman animals can learn from heterospecifics such as humans, who are integral parts of their social landscape. Although domestic dogs Canis familiaris have been intensively researched for their ability to learn from humans, most studies have focused on dogs living as pets. However, free-ranging dogs represent the majority of the world's dog population, they live alongside humans, scavenge on human refuse, and are subject to natural and sexual selection. Thus, free-ranging dogs with extensive exposure to humans and their artifacts provide the opportunity to investigate interspecific social learning in a naturalistic setting, where learning from humans might be a benefit for them. Here we tested individual free-ranging dogs in a between-subject design: Dogs in the control group could spontaneously choose between two novel and differently patterned food-delivering boxes. In the experimental group, instead, dogs could first observe an unfamiliar human approaching and eating from 1 of the 2 boxes. We provide the first evidence that free-ranging dogs match the choice of an unfamiliar human. These results show that at least simple forms of interspecific social learning might be involved in dogs' success in living alongside humans in a complex urbanized environment. [ABSTRACT FROM AUTHOR]

Inter-sexual mate competition occurs any time opposite-sex individuals simultaneously seek to acquire or maintain exclusive access to the same sexual partner. This underappreciated form of mate competition has been anecdotally documented in several avian and mammalian species, and systematically described among Japanese macaques and humans. Here, we extend the concept of inter-sexual mate competition by reassessing a remarkable series of Portuguese letters, penned in 1664 and later discovered and translated by Mott and Assunção (J Homosex 16:91–104, 1989). The letters comprise one side of a correspondence between two males, former lovers who were scrutinized by the Portuguese Inquisition. After ending the relationship, the recipient of the letters was betrothed to a woman, which provoked a jealous response from his jilted male lover and pleas to reunite. We argue that the letters portray a prolonged sequence of inter-sexual mate competition in which a male and female competitor vied for the same man. An established taxonomy of mate competition tactics was applied to the behavior of both competitors illustrating many parallels with contemporary examples of inter-sexual mate competition. Through this comparison, we show that modern mate competition taxonomies can be fruitfully applied to historical texts and that inter-sexual mate competition occurred hundreds of years before the present. Other examples of inter-sexual mate competition are likely to exist in the historical record, providing a rich source of scientific information if appropriate theoretical frameworks are employed. Indeed, any time individuals are attracted to sexual partners who behave in a bisexual manner, then inter-sexual mate competition can ensue with members of the other sex. [ABSTRACT FROM AUTHOR]

We analysed the influence of laboratory domestication, under relaxed conditions, on the courtship behaviour of the fruit fly species Anastrepha obliqua, an important agricultural pest. We compared the temporal patterns of pheromone emission (Calling behaviour) and the frequencies and sequences of the courtship behavioural units of males of a laboratory lineage and a wild lineage. Our results indicated similarities in the temporal behavioural patterns of calling, the durations of their behavioural sequences, the final sequences of courtships resulting in copulation, of wild and laboratory males. Differences, however, were observed between the two populations in terms of the frequencies of the behavioural units executed and the initial sequence of courtship. Differences were noted in the presence or absence of some behavioural units within the courtship behavioural repertoires of the laboratory‐reared and wild. The wild males did not show units such as Alignment, Contact, Fighting and Marking Leaf that were observed in the laboratory males' courtship behaviour under laboratory conditions; on the other hand, laboratory males did not show the Abdominal movements and Oscillation observed in the courtship behaviour of wild males. The rearing of A. obliqua males under relaxed conditions in the laboratory provides an environment adequate for the preservation of behavioural characteristics relevant to the successful mating, such as Movement, Arrowhead 1, and Attempt, and in temporal patterns of pheromone emission. [ABSTRACT FROM AUTHOR]

Primate mandibular morphology is often associated with jaw functionality of the masticatory complex in the context of variation in diets. Recent research into the disparities between the diet and jaw functionality in male and female hominoids is inconclusive and suggests that sexual dimorphism in the mandible may be influenced by external factors such as temporalis and masseter muscle morphology, which in turn may be influenced by sexual selection. As the muscles associated with mastication (i.e., the type of chewing exhibited by primates and other mammals) encompass the mandible as well as the neurocranium, including the sagittal crest among some individuals, this study investigates sex‐specific associations between regions of the mandibular ramus and neurocranium associated with mastication in a dentally mature sample of Gorilla and Pongo. A total of four cranial and mandibular variables were measured in two Gorilla taxa (Gorilla gorilla gorilla and Gorilla beringei graueri) and one Pongo taxon (Pongo pygmaeus pygmaeus) (n = 220). For all three taxa, we investigate (a) whether the degree of sexual dimorphism in cranial regions associated with sagittal cresting (sagittal crest size (SCS) and temporalis muscle attachment area (TMAA)) is proportional to the degree of mandibular ramus area (MRA) and coronoid process height (CPH) sexual dimorphism, (b) whether there are sex differences in scaling relationships between TMAA and MRA, and (c) whether there are sex differences in the strength of association between TMAA and CPH. We show that for G. g. gorilla, variables associated with sagittal cresting show higher sexual dimorphism values than our two mandibular ramus variables, which is not the case for G. b. graueri or for P. p. pygmaeus. All three taxa show similar sex‐specific scaling relationships between TMAA and MRA, where for males this relationship does not diverge from isometry, and for females there is a negative allometric relationship. Our findings also show intraspecific sex differences in allometric slopes between MRA and TMAA for all three taxa. Only G. g. gorilla shows a significant association between TMAA and CPH, which is observed in both sexes. Although there are some statistical associations between the cranial and mandibular regions associated with mastication, our results show that among male gorillas and orangutans, patterns of variation in the sagittal crest, TMAA, mandibular ramus and the coronoid process cannot be explained by the muscle attachment hypothesis alone. These findings have implications surrounding the associations between social behaviour and the morphology of the craniofacial complex. [ABSTRACT FROM AUTHOR]

