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Anisogamy, different-sized male and female gametes, sits at the heart of sexual selection and conflict between the sexes. Sperm producers (males) and egg producers (females) of the same species generally share most, if not all, of the same genome, but selection frequently favours different trait values in each sex for traits common to both. The extent to which this conflict might be resolved, and the potential mechanisms by which this can occur, have been widely debated. Here, we summarize recent findings and emphasize that once the sexes evolve, sexual selection is ongoing, and therefore new conflict is always possible. In addition, sexual conflict is largely a multivariate problem, involving trait combinations underpinned by networks of interconnected genes. Although these complexities can hinder conflict resolution, they also provide multiple possible routes to decouple male and female phenotypes and permit sex-specific evolution. Finally, we highlight difficulty in the study of sexual conflict over shared traits and promising directions for future research.

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.

Across internally fertilising species, males transfer ejaculate proteins that trigger wide-ranging changes in female behaviour and physiology. Much theory has been developed to explore the drivers of ejaculate protein evolution. The accelerating availability of high-quality genomes now allows us to test how these proteins are evolving at fine taxonomic scales. Here, we use genomes from 264 species to chart the evolutionary history of Sex Peptide (SP), a potent regulator of female post-mating responses in Drosophila melanogaster. We infer that SP first evolved in the Drosophilinae subfamily and has since followed markedly different evolutionary trajectories in different lineages. Outside of the Sophophora-Lordiphosa, SP exists largely as a single-copy gene with independent losses in several lineages. Within the Sophophora-Lordiphosa, the SP gene family has repeatedly and independently expanded. Up to seven copies, collectively displaying extensive sequence variation, are present in some species. Despite these changes, SP expression remains restricted to the male reproductive tract. Alongside, we document considerable interspecific variation in the presence and morphology of seminal microcarriers that, despite the critical role SP plays in microcarrier assembly in D. melanogaster, appears to be independent of changes in the presence/absence or sequence of SP. We end by providing evidence that SP's evolution is decoupled from that of its receptor, Sex Peptide Receptor, in which we detect no evidence of correlated diversifying selection. Collectively, our work describes the divergent evolutionary trajectories that a novel gene has taken following its origin and finds a surprisingly weak coevolutionary signal between a supposedly sexually antagonistic protein and its receptor.

Sexual selection can result in extreme development of multimodal mate-attracting traits, including complex constructions. Male Great Bowerbirds build bowers for attracting females. Bowers contain a thatched twig tunnel (avenue) opening onto 2 courts covered with decorations. Males displaying on a court are seen by a female from within the avenue. She sees and hears displays through the avenue entrance but can only see the males head and objects in his bill as it passes repeatedly across the entrance. Because the bower may affect the auditory as well as the visual parts of the multimodal male display we investigated bower acoustic properties by playing standard sounds from multiple court positions, recording the resulting sounds at the females head position within the avenue. Bower geometry results in a limited zone at the avenue entrance where his vocalisations can be heard with maximum intensity; this corresponds to his typical display position. Experiments show that court decorations increase the intensity of some frequencies and reduce the intensity of others. Bower structure simultaneously affects both visual and auditory male display components and could be important in sexual selection. It is important to consider more than 1 sensory mode, especially in the context of built signaling structures.

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.

Rich materials can provide more opportunities for exploring the mechanisms of speciation driven by sexual selection. Being the fastest‐evolving arthropods to date, the sword‐tailed crickets of Nudilla Gorochov, 1988 (= Laupala Otte, 1994) have rapidly diverged primarily due to the variability of their calling songs (sexual signals). In addition, they also exhibit morphological conservatism, with little variation between species. Similar circumstances can be seen in tree crickets (Oecanthinae), which have conservative morphology and a diverse range of song variations. Thus, we believe that tree crickets could serve as a model for research on sexual selection since they share a similar evolutionary history and mode of differentiation with Nudilla. However, due to the improper methods in analyzing the calling songs and nearly identical morphological features between taxa, there are many problems with the taxonomy of Oecanthinae in China. To solve these problems, we conducted an integrative taxonomic study of Chinese Oecanthinae based on comparative morphology, species delimitation, acoustical analysis, and phylogenetic analysis. This study recognized 12 Oecanthinae species in China, including four new species, and confirmed one new synonym and two misidentifications. Meanwhile, we confirmed the morphological stability of Oecanthinae, and revealed that variation in color, size, and morphology may be intraspecific polymorphism, which sometimes does not reflect the species relationships. The result indicates that the acoustic parameter freq.median can be used for efficient and accurate species delimitation in Oecanthinae. We speculate that incomplete species divergence leads to complexity in species relationships at the genetic level of Oecanthinae. The conservation of morphological characters, the interspecificity of songs and the complexity of species relationships suggest that sexual selection have played a role in the evolution of Oecanthinae. Our study resolves some systematic and taxonomic problems of Oecanthinae, clarifies the species relationships of Oecanthinae in China, and provides clues for expanding the cricket groups to be used in speciation studies. [ABSTRACT FROM AUTHOR]

ABSTRACT Intraspecific sexual communication, crucial in reproductive interactions, often involves the interchange of signals like vibrations, visual signals, and chemical compounds like sex chemical cues. Within the arachnids, solifuges (“camel spiders”) are an understudied group in terms of the detection of chemical compounds during mate searching and sexual interactions. In solifugids, the malleoli, chemoreceptor structures located on the ventral side of legs IV, are putative structures capable of capturing chemical signals. Our study focused on chemical male perception of female cues in Titanopuga salinarum (Ammotrechidae), examining associated behavioral modifications and the role of malleoli. We analyzed alterations in the motion pattern (activity pulse) and specific behaviors performed by males in association with female chemical stimuli. Using experimental arenas, we exposed males to female chemical cues stimuli similar to those available at the field. Stimuli comprised females (F) and cuticular extracts (CE), with corresponding controls. Males with intact malleoli (N = 26 with F, N = 20 with CE) were compared to those with malleoli removed (N = 21 with F, N = 17 with CE). We found partial evidence that males detect chemical cues of females deposited on the substrate. We observed no differences in the duration and number of the activity pulses spent in the zones with and without stimuli in any of the groups analyzed. However, the males exhibit significant changes in locomotion patterns in response to female chemical cues, suggesting a behavioral response to these stimuli. This finding suggests that the males of this species detect the female chemical cues and modify their behavior, and can quickly gather the necessary olfactory information where the stimulus is located. In addition, we found a possible condition‐dependent regime for the detection of female cues by males, which would be expected from life‐history characteristics of T. salinarum. Our findings prompt discussion from a sexual selection perspective, suggesting the importance of chemical communication in intraspecific interactions in this elusive but fascinating animal model. [ABSTRACT FROM AUTHOR]

ABSTRACT In most fishes, the number of offspring increases with maternal body size. Although this size‐fecundity relationship often varies among species as a result of the coevolution of life‐history traits, the genetic basis of such size‐fecundity relationships remains unclear. We explored the genetic basis underlying this size‐fecundity relationship in two small medaka species, Oryzias latipes and O. sakaizumii. Our findings showed that O. sakaizumii has a higher fecundity than O. latipes, and quantitative trait locus analysis using interspecific F2 hybrids showed that chromosome 23 is linked to the size‐fecundity relationship. In particular, the genes igf1 and lep‐b in this region are known to be associated with life‐history traits, including somatic growth, gonad maturation, and progeny numbers in various taxa. Because O. sakaizumii is distributed at higher latitudes and has a shorter spawning season than O. latipes in the wild, we propose that the relatively high fecundity observed in O. sakaizumii is an adaptation to high latitudes. We also discuss the potential ecological ramifications associated with the evolution of increased fecundity in this species. [ABSTRACT FROM AUTHOR]

ABSTRACT Long matings are abundant in insects despite the range of the costs involved. The causes and consequences of the evolution of long mating remain an interesting problem for behavioural ecologists. We studied extraordinarily long mating that involves repeated intromissions interspersed with latent periods in the Parthenium beetle (Zygogramma bicolorata). We conducted a series of interrupted mating assays to examine the fitness consequences of different components of this curious mating behaviour. We tested multiple adaptive hypotheses concerning male fertility and competitive ability. We found that sperm transfer and fertility did not exhibit a linear increase with the number of intromissions. There was also no evidence of nutrient transfer by the males. Interestingly, our results showed that both sexes suffered a significant cost of long mating. Further, female remating behaviour was found to be modulated by the length of the previous mating. Additionally, males were observed performing a curious leg rubbing behaviour during the inter‐intromission latent period, putatively serving as a copulatory courtship function that reduced female resistance to the continuance of mating. Therefore, we show that while the long mating may still serve a mate‐guarding role, there are additional fitness effects of such behaviour that need careful consideration. Our study provides insights into the adaptive significance of long mating and its fitness consequences. [ABSTRACT FROM AUTHOR]

Sexual selection, one of the central pillars of evolutionary theory, has powerful effects on organismal morphology, behaviour, and population dynamics. However, current knowledge about geographical variation in this evolutionary mechanism and its underlying drivers remains highly incomplete, in part because standardised data on the strength of sexual selection is sparse even for well-studied organisms. Here, we use information on mating systems—including the incidence of polygamy and extra-pair paternity—to estimate the intensity of sexual selection in 10,671 (>99.9%) bird species distributed worldwide. We show that avian sexual selection varies latitudinally, peaking at higher latitudes, although the gradient is reversed in the world's most sexually selected birds—specialist frugivores—which are strongly associated with tropical forests. Phylogenetic models further reveal that the strength of sexual selection is explained by temperature seasonality coupled with a suite of climate-associated factors, including migration, diet, and territoriality. Overall, these analyses suggest that climatic conditions leading to short, intense breeding seasons, or highly abundant and patchy food resources, increase the potential for polygamy in birds, driving latitudinal gradients in sexual selection. Our findings help to resolve longstanding debates about spatial variation in evolutionary mechanisms linked to reproductive biology and also provide a comprehensive species-level data set for further studies of selection and phenotypic evolution in the context of global climatic change. Sexual selection has powerful effects on organismal morphology, behavior and population dynamics, but how does it vary geographically, and what are the underlying drivers? This study of 10,671 bird species distributed worldwide reveals that avian sexual selection varies latitudinally, and is explained by temperature seasonality coupled with a suite of climate-associated factors. [ABSTRACT FROM AUTHOR]