Copulatory organs are a key trait in reproductive compatibility and sexual isolation. The role of male genitalia in boosting mating success is well known and is often the outcome of behavioural and biological constraints, although no clear and common interpretation about their evolution appears broadly applicable. In snakes, hemipenial morphology has often been described under the perspective of sexual selection, taking into consideration both behavioural and morphological traits of both sexes. We investigated hemipenial morphology and ornamentation in the two subspecies of Hierophis viridiflavus, a male-male combating colubrid, and compared it to the sister species H. gemonensis, to assess intraspecific variation in size of genitalia and ornamentation richness. The male intromitted organ of this species is unilobed and bulbous, with rich ornamentations consisting of basal spines and apical calyculations. We detected no statistically significant difference in hemipenial size, basal spine count, and spine length between the two subspecies, suggesting that no copulatory barrier is present between the two clades. Although hemipenial morphology and anatomy do not seem suitable to assess intraspecific variability as shown in this study, they are often highly variable at the family or genus level, suggesting that the evolution of male genitalia is linked to phylogenetic relationships and that hemipenial divergence might be correlated to lineage splitting despite not being necessarily the main cause. Future studies should be aimed at investigating hemipenial morphology and anatomy across species under the perspective of comparative phylogeny and reproductive behaviours to address thoroughly the constraints of hemipenial evolution and development. [ABSTRACT FROM AUTHOR]

The Late Cretaceous of western North America supported diverse dinosaur assemblages, though understanding patterns of dinosaur diversity, evolution, and extinction has been historically limited by unequal geographic and temporal sampling. In particular, the existence and extent of faunal endemism along the eastern coastal plain of Laramidia continues to generate debate, and finer scale regional patterns remain elusive. Here, we report a new centrosaurine ceratopsid, Lokiceratops rangiformis, from the lower portion of the McClelland Ferry Member of the Judith River Formation in the Kennedy Coulee region along the Canada-USA border. Dinosaurs from the same small geographic region, and from nearby, stratigraphically equivalent horizons of the lower Oldman Formation in Canada, reveal unprecedented ceratopsid richness, with four sympatric centrosaurine taxa and one chasmosaurine taxon. Phylogenetic results show that Lokiceratops, together with Albertaceratops and Medusaceratops, was part of a clade restricted to a small portion of northern Laramidia approximately 78 million years ago. This group, Albertaceratopsini, was one of multiple centrosaurine clades to undergo geographically restricted radiations, with Nasutuceratopsini restricted to the south and Centrosaurini and Pachyrostra restricted to the north. High regional endemism in centrosaurs is associated with, and may have been driven by, high speciation rates and diversity, with competition between dinosaurs limiting their geographic range. High speciation rates may in turn have been driven in part by sexual selection or latitudinally uneven climatic and floral gradients. The high endemism seen in centrosaurines and other dinosaurs implies that dinosaur diversity is underestimated and contrasts with the large geographic ranges seen in most extant mammalian megafauna. [ABSTRACT FROM AUTHOR]

The popularity of instinct theory—the core of Thorstein Veblen's evolutionary methodology—waned with the rise of behavioral psychology in the 1920s, and resurges with the revival of evolutionary psychology in the 1980s. This study reexamines Charles Darwin's theories of natural and sexual selection within Veblen's theory. By tracing the origin of emulation, this study explores the human struggle for existence at both inter-species and individual levels, enhancing our understanding of Veblen's theory as rooted in Darwinism and reinterpreted within Geoffrey Hodgson's concept of emergence. Differing from Clarence Ayres' dichotomy, analysis resituates Veblen's instinct theory within contemporary evolutionary psychology. [ABSTRACT FROM AUTHOR]

Sexual size dimorphism (SSD) is a widespread phenomenon in the animal world resulting from differential selection on the sexes. The northern pike (Esox lucius) is a freshwater apex predatory fish species that exhibits female-biased SSD, but the degree to which SSD varies among populations and what variables might dictate variation in SSD in this species remain poorly understood. We sought to quantify the degree of variation in SSD among northern pike populations across a large portion of their North American range, as well as evaluate associations between the magnitude of SSD in northern pike populations with environmental variables and life history traits of populations. We quantified SSD in 102 populations of northern pike across the province of Ontario, Canada, using a standardized gillnetting database, and investigated the degree to which both environmental variables (cisco [Coregonus artedi] abundance as catch-per-unit-effort, lake surface area, and latitude) and northern pike life-history traits (early growth and mortality rates) explained variation in female-biased SSD using linear models. Female-biased SSD in mean weight of northern pike increased with increasing cisco abundance, and the difference in female and male mean age increased with increasing latitude. Furthermore, SSD was greater in populations with lower female mortality and early growth rates. These results indicate that slow-growing, long-lived populations of northern pike should exhibit greater female-biased SSD, and that these conditions may be facilitated by the availability of large, energy-dense prey and cooler temperatures at northern latitudes. [ABSTRACT FROM AUTHOR]

Opposite dynamics are behind natural selection and sexual selection. When considering natural and sexual selection separately, the fittest individuals survive. However, when these processes interact, luck often determines the survivor. As a result, chance has a greater impact on evolution. [ABSTRACT FROM AUTHOR]