Many animals communicate using multiple sensory modes (e.g., vibratory, visual, chemical), and there is current interest in the role of multimodal signals in mate choice. We tested the hypotheses that male Gladicosa bellamyi wolf spiders (Lycosidae) court females using multimodal signals and that these signals were related to male mating success. Using a laser Doppler vibrometer and video camera, we characterized the vibratory and visual courtship signals of male G. bellamyi. Males courted females with a vibratory signal made of three components: pulses of stridulation, abdominal percussion, and a third unknown percussive element (presumed to arise from rapid abdomen tapping), along with two unique visual displays, a foreleg extension/tap and squared leg arch. Female G. bellamyi show no apparent vibratory signals, but possess visual receptivity displays comparable to some other female lycosid species. We found a strong correlation between the vibratory stridulation component and the visual foreleg extension/tapping display of males, suggesting a multimodal signal. Higher rates of courtship signaling, both visual and vibratory, were associated with increased copulatory success. We conclude that male G. bellamyi exhibits multimodal courtship communication, with simultaneous complex vibratory signals and visual displays, and that higher rates of these signals increase the probability of mating in this species. [ABSTRACT FROM AUTHOR]

Mating signals are targets of conspecific signal recognition and sexual selection but are also subject to abiotic temperature effects and to biotic interspecific eavesdroppers. In crickets, the male calling song becomes faster at warmer temperatures, and female crickets' recognition of male song tracks temperature in a coordinated manner, termed "temperature coupling." But, female crickets are not the only ecologically relevant listeners: some cricket species are parasitized by Ormia ochracea , a parasitoid fly which finds its cricket hosts by eavesdropping on male cricket song. How temperature affects parasitoid fly phonotaxis to song is largely unexplored, with only one previous study conducted under field conditions. Here, we explore 6 possible patterns of thermal effects on fly responses to cricket song, including temperature coupling, using field playbacks of synthetic Gryllus lineaticeps songs designed to be species-typical at various temperatures. We find that temperature does affect fly response, but that the temperature deviation of songs from ambient does not impact numbers of flies caught. We extend this finding by comparing the temperatures of the air (where flies search for their hosts) and the ground (where their host crickets signal) to show that temperature coupling is unlikely to be effective given microhabitat variation and differential rates of cooling in the evening hours when flies are most active. Our results can be interpreted more broadly to suggest (1) temperature effects on intraspecific communication systems may be more tightly coupled than are effects on interspecific eavesdropping and (2) variation in thermal microhabitats in the field make it difficult to translate laboratory physiological responses to natural selection in the wild. [ABSTRACT FROM AUTHOR]

Evolutionary theory predicts that assortative mating is crucial for sympatric speciation by generating reproductive isolation between diverging populations. Here, we investigate the potential of form-assortative mating, an assumed mating pattern in lampreys, for sympatric speciation. By continuously recording mating activity between anadromous and freshwater-resident forms of L. camtschaticum that greatly differ in body size, we show that lampreys tend to mate with individuals of similar size in experimental conditions. However, we highlight that this pattern does not result from a choice of same-form partner but is the result of the simultaneous action of a preference of males—whatever their size—for large anadromous females, a higher competitive ability of aggressive males and physical constraints on heteroform pairs. Moreover, we do not advocate that sympatric speciation, as the sole consequence of form-assortative mating through sexual selection, is a plausible mechanism for the diversification of lampreys as a significant number of sneaking behaviors were observed in freshwater-resident males toward large anadromous females. Broader attention should be given to mechanisms other than the sexual selection that may lead to form-assortative mating, such as variations in the spatial or temporal distribution of alternative forms during reproductive season. [ABSTRACT FROM AUTHOR]

Competition for mates can drive the evolution of exaggerated weaponry and male dimorphism associated with alternative reproductive tactics. In terrestrial arthropods, male dimorphism is often detected as non-linear allometries, where the scaling relationship between weapon size and body size differs in intercept and/or slope between morphs. Understanding the patterns of non-linear allometries is important as it can provide insights into threshold evolution and the strength of selection experienced by each morph. Numerous studies in male-dimorphic arthropods have reported that allometric slopes of weapons are shallower in large "major" males compared to small "minor" males. Because this pattern is common among beetles that undergo complete metamorphosis (holometabolous), researchers have hypothesized that the slope change reflects resource depletion during pupal development. However, no comprehensive survey has examined the generality of this trend. We systematically searched the literature for reports of weapon allometries in male dimorphic species and conducted a phylogenetically controlled meta-analysis to explore the factors influencing the difference in slopes between morphs. Our search identified 59 effect sizes from 19 studies, 50 species, and 5 orders of terrestrial arthropods. We found strong evidence that metamorphosis type influences the patterns of weapon allometries. Slopes were significantly steeper in minor males compared to major males in holometabolous species, but there was no difference in slopes between morphs in hemimetabolous species (i.e. those that undergo incomplete or no metamorphosis). These results support the hypothesis that holometabolous species face a resource ceiling during pupal development that limits the exaggeration of weapon size. [ABSTRACT FROM AUTHOR]