Bumblebees are phylogenetically related to honey bees and have ecological and economic importance as pollinators of both natural flora and many crops. The mating stage is one of the most important stages in Bombus terrestris (L.) life cycle since it affects diapause success and offspring reproduction. Unlike honey bees, B. terrestris colonies are at higher risk of homozygosity because queens are monandrous. Accordingly, the quality of queens and males, as well as the kinship relationships of individuals, affect mating success much more compared to polyandrous species. In this study, we aimed to investigate sexual selection against inbred mates and inbreeding effects on some mating properties in B. terrestris. The results showed that inbreeding did not cause a significant difference in sexual selection for both queens and males of B. terrestris reared under laboratory conditions. Moreover, there were no significant differences in mating latency and mating duration between related and unrelated couples. Additionally, the weights of queens and males were measured. The results were evaluated, and B. terrestris queens and males were not affected by kinship in the selection of mates during the mating phase. [ABSTRACT FROM AUTHOR]

We investigated post-settlement growth patterns and sexual dimorphism in the carapace, pelon, and cheliped dimensions of the varunid crab Gaetice depressus (De Haan, 1833). We reared crabs in the laboratory from hatching through megalopae to the first to tenth instars, and measurements were made of exuviae or specimens of crabs that successively molted. The males were larger than the females in all instars. The molt increments of carapace width (CW) and carapace length (CL) did not differ between the sexes; the former decreased with growth, especially up to ~3–4 mm, whereas the latter did not change with growth. This may be due to the rapid growth in CW compared to CL during early ontogeny. The proportion of CW to CL was larger in the females than in the males, and the rate of increase in pleon width accelerated greatly after growth to ~4 mm CW. Cheliped dimensions were larger in males than in females, probably as a consequence of sexual selection. Cheliped propodus length and width increased with growth in both sexes, but the rates of increase tended to decelerate after ~7 mm CW in females. This indicates that females may allocate more energy to pleon growth while limiting cheliped growth. [ABSTRACT FROM AUTHOR]

Tourism pressure on the Red Sea ecosystem have posed significant threats to numerous endemic species, including the Ghost Crab Ocypode saratan, which is exclusively found along a small stretch of beach in the Eilat/Aqaba Red Sea Gulf. Due to the limited understanding of their ecology, we investigated how tourism impacts the behavior of this species. Employing a natural setup, we compared burrow dimensions, pyramid structures, and density across three distinct beach sections subjected to varying levels of human interference. Access to a secluded beach, referred to as "No Man's Land," provided a crucial control for our study. This facilitated a comparative analysis of ghost crab activity among beaches experiencing differing levels of human disturbances: (1) a tourist beach characterized by continual high disturbance, (2) a naval beach subject to moderate and sporadic disturbances, and (3) the isolated "no man's land" beach devoid of human presence. Our observations revealed notable differences in ghost crab density among the three beaches. Furthermore, we observed that on the secluded beach, larger individuals tended to establish burrows farther from the waterline and construct taller sand pyramids. Given the significance of sexual selection processes, their conservation becomes imperative for the survival and potential expansion of the ghost crab population across the Gulf of Eilat/Aqaba. We propose a straight-forward and cost-effective strategy: the designation of short, secluded beach enclaves along this gulf. We believe that this approach will mitigate adverse impacts of tourisms while simultaneously benefiting various sandy beach species. [ABSTRACT FROM AUTHOR]

Placerias hesternus, a Late Triassic dicynodont, is one of the last megafaunal synapsids of the Mesozoic. The species has a tusk-like projection on its maxillary bone, known as the caniniform process. This process has been hypothesized to be sexually dimorphic since the 1950s, however this claim has not been thoroughly investigated quantitatively. Here, we examined maxillae, premaxillae, quadrates, and fibulae from a single population from the Placerias Quarry in the Blue Mesa Member of the Chinle Formation, near St. Johns, Arizona, USA to determine if the caniniform process is dimorphic. We made a total of 25 measurements from the four bones and used a maximum likelihood framework to compare the fit of unimodal versus bimodal distributions for each set of measurements. Our results from complete maxillae reveal that the caniniform process has two distinct morphs, with a shorter and longer form. This interpretation is substantiated both by strong statistical support for bimodal distribution of caniniform lengths, and by clustering analysis that clearly distinguishes two morphs for the maxillae. Clustering analysis also shows support for potential dimorphism in the shape of the quadrate. However, no measurements from elements other than the maxilla have a strong likelihood of bimodal distribution. These results support the long-standing hypothesis that the caniniform in Placerias was dimorphic. Alternative explanations to sexual dimorphism that could account for the dimorphism among these fossils include the presence of juveniles in the sample or time-averaged sampling of a chronospecies, but both have been previously rejected for the Placerias Quarry population. The lack of strong dimorphism in non-maxilla elements and increased variation in caniniform length of the large-caniniform morph suggest that the caniniform is a secondary sexual trait, possibly used in intraspecific competition. [ABSTRACT FROM AUTHOR]

Speciation is often driven by selective processes like those associated with viability, mate choice, or local adaptation, and "speciation genes" have been identified in many eukaryotic lineages. In contrast, neutral processes are rarely considered as the primary drivers of speciation, especially over short evolutionary timeframes. Here, we describe a rapid vertebrate speciation event driven primarily by genetic drift. The White Sands pupfish (Cyprinodon tularosa) is endemic to New Mexico's Tularosa Basin where the species is currently managed as two Evolutionarily significant units (ESUs) and is of international conservation concern (Endangered). Whole-genome resequencing data from each ESU showed remarkably high and uniform levels of differentiation across the entire genome (global FST ≈ 0.40). Despite inhabiting ecologically dissimilar springs and streams, our whole-genome analysis revealed no discrete islands of divergence indicative of strong selection, even when we focused on an array of candidate genes. Demographic modeling of the joint allele frequency spectrum indicates the two ESUs split only ~4 to 5 kya and that both ESUs have undergone major bottlenecks within the last 2.5 millennia. Our results indicate the genome-wide disparities between the two ESUs are not driven by divergent selection but by neutral drift due to small population sizes, geographic isolation, and repeated bottlenecks. While rapid speciation is often driven by natural or sexual selection, here we show that isolation and drift have led to speciation within a few thousand generations. We discuss these evolutionary insights in light of the conservation management challenges they pose. [ABSTRACT FROM AUTHOR]

Animal culture evolves alongside genomes, and the two modes of inheritance—culture and genes—interact in myriad ways. For example, stable geographic variation in culture can act as a reproductive barrier, thereby facilitating genetic divergence between "cultural populations." White-crowned sparrows (Zonotrichia leucophrys) are a well-established model species for bird song learning and cultural evolution, as they have distinct, geographically discrete, and culturally transmitted song types (i.e., song dialects). In this study, we tested the hypothesis that divergence between culturally transmitted songs drives genetic divergence within Nuttall's white-crowned sparrows (Z. l. nuttalli). In accordance with sexual selection theory, we hypothesized that cultural divergence between mating signals both preceded and generated genetic divergence. We characterized the population structure and song variation in the subspecies and found two genetically differentiated populations whose boundary coincides with a major song boundary at Monterey Bay, California. We then conducted a song playback experiment that demonstrated males discriminate between songs based on their degree of divergence from their local dialect. These results support the idea that discrimination against non-local songs is driving genetic divergence between the northern and southern populations. Altogether, this study provides evidence that culturally transmitted bird songs can act as the foundation for speciation by sexual selection. [ABSTRACT FROM AUTHOR]

When males compete, sexual selection favors reproductive traits that increase their mating or fertilization success (pre- and postcopulatory sexual selection). It is assumed that males face a trade-off between these 2 types of sexual traits because they both draw from the same pool of resources. Consequently, allocation into mate acquisition or ejaculation should create similar trade-offs with other key life history traits. Tests of these assumptions are exceedingly rare. Males only ejaculate after they mate, and the costs of ejaculation are therefore highly confounded with those of mating effort. Consequently, little is known about how each component of reproductive allocation affects a male's future performance. Here, we ran an experiment using a novel technique to distinguish the life history costs of mating effort and ejaculation for mosquitofish (Gambusia holbrooki). We compared manipulated males (mate without ejaculation), control males (mate and ejaculate), and naïve males (neither mate nor ejaculate) continuously housed with a female and 2 rival males. We assessed their growth, somatic maintenance, mating and fighting behavior, and sperm traits after 8 and 16 weeks. Past mating effort significantly lowered a male's future mating effort and growth, but not his sperm production, while past sperm release significantly lowered a male's future ejaculate quantity, but not his mating effort. Immune response was the only trait impacted by both past mating effort and past ejaculation. These findings challenge the assumption that male reproductive allocation draws from a common pool of resources to generate similar life history costs later in life. Instead, we provide clear evidence that allocation into traits under pre- and postcopulatory sexual selection have different trait-specific effects on subsequent male reproductive performance. Theory assumes that allocation to pre- and post-copulatory sexual traits draws from a common pool of resources, creating equivalent life-history trade-offs. However, this study uses a novel experiment with mosquitofish to reveal independent costs of mating effort and sperm allocation on subsequent male performance. [ABSTRACT FROM AUTHOR]

Infanticide and adoption have been attributed to sexual selection, where an individual later reproduces with the parent whose offspring it killed or adopted. While sexually selected infanticide is well known, evidence for sexually selected adoption is anecdotal. We report on both behaviors at 346 nests over 27 y in green-rumped parrotlets (Forpus passerinus) in Venezuela. Parrotlets are monogamous with long-term pair bonds, exhibit a strongly male-biased adult sex ratio, and nest in cavities that are in short supply, creating intense competition for nest sites and mates. Infanticide attacks occurred at 256 nests in two distinct contexts: 1) Attacks were primarily committed by nonbreeding pairs (69%) attempting to evict parents from the cavity. Infanticide attacks per nest were positively correlated with population size and evicting pairs never adopted abandoned offspring. Competition for limited nest sites was a primary cause of eviction-driven infanticide, and 2) attacks occurred less frequently at nests where one mate died (31%), was perpetrated primarily by stepparents of both sexes, and was independent of population size. Thus, within a single species and mating system, infanticide occurred in multiple contexts due to multiple drivers. Nevertheless, 48% of stepparents of both sexes adopted offspring, and another 23% of stepfathers exhibited both infanticide and long-term care. Stepfathers were often young males who subsequently nested with widows, reaching earlier ages of first breeding than competitors and demonstrating sexually selected adoption. Adoption and infanticide conferred similar fitness benefits to stepfathers and appeared to be equivalent strategies driven by limited breeding opportunities, male-biased sex ratios, and long-term monogamy. [ABSTRACT FROM AUTHOR]

Gamete traits can vary widely among species, populations and individuals, influencing fertilisation dynamics and overall reproductive fitness. Sexual selection can play an important role in determining the evolution of gamete traits with local environmental conditions determining the strength and direction of sexual selection. Here, we test for signatures of post‐mating selection on gamete traits in relation to population density, and possible interactive effects of population density and sperm concentration on sperm motility and fertilisation rates among natural populations of mussels. Our study shows that males from high‐density populations produce smaller sperm compared with males from low‐density populations, but we detected no effect of population density on egg size. Our results also reveal that females from low‐density populations tended to exhibit lower fertilisation rates across a range of sperm concentrations, although this became less important as sperm concentration increased. Variances in fertilisation success were higher for females than males and the effect of gamete compatibility between males and females increases as sperm concentrations increase. These results suggest that local population density can influence gamete traits and fertilisation dynamics but also highlight the importance of phenotypic plasticity in governing sperm–egg interactions in a highly dynamic selective environment. [ABSTRACT FROM AUTHOR]