The evolution of sexual ornaments in animals is typically attributed to reproductive competition. However, sexual ornaments also arise in contexts where the ornamented sex is neither mate nor gamete limited, and explanations for ornamentation in these cases remain incomplete. In many species, particularly those with slow life histories, lifetime reproductive success depends more strongly on adult survival than fecundity, and survival can depend on intersexual interactions. We develop a population genetic model to investigate how the effect of intersexual interactions on survival may contribute to ornament evolution in the absence of competition for mates. Using female ornamentation in polygynous mating systems as a case study, we show that, indeed, ornaments can evolve when the ornament functions to modify interactions with males in ways that enhance a female's own survival. The evolutionary dynamics depend qualitatively on the specific behavioral mechanism by which the ornament modifies social interactions. In all cases, the ornament's long-term persistence is ultimately determined by the coevolution of the male locus that determines how males affect female survival. We outline the scenarios that are most likely to favor the evolution of female ornaments through the effects of intersexual interactions on survival, and we urge empirical researchers to consider the potential for this social selection mechanism to shape traits of interest across taxa. [ABSTRACT FROM AUTHOR]

One of the most evident sources of phenotypic diversity within a population is colouration, as exemplified by colour polymorphism. This is relevant to a greater extent in animals with visually biased sensory systems. There is substantial evidence suggesting that different colour morphs can access a broader range of habitats or niches, leading to larger geographic range sizes. However, this hypothesis has been tested in few lineages, comprising species where colour is likely to be involved in sexual selection. Furthermore, some available evidence considers geographical variation as polymorphism, thus limiting our comprehension of how sympatric colour polymorphism can influence a species' geographic range. Through an extensive systematic literature review and a comparative analysis, we examined the relationship between colour polymorphism and range size or niche breadth in web-building spiders. We identified 140 colour polymorphic spider species, belonging mainly to the families Araneidae and Theridiidae. We found no evidence that colour polymorphic species differ significantly from non-polymorphic species in terms of range size and niche breadth, after accounting for phylogenetic relationships and other covariates. However, we did observe that colour polymorphic species were more likely to be found on islands compared to non-polymorphic species. Overall, our results indicate that the association between colour polymorphism and geographic range size may not exist among web-building spiders, or be as pronounced as in other lineages. This suggests that the strength of the association between colour polymorphism and ecological success might depend on the ecological role that colouration plays in each clade. [ABSTRACT FROM AUTHOR]

Competition for mates can play a critical role in determining reproductive success, shaping phenotypic variation within populations, and influencing divergence. Yet, studies of the role of sexual selection in divergence and speciation have focused disproportionately on mate choice. Here, we synthesize the literature on how mate competition may contribute to speciation and integrate concepts from work on sexual selection within populations—mating systems, ecology, and mate choice. Using this synthesis, we generate testable predictions for how mate competition may contribute to divergence. Then, we identify the extent of existing support for these predictions in the literature with a systematic review of the consequences of mate competition for population divergence across a range of evolutionary, ecological, and geographic contexts. We broadly evaluate current evidence, identify gaps in available data and hypotheses that need testing, and outline promising directions for future work. A major finding is that mate competition may commonly facilitate further divergence after initial divergence has occurred, e.g. upon secondary contact and between allopatric populations. Importantly, current hypotheses for how mate competition contributes to divergence do not fully explain observed patterns. While results from many studies fit predictions of negative frequency-dependent selection, agonistic character displacement, and ecological selection, results from ~30% of studies did not fit existing conceptual models. This review identifies future research aims for scenarios in which mate competition is likely important but has been understudied, including how ecological context and interactions between mate choice and mate competition can facilitate or hinder divergence and speciation. [ABSTRACT FROM AUTHOR]

The mate choice behaviours of females can greatly affect patterns of reproductive success in males and influence the evolution of sexually selected male traits. Population-level estimates of display preferences may provide an accurate estimate of the strength and direction of selection by female choice if all females in the population show homogeneous preferences. However, population-level estimates may yield misleading estimates if there is within-population variation in mate preferences. While it is increasingly clear that the latter situation is common in nature, empirical data on the magnitude of variation in female preferences are required to improve our current understanding of its potential evolutionary consequences. We explored variations in female preference functions for 3 male call properties in a treefrog. We document substantial within-population variation not only in peak preferences but also in preference function shape (open, closed, flat), with at best 62% of females sharing a preference function shape with the respective population curve. Our findings suggest that population curves may accurately capture the direction of sexual selection, but depending on the properties of the constituting individual functions they may over- or underestimate the strength of selection. Particularly population estimates suggesting weak selection may in fact hide the presence of individual females with strong but opposing preferences. Moreover, due to the high within-population variation in both peak preferences and preference function shapes, the population functions drastically underestimate the predicted variation in male mating success in the population. [ABSTRACT FROM AUTHOR]