The existence of adult sexual dimorphism is typically explained as a consequence of sexual selection, yet coevolutionary drivers of sexual dimorphism frequently remain untested. Here, I investigate the role of sexual dimorphism in host–parasite interactions of the brood parasitic diederik cuckoo, Chrysococcyx caprius. Female diederik cuckoos are more cryptic in appearance and pose a threat to the clutch, while male diederik cuckoos are conspicuous and not a direct threat. Specifically, I examine whether sexual dimorphism in diederik cuckoos provokes threat‐level sensitive responses in Southern red bishop, Euplectes orix, hosts. I use experimentally simulated nest intrusions to test whether hosts have the capacity to differentially (i) detect, and/or (ii) discriminate between, male and female diederik cuckoos, relative to harmless controls. Overall, I found no evidence that diederik cuckoos differ in detectability, since both sexes are comparable to controls in the probability and speed of host detection. Furthermore, neither male nor female hosts discriminate between sexually dimorphic diederik cuckoos when engaging in frontline nest defences. However, hosts that witnessed a male diederik cuckoo during the trial were more likely to reject odd eggs. Moreover, experimental eggs were significantly more likely to be rejected when female bishops observed a male compared to a female diederik cuckoo. While the cryptic appearance of female diederik cuckoos does not reduce detection by hosts, it does provide the benefit of anonymity given the egg rejection costs of conspicuous male‐like appearance in the nest vicinity. These findings have implications for the evolution and maintenance of sexual dimorphism across the Cuculidae, and highlight the value of testing assumptions about the ecological drivers of sexual dimorphism. [ABSTRACT FROM AUTHOR]

The mechanisms underlying the divergence of reproductive strategies between closely related species are still poorly understood. Additionally, it is unclear which selective factors drive the evolution of reproductive behavioral variation and how these traits coevolve, particularly during early divergence. To address these questions, we quantified behavioral differences in a recently diverged pair of Nova Scotian three-spined stickleback (Gasterosteus aculeatus) populations, which vary in parental care, with one population displaying paternal care and the other lacking this. We compared both populations, and a full reciprocal F1 hybrid cross, across four major reproductive stages: territoriality, nesting, courtship, and parenting. We identified significant divergence in a suite of heritable behaviors. Importantly, F1 hybrids exhibited a mix of behavioral patterns, some of which suggest sex linkage. This system offers fresh insights into the coevolutionary dynamics of reproductive behaviors during early divergence and offers support for the hypothesis that coevolutionary feedback between sexual selection and parental care can drive rapid evolution of reproductive strategies. [ABSTRACT FROM AUTHOR]

Sexual conflict is believed to be an important evolutionary force driving phenotypic diversification, especially sexual dimorphism. Males of diving beetles sometimes resort to coercive tactics to increase their chances of successful reproduction, which can impose costs on females. Sexual conflict can also drive sexual size dimorphism (SSD), particularly in species where males are larger than females. In this context, Rensch's rule states that SSD tends to increase with body size in species with male-biased SSD and decrease with body size in species with female-biased SSD. The role of sexual conflict in driving the evolution of the allometric relationships between males and females remains unclear. We addressed whether sexual conflict in diving beetles might drive SSD. We found that dytiscids do not follow Rensch's rule, whereby the SSD is isometric in relationship to species body size. Species with adhesive pads (Dytiscinae) showed a more pronounced SSD than other diving beetle species. These results suggest that the presence of adhesive pads might reduce the force necessary to control female movement during copulation and drive the evolution of smaller males. The findings of this study provide new insights into the role of sexual conflict in driving the evolution of SSD in animals. [ABSTRACT FROM AUTHOR]

Animals communicate acoustically to report location, identity, and emotive state to conspecifics. Acoustic signals can also function as displays to potential mates and as territorial advertisement. Music and song are terms often reserved only for humans and birds, but elements of both forms of acoustic display are also found in non‐human primates. While culture, bonding, and side‐effects all factor into the emergence of musicality, biophysical insights into what might be signaled by specific acoustic features are less well understood. Objectives: Here we probe the origins of musicality by evaluating the links between musical features (structural complexity, rhythm, interval, and tone) and a variety of potential ecological drivers of its evolution across primate species. Alongside other hypothesized causes (e.g. territoriality, sexual selection), we evaluated the hypothesis that perilous arboreal locomotion might favor musical calling in primates as a signal of capacities underlying spatio‐temporal precision in motor tasks. Materials and Methods: We used musical features found in spectrographs of vocalizations of 58 primate species and corresponding measures of locomotion, diet, ranging, and mating. Leveraging phylogenetic information helped us impute missing data and control for relatedness of species while selecting among candidate multivariate regression models. Results: Results indicated that rapid inter‐substrate arboreal locomotion is highly correlated with several metrics of music‐like signaling. Diet, alongside mate‐choice and range size, emerged as factors that also correlated with complex calling patterns. Discussion: These results support the hypothesis that musical calling may function as a signal, to neighbors or potential mates, of accuracy in landing on relatively narrow targets. [ABSTRACT FROM AUTHOR]