In populations with separate sexes, genetic load due to deleterious mutations may be expressed differently in males and females. Evidence from insect models suggests that selection against mutations is stronger in males. This pattern will reduce deleterious allele frequencies at the expense of males, such that female mean fitness is greater than expected, preserving population persistence in the face of high mutation rates. While previous studies focus on reproductive success, mutation load depends on total selection in each sex, including selection for viability. We might expect minimal sex differences in viability effects in fruit flies, since male and female larvae behave similarly, yet many genes show sex-biased expression in larvae. We measured the sex-specific viability effects of nine "marker" mutations and 123 mutagenized chromosomes. We find that both types of mutations generally reduce viability in both sexes. Among marker mutations we detect instances of sex-biased effects in each direction; mutagenized chromosomes show little sex-specific mutational variance, but recessive lethals show a female bias, including in FlyBase records. We conclude that mutations regularly affect viability in a sex-specific manner, but that the strong pattern of male-biased mutational effects observed previously for reproductive success is not apparent at the pre-reproductive stage. [ABSTRACT FROM AUTHOR]

Defined as the killing of a newborn individual by a conspecific, infanticide by males is widespread in mammals. Results from this paper used genetic analysis to confirm and characterize the first report of non-parental infanticide in giant armadillos. Genetic evidence demonstrates that the killer male is unrelated to the killed infant but is the father of the next offspring. This evidence supports the sexual selection hypothesis, in which infanticide is used to obtain increased access to breeding females. [ABSTRACT FROM AUTHOR]

Understanding the maintenance of genetic variation in reproductive strategies and polymorphisms in the wild requires a comprehensive examination of the complex interactions between genetic basis, behaviour and environmental factors.We tested the association between three colour genotypes and variation in female pheromone signalling and male antennal morphology in the wood tiger moth (Arctia plantaginis). These moths have genetically determined white (WW, Wy) and yellow (yy) hindwings that are linked to mating success and fitness, with heterozygotes (Wy) having an advantage. We hypothesized that attractiveness and reproductive success are correlated, with Wy females being more attractive than the other two genotypes which could contribute to maintaining the polymorphism.Female attractiveness was tested by baiting traps with females of the three colour genotypes both in low‐ (i.e. field set‐up) and in high‐population density (i.e. large enclosure set‐up). Male's ability to reach females was correlated to their own colour genotype and antennal morphology (length, area and lamellae count).Contrary to our prediction, morph‐related reproductive success and attractiveness were not correlated. Heavier Wy females attracted a lower proportion of males compared to WW and yy females. Specifically, an increase in weight corresponded to a decreased Wy but increased yy female attractiveness. yy females were generally more attractive than others likely due to earlier pheromone release. In males, lamellae count and genetic colour morph were linked to the male's ability to locate females. Furthermore, male traits affected their ability to reach females in a context‐specific way. Males with denser antennae (i.e. higher lamellae count) and white males reached the females faster than yellows in the enclosure, while yellow males located females faster than whites in the field.Our results indicate that higher yy female attractiveness was likely affected by the combined effect of early pheromone release, female weight and higher population density. Males' searching success was affected by morph‐specific behavioural strategies and local population density. Ultimately, the combined effect of genotype‐related pheromone signalling strategies of females together with environment‐dependent male behaviour affect male response and potentially contribute to maintaining variation in fitness‐related traits. [ABSTRACT FROM AUTHOR]

Environmental conditions (i.e., climatic variation) can strongly influence the cost and benefits of reproductive traits. Yet there is still no consensus on whether changing environmental conditions strengthen or relax sexual selection. Evidence from the literature suggests that highly variable environments can limit mate choice and investment in sexual traits, hence relaxing sexual selection pressures. Here, we tested this hypothesis using the nuptial gift-giving spider Paratrechalea ornata , in which males can either wrap nutritive (fresh prey) or worthless (prey leftovers) items in silk. We examined changes in males' sexual trait and female choice among six populations living under different climatic conditions. We found that large variation in precipitation limits female choice, potentially favoring the spread of deceptive worthless gifts. In populations under highly variable conditions and with the highest frequencies of worthless gifts (70%), males offering such gifts acquire longer mating durations than those offering nutritive gifts. In contrast, in populations with less variable conditions and the lowest frequencies of worthless gift (36%), females shortened mating duration to males offering worthless gifts. Our findings are consistent with the prediction that highly variable environmental conditions relax sexual selection. [ABSTRACT FROM AUTHOR]

Large structural variants in the genome, such as inversions, may play an important role in producing population structure and local adaptation to the environment through suppression of recombination. However, relatively few studies have linked inversions to phenotypic traits that are sexually selected and may play a role in reproductive isolation. Here, we found that geographic differences in the sexually selected plumage of a warbler, the common yellowthroat (Geothlypis trichas), are largely due to differences in the Z (sex) chromosome (males are ZZ), which contains at least one putative inversion spanning 40% (31/77 Mb) of its length. The inversions on the Z chromosome vary dramatically east and west of the Appalachian Mountains, which provides evidence of cryptic population structure within the range of the most widespread eastern subspecies (G. t. trichas). In an eastern (New York) and western (Wisconsin) population of this subspecies, female prefer different male ornaments; larger black facial masks are preferred in Wisconsin and larger yellow breasts are preferred in New York. The putative inversion also contains genes related to vision, which could influence mating preferences. Thus, structural variants on the Z chromosome are associated with geographic differences in male ornaments and female choice, which may provide a mechanism for maintaining different patterns of sexual selection in spite of gene flow between populations of the same subspecies. [ABSTRACT FROM AUTHOR]

During courtship, animals perform conspicuous and elaborate signals. In birds, courtship involved often mutual engagement by both partners but most research on courtship behaviours has focused on male signals despite of growing interest for female signals in recent years. Here, we show that female domestic canaries (Serinus canaria) have the ability to modulate their sexual response to male songs. To do so, we exposed females to two types of song (very attractive and moderately attractive songs) during two consecutive reproductive cycles. We measured both visual (copulation solicitation displays, CSD) and vocal signals (copulation solicitation trills, CST; contact calls, CC and simple trills, ST) emitted by the females during song broadcast. We observed that females could modify the characteristics of their signals (duration and the number of elements of CSD, duration, frequency and number of notes of calls) depending on song attractiveness and the number of times they were exposed to a male's song. We also found that some females always emitted more signals than others (i.e. stable inter‐individual differences) regardless of the song attractiveness and across reproductive cycles. Further studies are necessary to check whether female signals constitute sexual ornaments and if they could stimulate male canaries during courtship. [ABSTRACT FROM AUTHOR]

The optimal timing of sexual behaviours across a daily cycle can form a key component of mating and reproductive success. However, few studies have explored circadian rhythms in mating behaviour within the context of sexual selection and sexual conflict. Here we characterized circadian patterns in female receptivity to mating and the frequency of male mating and courtship behaviours in freely interacting captive groups of red junglefowl, Gallus gallus , in outdoor enclosures. We showed that patterns of male sexual behaviour and female resistance to mating attempts differ between the morning and evening during a 10-day mating trial. Females progressively reduced their level of resistance to male mating attempts during the early hours of the morning and progressively increased their resistance in the evening. Males did not match their mating frequencies to female receptivity and initiated mating attempts more often in the evening, but tended to perform more courtship displays in the morning. The pattern of male behaviour was associated with social status, such that dominant males courted females more often than subordinates, particularly in the morning. However, we did not find strong evidence that male social status was associated with different timing strategies. These results demonstrate circadian patterns in multiple sexual behaviours in red junglefowl, with potential consequences for sexual selection in this species and welfare management in domestic populations of closely related fowl. • Sexual selection may target individual variation in circadian behaviour. • Sex differences in the optimal timing of behaviours can drive sexual conflict. • We quantified circadian patterns in sexual behaviour in a polygynandrous bird. • Males courted more in the morning and female resistance was highest in the evening. • Male social status was not associated with different timing strategies. [ABSTRACT FROM AUTHOR]

Alternative reproductive tactics (ARTs) offer a unique window into how sexual selection can shape cognition and nonreproductive behaviour. Sexual selection more broadly has been shown to shape cognitive traits but has rarely been investigated in the context of ARTs. Furthermore, the divergent morphology and sexual behaviour associated with ARTs may lead to different socioecological challenges (e.g. predation, space use) that further shape nonreproductive behaviours. We take advantage of the behavioural diversity in alternative reproductive tactics among male El Abra swordtails, Xiphophorus nigrensis , to ask how cognition and behaviour diverge between male tactics. We tested courting (large), coercive (small) and mixed-strategy (intermediate-sized) male phenotypes in four assays to evaluate boldness, aggression, exploration, spatial learning and spatiotemporal learning. We found that the courting-only large male phenotype had faster latencies to the reward in the spatial learning assay than the other two male phenotypes and also had greater accuracy than chance. Furthermore, we found that courting phenotypes (large and intermediate-sized males) had greater increases in accuracy over successive trials than the coercive-only small male phenotype. We also found that small, coercive male phenotypes were bolder than large and intermediate-sized males. We found no differences in aggressive behaviour (directed at a mirror) or spatiotemporal learning (shuttle box assay) across the three phenotypes. We suggest that courting males' superior spatial learning abilities may reflect their defence of females at ephemeral foraging patches as well as their need for reliable escape routes from predators. Coercive males' increased boldness may bolster their persistent behaviour and reflect reduced predation pressure. These results suggest that sexual selection for alternative reproductive strategies affects nonreproductive behaviour and cognition in directions that may align with divergent socioecological challenges associated with each mating type. • We examine how cognition and behaviour diverge in male swordtail mating tactics. • Courtship was associated with greater performance in a spatial learning task. • Coercive-only phenotypes were more bold. • Mating tactic did not explain differences in spatiotemporal learning or aggression. [ABSTRACT FROM AUTHOR]