Morphological variation of body size and appendages is defined as polymorphism and may be associated with important structures linked to the sexual selection process. Some studies have suggested an expressive heterochely (i.e., dissimilar chelipeds) in the male adult phase of the semi-terrestrial crab Ucides cordatus , an important decapod species of mangrove systems from the western Atlantic. Here, the morphology, size, and growth pattern of male chelipeds in U. cordatus from the Brazilian coast were examined to test for polymorphism, considering that adult males usually develop one ornamented and hypertrophied cheliped. Two cheliped morphs were detected in U. cordatus males: chelipeds can be either homochelous or heterochelous and both morphotypes occur from the juvenile to adult phase. The higher frequencies of heterochelous males in larger size classes (71%: ⩾51 mm CW) and homochelous males in smaller ones (56%: <51 mm CW) confirmed that the prevalence of each morph is also associated with the ontogeny in males. The ornamentation of both morphs mainly differed in the dentition of cutting edges, but it was similar in the presence and position of tubercles. Adult crabs with homochelous and heterochelous chelipeds reached a similar body size, but their major chelipeds were significantly different in size and growth pattern. The presence of both cheliped morphs suggests the existence of distinct functions in this species, associated with feeding habits and behavioral displays (sexual / agonistic interactions). Our results indicate that more than one morph can participate in the reproductive process in species with mating systems (e.g., explosive breeding) allowing for this, as in the subfamily Ucidinae. [ABSTRACT FROM AUTHOR]

Female sperm storage organs in arthropods are used as taxonomic characters since it is assumed that they do not change after maturation. However, in the Golden Silk spider, Trichonephila clavipes, the shape and sclerotization of the spermathecae change with a mating event. Moreover, mating in T. clavipes consists of several hundred copulations, but the male transfers all sperm during the first insertion of each pedipalp. Given this puzzling mating behaviour, we hypothesize that multiple copulations serve purposes other than sperm transfer and uptake, such as further altering the morphology of the storage site and/or transferring substances other than sperm. We compared virgin female T. clavipes with females after two copulations, one for each spermatheca, and after ad‐libitum mating. Each treatment consisted of two sub‐treatments in which the state of the sperm storage organs was inspected after a short (1–3 days) or a long (11 days) time interval after the female's final moult. The size of the spermathecae increased twofold in all mating treatments compared to virgin females. The thickness of the spermathecal wall increased significantly with time in all treatments similarly. The spermathecal epithelium, which releases secretion into the lumen of the spermathecae, seems most active in virgin females during the time when mating would normally occur and turns less active after mating and with age. The spermathecae contain secretion produced by the female before mating; and after mating, sperm and another secretion transferred by the male. The numerous sperm‐less matings in the ad‐libitum treatment resulted in male secretion in the copulatory ducts of the female genitalia, likely impeding sperm transfer by subsequent males. Out study shows that female genitalia can change considerably after having reached maturity and suggests that sperm‐less matings evolved in the context of sperm competition. [ABSTRACT FROM AUTHOR]

The bewildering courtship phenotypes of male birds of paradise (Paradisaedae) represent a classic example of sexual selection through mate choice. While the majority of sexual selection studies have focused on either mate choice or intrasexual competition, males across a variety of taxa adopt alternative mating tactics as additional means of obtaining fertilization when they are otherwise unable to. For example, across various polygynous birds, subordinate males engage in sneak copulations, which may offset the fitness costs of prolonged subordinate periods. Despite exhibiting strong mating skews and male delayed plumage maturation, reports of sneak copulation in the birds of paradise are exceedingly rare. After reviewing an extensive video collection of courtship interactions, we found examples of mountings by female‐plumaged birds in three birds of paradise species: the Western parotia Parotia sefilata, Carola's parotia Parotia carolae, and the magnificent bird of paradise Cicinnurus magnificus. While homosexual mountings by females have been documented previously in Lawes' parotia P. lawesii, adult males in the magnificent bird of paradise violently attacked intruding female‐plumaged birds attempting to mount receivers, suggesting that they may be immature males engaging in alternative mating tactics. Overall, the rare video footage described here is suggestive of two fascinating, yet unexplored phenomena in polygynous birds: alternative mating tactics and female homosexual behaviour. [ABSTRACT FROM AUTHOR]

The maintenance of polymorphisms often depends on multiple selective forces, but less is known on the role of stochastic or historical processes in maintaining variation. The common wall lizard (Podarcis muralis) is a colour polymorphic species in which local colour morph frequencies are thought to be modulated by natural and sexual selection. Here, we used genome‐wide single‐nucleotide polymorphism data to investigate the relationships between morph composition and population biogeography at a regional scale, by comparing morph composition with patterns of genetic variation of 54 populations sampled across the Pyrenees. We found that genetic divergence was explained by geographic distance but not by environmental features. Differences in morph composition were associated with genetic and environmental differentiation, as well as differences in sex ratio. Thus, variation in colour morph frequencies could have arisen via historical events and/or differences in the permeability to gene flow, possibly shaped by the complex topography and environment. In agreement with this hypothesis, colour morph diversity was positively correlated with genetic diversity and rates of gene flow and inversely correlated with the likelihood of the occurrence of bottlenecks. Concurrently, we did not find conclusive evidence for selection in the two colour loci. As an illustration of these effects, we observed that populations with higher proportions of the rarer yellow and yellow‐orange morphs had higher genetic diversity. Our results suggest that processes involving a decay in overall genetic diversity, such as reduced gene flow and/or bottleneck events have an important role in shaping population‐specific morph composition via non‐selective processes. [ABSTRACT FROM AUTHOR]

Identifying the evolutionary drivers of sexual signal complexity is a key challenge in the study of animal communication. Among mammals, male bovids and cervids often perform elaborate gestural displays during courtship, consisting of ritualized movements of various parts of the body but the causes underlying interspecific variation in complexity of such displays remain poorly understood. Here we apply the comparative method to investigate which factors may have either promoted or constrained gestural repertoire size. We found that sexual selection was a strong predictor of gestural display complexity in male bovids and cervids. Repertoire size was positively correlated with breeding group size, an indicator of the intensity of sexual selection in males. Moreover, repertoires were larger in species adopting nonterritorial and lek breeding mating systems than in species adopting resource-defence territoriality, a finding that can be explained by more emphasis on direct benefits than indirect benefits in resource-defence systems, where male mating success may also be less skewed due to difficulty in monopolizing mates. The results also indicate that gestural repertoire size was positively correlated with the number of closely related species occurring in sympatry. This is consistent with display complexity being selected to facilitate species recognition during courtship and thereby avoid interspecific hybridization. At the same time, repertoire size was negatively associated with male body mass, possibly due to the energetic and mechanical constraints imposed on movements in very large species. By contrast, we found no evidence that the habitat drives selection for complex gestural courtship displays. [ABSTRACT FROM AUTHOR]

Ever since Darwin's pioneering work, the definition of sexual selection has been subject to recurrent controversies. The main focus of a more recent debate centers on whether or not sexual selection encompasses intra-sexual competition for resources other than gametes. Specifically, it has been proposed to define sexual selection as competition for access to gametes and to consider competition for any other resources provided by mates as forms of natural selection. In this review, I elaborate on several drawbacks of this gamete-centered approach arguing that it (1) implies an artificial split of pre-copulatory competition for mates into two indistinguishable processes, (2) hinders the identification and quantification of sexual selection and, therefore, its distinction from other forms of natural selection, (3) gives rise to an overly male-biased perception on sexual selection, and (4) does not conform to Darwin's original conception. In an attempt to provide a definition, which is explicit regarding the ultimate target of intra-sexual competition, I propose to define sexual selection as competition for access to reproductive resources provided by potential mating partners. I specify the main characteristics of this alternative definition in the context of previous ones and discuss potential limitations. [ABSTRACT FROM AUTHOR]

Sexual dimorphism can evolve in response to sex-specific selection pressures that vary across habitats. We studied sexual differences in subterranean amphipods Niphargus living in shallow subterranean habitats (close to the surface), cave streams (intermediate), and cave lakes (deepest and most isolated). These three habitats differ because at greater depths there is lower food availability, reduced predation, and weaker seasonality. Additionally, species near the surface have a near-even adult sex ratio (ASR), whereas species from cave lakes have a female-biased ASR. We hypothesized (a) a decrease in sexual dimorphism from shallow subterranean habitats to cave lake species because of weaker sexual selection derived from changes in the ASR and (b) an increase in female body size in cave lakes because of stronger fecundity selection on account of oligotrophy, reduced predation, and weaker seasonality. We measured body size and two sexually dimorphic abdominal appendages for all 31 species and several behaviours related to male competition (activity, risk-taking, exploration) for 12 species. Species with an equal ASR that live close to the surface exhibited sexual dimorphism in all three morphological traits, but not in behaviour. The body size of females increased from the surface to cave lakes, but no such trend was observed in males. In cave lake species, males and females differed neither morphologically nor behaviourally. Our results are consistent with the possibility that sexual and fecundity selection covary across the three habitats, which indirectly and directly, respectively, shape the degree of sexual dimorphism in Niphargus species. [ABSTRACT FROM AUTHOR]

Understanding how the early stages of sexual signal diversification proceed is critically important because these microevolutionary dynamics directly shape species trajectories and impact macroevolutionary patterns. Unfortunately, studying this is challenging because signals involve complex interactions between behavior, morphology, and physiology, much of which can only be measured in real-time. In Hawaii, male Pacific field cricket song attracts both females and a deadly parasitoid fly. Over the past two decades, there has been a marked increase in signal variation in Hawaiian populations of these crickets, including novel male morphs with distinct mating songs. We capitalize on this rare opportunity to track changes in morph composition over time in a population with three novel morphs, investigating how mate and parasitoid attraction (components of sexual and natural selection) may shape signal evolution. We find dramatic fluctuation in morph proportions over the three years of the study, including the arrival and rapid increase of one novel morph. Natural and sexual selection pressures act differently among morphs, with some more attractive to mates and others more protected from parasitism. Collectively, our results suggest that differential protection from parasitism among morphs, rather than mate attraction, aligns with recent patterns of phenotypic change in the wild. [ABSTRACT FROM AUTHOR]

Understanding what processes shape the formation of species' geographic range limits is one central objective linking ecology and evolutionary biology. One potentially key process is sexual selection; yet, theory examining how sexual selection could shape eco-evolutionary dynamics in marginal populations is still lacking. In species with separate sexes, range limits could be shaped by limitations in encountering mates at low densities. Sexual selection could therefore modulate mate limitation and resulting extinction–colonization dynamics at range margins, through evolution of mate encounter ability and/or mate competition traits, and their demographic consequences. We use a spatially explicit eco-genetic model to reveal how different forms of sexual selection can variably affect emerging range limits. Larger ranges emerged when sexual selection acted exclusively on traits increasing mate encounter probability, thus reducing female's mate limitation toward the range margins. In contrast, sexual selection via mate competition narrowed range limits due to increased trait-dependent mortality in males and elevated mate limitation for females. When mate encounter coevolved with mate competition, their combined effects on range limits depended on the mating system (polygyny vs. monogamy). Our results demonstrate that evolution of species' ranges may be importantly shaped by feedbacks between sexual selection and spatial population demography and dynamics. [ABSTRACT FROM AUTHOR]