Scapula shape is highly variable across humans and appears to be sexually dimorphic—differing significantly between biological males and females. However, previous investigations of sexual dimorphism in scapula shape have not considered the effects of allometry (the relationship between size and shape). Disentangling allometry from sexual dimorphism is necessary because apparent sex‐based differences in shape could be due to inherent differences in body size. This study aimed to investigate sexual dimorphism in scapula shape and examine the role of allometry in sex‐based variation. We used three‐dimensional geometric morphometrics with Procrustes ANOVA to quantify scapula shape variation associated with sex and size in 125 scapulae. Scapula shape significantly differed between males and females, and males tended to have larger scapulae than females for the same body height. We found that males and females exhibited distinct allometric relationships, and sexually dimorphic shape changes did not align with male‐ or female‐specific allometry. A secondary test revealed that sexual dimorphism in scapula shape persisted between males and females of similar body heights. Overall, our findings indicate that there are sex‐based differences in scapula shape that cannot be attributed to size‐shape relationships. Our results shed light on the potential role of sexual selection in human shoulder evolution, present new hypotheses for biomechanical differences in shoulder function between sexes, and identify relevant traits for improving sex classification accuracy in forensic analyses. [ABSTRACT FROM AUTHOR]

Anuran advertisement calls can provide accurate information on the reproductive quality of the male callers, thus providing females with indicators for the selection of mates. Body size is generally correlated with the dominant frequency of male advertisement calls. However, it is unclear whether and to what extent call parameters are associated with gonadal investment and the energy reserves of the males. Given that in tropical seasonally dry environments the wet season is very short, gathering information about gonadal investment and energy reserves of mates should be particularly important. In the present study, we evaluated the relationship between acoustic performance, gonadal condition, and fat storage in the Neotropical frog Physalaemus albifrons from the Brazilian semiarid region, testing the hypothesis that the advertisement call (repetition rate, call duration, and fundamental and dominant frequencies) would be a good predictor of male quality in terms of gonadal investment (testicle length) and energy reserves (mass of fat bodies). Contrary to our predictions, neither testicle length nor the mass of fat bodies was related to any of the acoustic parameters of the advertisement calls of P. albifrons. These results indicate that the advertisement call of P. albifrons does not provide reliable information on gonadal investment or energy storage of males. Possibly, in habitats with little and unpredictable rainfall, males of P. albifrons should present small variation in gonadal and fat storage conditions during its short reproductive window. Our findings contribute to the understanding of anuran reproductive strategies in seasonally dry environments. [ABSTRACT FROM AUTHOR]

Common wall lizards (Podarcis muralis) in Italy show a striking variation in body coloration across the landscape, with highly exaggerated black and green colors in hot and dry climates and brown and white colors in cool and wet climates. Males are more intensely colored than females, and previous work has suggested that the maintenance of variation in coloration across the landscape reflects climatic effects on the strength of male–male competition, and through this sexual selection. However climatic effects on the intensity of male–male competition would need to be exceptionally strong to fully explain the geographic patterns of color variation. Thus, additional processes may contribute to the maintenance of color variation. Here we test the hypothesis that selection for green and black ornamentation in the context of male–male competition is opposed by selection against ornamentation because the genes involved in the regulation of coloration have pleiotropic effects on thermal physiology, such that ornamentation is selected against in cool climates. Field observations revealed no association between body coloration and microhabitat use or field active body temperatures. Consistent with these field data, lizards at the extreme ends of the phenotypic distribution for body coloration did not show any differences in critical minimum temperature, preferred body temperature, temperature‐dependent metabolic rate, or evaporative water loss when tested in the laboratory. Combined, these results provide no evidence that genes that underlie sexual ornamentation are selected against in cool climate because of pleiotropic effects on thermal biology. Research Highlights: Common wall lizards in Italy show a striking variation in coloration across the landscape with highly exaggerated coloration occurring in hot and dry climates.This could be because climate selects for coloration in warm climates and/or because the genes that underlie.We show that there are no differences in thermal traits between lizards with different color phenotypes providing limited evidence for the antagonistic pleiotropy hypothesis. [ABSTRACT FROM AUTHOR]

Many species exhibit alternative mating tactics (ARTs), with larger socially dominant males competing for females and smaller males adopting "sneaker" strategies to exploit fertilisation opportunities without competition or courtship. Females typically prefer larger socially dominant males, but their ability to manipulate mating or fertilisation outcomes is largely unknown. Here, using chinook salmon Oncorhynchus tshawytscha, we examined whether the female's ovarian fluid (OF) differentially influences the temporal patterns of sperm swimming traits in ejaculates from non-preferred sneaker ('parr') and preferred (dominant) males. Results demonstrate that OF improves sperm swimming speed and linearity compared to river water, regardless of male mating tactic. We report a novel tactic-specific difference in sperm linearity in which parr male sperm initially maintain straighter trajectories in river water, compared to dominant males, but then rapidly change to less linear and more circular paths over time. Intriguingly, we show that OF counteracts this change in sperm linearity in parr males so that patterns become indistinguishable from dominants when parr sperm swim in OF. Together, these results show that male chinook salmon exhibit differential sperm trait investment strategies depending on reproductive tactic. [ABSTRACT FROM AUTHOR]