Seminal fluid protein (Sfp) genes show, in general, a higher rate of sequence divergence than genes from other categories, which is often attributed to forms of postcopulatory sexual selection or sexual conflict. Recently, the relaxation of selective constraints has been proposed as an alternative explanation for the rapid sequence evolution of Sfps and other genes with sex-limited expression. The expression of Sfp genes is a likely target of selection, but the evolution of differences in their expression levels is less understood. Here, we explore both polymorphism and divergence in Sfp gene expression between Drosophila melanogaster and Drosophila simulans , how selection might have influenced their expression, and whether changes in expression might trigger the evolution of reproductive isolating barriers. In our analysis, Sfp genes showed higher divergence, but not higher polymorphism, in expression than the average male reproductive glands gene. Sfp genes with reproductive-tissue-specific expression were enriched for both directional and stabilizing selection, while relaxed selection was the predominant mode of evolution among Sfp genes with any other nonreproductive tissue-specific or nontissue-specific expression. The knockdown of single genes known to affect intraspecific sperm competition, and with patterns of expression divergence and polymorphism suggestive of directional selection, was not enough to break down postmating reproductive isolation barriers between species. Our results identify the expression of male-specific Sfp genes as an enriched target of selection and suggest a complex molecular relationship between postcopulatory sexual selection on a single gene's expression and its effect on the onset of speciation. [ABSTRACT FROM AUTHOR]

Understanding variation in trait allometry and the drivers of variation in sexually selected traits is a major theme in evolutionary biology. The static allometries of sexually selected traits are often positive due to disproportional investment by large individuals into trait size. Comparative studies of weapon allometry are rare, and typically focus on variation along a single dimension (e.g. length), despite weapons often diverging dramatically in shape. Furthermore, studies predominantly focus on groups where weapons have evolved as novel structures (e.g. horns), despite most weapons arising from modifications of existing structures.We test the hypothesis that sexual selection drives variation in static allometry using a phylogenetic comparative approach with 59 brentine weevil species showing remarkable variation in trait exaggeration and sexual size dimorphism (SSD).Contrasting two dimensions of head size exaggeration (a sexually selected trait) and elytron length (a nonsexual trait), positive static allometry was common across both measures of male head size, but not females, and there was positive covariance between male head static allometry and SSD across species. Positive static allometry for male elytron length was less common, but did show positive covariance with SSD, possibly due to the function of wings as compensatory structures for bearing large weapons.Our findings support the hypothesis that sexual selection drives the evolution of allometries both within and among species, and that the modification of existing structures to be used as weapons does not limit the potential for positive static allometry. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Female mate choice decisions are guided by preferences for male display features, but in chorusing species the displays of different males may temporally overlap. Here, mate choice decisions may be guided by preferences based on signal timing in addition to signal features. Which type of preference dominates has implications for our understanding of the dynamics of sexual selection in group-displaying animals. I presented female treefrogs with a series of playback treatments varying the amounts of calls in leader/follower position to establish the lowest proportion of leading calls resulting in a preference. About half the females expressed leader preferences when fewer than 15% of calls are in leading position (the maximum produced by chorusing males). This suggests that mate choice decisions will be dominated by call timing preferences in some females, and by call features preferences others, overall lowering the strength of selection on either male display trait. [ABSTRACT FROM AUTHOR]

Social interactions (e.g. aggression, mating and parenting) often depend on the social environment, and recent studies suggest that the adult sex ratio (ASR, the proportion of males in the adult population) modulates these social interactions. While observational studies and phylogenetic analyses provide strong support for the proposition that the relative frequencies of adult males and females impact social decisions, the experimental evidence for the impacts of ASR on social interactions is moot. In this study, we manipulated ASR in dung beetles, Onthophagus taurus , to test the responses of males and females in contest behaviour, courtship behaviour and breeding success. We found that ASR influenced the intensity of both contest and courtship, with both contests and courtships being more frequent in male-biased ASRs than in female-biased and unbiased treatments. The weight of brood balls did not differ significantly between ASR treatments, suggesting that ASR does not affect the breeding success of dung beetles by changing the parental investment of females and males. Moreover, the mean number of brood balls per male was fewer in male-biased treatments than in female-biased and unbiased treatments, while there was no significant difference in the mean number of brood balls per female between treatments, supporting the hypothesis that a male-skewed ASR can impair the breeding success of organisms by influencing the reproductive capacity of males but not females. Our results extend the understanding of the influence of ASR on the reproductive strategy decisions of males and females in breeding success. Future analyses are needed to understand the physiological and genetic implications of mate choice and contest behaviour in the context of a variable social environment, as represented by ASR. • An increased male-biased ASR frequently intensifies contest and courtship behaviour. • ASR shows no impact on parental care, evidenced by consistent brood ball weights. • ASR shifts male, not female, reproductive capacity, impacting breeding success. • There is no ASR effect on the parental care–fecundity trade-off in our experiment. [ABSTRACT FROM AUTHOR]

Empirical and theoretical evidence suggests that getting injured during combat decreases an individual's chances of winning. Thus, it has been hypothesized that species that engage in injurious fights may evolve armour. However, much remains unknown about the role that male–male combat has in promoting the evolution of such damage-reducing structures. Here, we tested the hypothesis that male–male combat can increase the damage resistance of structures using the giant mesquite bug, Pachylis neocalifornicus. When males in this species fight over access to mates, they use their weaponized hindlegs to puncture the dorsal side, but not the ventral side, of their rivals. We found that structures on the dorsal side of males could generally withstand the forces of combat, while structures on the dorsal side of females could not. The sexual dimorphism in damage resistance was location dependent because structures on the ventral side of both males and females also could not withstand the forces of combat. Thus, males appear to only increase their defensive capacity in the locations where strikes from rivals normally land. These results provide evidence that male–male combat can promote the evolution of damage-reducing structures (i.e. sexually selected shields). Moreover, the relatively inconspicuous nature of the sexually selected shields in this species suggests that defensive traits related to combat may be more common than currently considered. • We tested damage resistance of structures in the fighting insect P. neocalifornicus. • Male cuticle was harder to puncture than female cuticle. • Sexual dimorphism in damage resistance was location dependent. • Male armour can withstand some, but not all, fighting-related forces. [ABSTRACT FROM AUTHOR]