Infanticide occurs in a diversity of taxa and may provide benefits to the perpetrator through nutritional gain, reduced competition, or increased fitness from mating opportunities through sexually selected infanticide (SSI). Infanticide, however, is rarely observed. We documented a probable infanticide event by a 23-year-old adult male polar bear (Ursus maritimus) on a 3-month-old cub in western Hudson Bay, Canada, during the spring of 2023. We subsequently documented a 21-year-old solitary female who was lactating and in breeding condition with swollen labia, suggesting polar bears return to estrous quickly in the absence of cubs. Using the literature, we examined the relationships among polar bear cub-of-the-year, adult male survival, and the ratio of male/female mortality. We suggest SSI as the plausible explanation for the infanticide event observed and discuss how indirect effects from climate change may affect the prevalence of infanticide as a mechanism regulating polar bear populations. [ABSTRACT FROM AUTHOR]

Although sexual selection can be a powerful evolutionary force in shaping the phenotype, sexually selected traits do not evolve in isolation of other traits or without influence from other selective pressures. Expensive tissues, such as brains, can constrain the evolution of sexually selected traits, such as testes, as can other energetically expensive processes, like the costs of locomotion. However, simple linear or binary analyses of specific traits of interest can prevent detection of important links within the integrated phenotype and obfuscate the importance of multiple selective forces. We used phylogenetically informed path analysis to determine causal links among mating system type, pace of life history, costs of locomotion, brain size, and testis size across 48 mammal species that exhibit a wide range of body sizes, life-history strategies, and types of locomotion. We found species with non-monogamous mating systems were associated with larger testes, faster life histories, and lower costs of locomotion compared to monogamous species. Having a larger brain was associated with a slower life history and, surprisingly, larger testes. In addition to highlighting the non-intuitive nature of certain causal relationships, our results also emphasize the utility of including multiple traits in studies of sexually selected traits, as well as considering the constraints imposed by linked traits and selection on those linked traits. [ABSTRACT FROM AUTHOR]

Producing and maintaining sexually selected ornaments often hinders survival. Because viability-related traits dictate the survival costs conferred by sexual ornaments, the evolution of viability-related traits can limit and/or compensate for ornament evolution. Here, we examine how the ornamental coloration of male dragonflies co-adapts with thermal physiology--a key suite of viability-related traits that influences nearly all reproductive and ecological interactions. Males of many dragonfly species produce dark color patches on their wings to attract potential mates and intimidate reproductive rivals. However, dark coloration also subjects male dragonflies to heat stress in warm climates by absorbing excess solar radiation. Our phylogenetic comparative analyses revealed that dragonfly species with dark sexual coloration have also evolved increased critical thermal maxima, which may allow them to compensate for ornament-induced heating. This pattern of correlated evolution was especially strong for species that inhabit tropical climates, where the heating costs of dark coloration are most severe. Given that darkened sexual coloration is taxonomically widespread and consistently elevates body temperatures, the pattern of co-adaptation between sexual ornaments and thermal physiology found here could represent a key process driving eco-physiological divergence in the past and influencing how populations respond to the changing climates of the future. [ABSTRACT FROM AUTHOR]

Male-male competition is a component of Darwin's theory of precopulatory intrasexual selection, where males compete for access to resources important for reproduction and successful males pass on traits that endow greater competitive ability to their offspring, thereby exaggerating the trait(s) over evolutionary time. Metals, such as lead (Pb) often occur in urban mangrove forests, where shore crabs reside, and being neurotoxic may cause sub-lethal effects on behaviour. In this study, we asked whether exposure to Pb influences the outcomes of male-male competition in the Semaphore crab, Heloecius cordiformis, thereby altering outcomes of intrasexual selection. Crabs were exposed to an environmentally relevant, and a behaviourally relevant, concentration of lead (i.e. Pb, 10 µg/L and 100 µg/L respectively) under laboratory conditions for 96 h and subsequently allowed to compete for burrow ownership in experimental arenas. Exposed crabs (100 µg/L) were less successful than control crabs in chela size-matched paired competitive interactions, spent less time in burrows and predominantly lost burrow ownership. Further, exposure to Pb contamination (both 10 µg/L and 100 µg/L) negated the chela size advantage in size-asymmetric competitive interactions. This contaminant-induced loss of size-related competitive advantage may result in relaxation in selection pressure on body size and smaller male carapace widths and especially male chela lengths in contaminated locations. Assessment of a range of locations in the wild found a consistent pattern of metal-associated size declines in more contaminated locations for males, but not for females. [ABSTRACT FROM AUTHOR]

ABSTRACT Species lacking distinct secondary sex characteristics, such as differences in size or morphology, are often thought to experience lower levels of sex‐specific selection in comparison to highly sexually dimorphic organisms. However, monomorphism in classic visible traits could be a result of genetic or physiological constraints that prevent the sexes from reaching divergent fitness optima. Additionally, biochemical and molecular work have revealed a variety of less easily observed phenotypes that nonetheless exhibit profound dimorphism. Sex‐specific selection could act on these more subtle, less visible, traits. We investigate sex‐specific selection in the polygynandrous dusky pipefish (Syngnathus floridae), which lacks distinct secondary sexual characteristics such as size, colour and morphological dimorphism. Using experimental breeding populations, we revealed that although males and females have similar opportunities for sexual selection, only males experience significant sexual selection pressures on body size. We also investigated patterns of sex‐biased and sex‐specific gene expression in gonads, livers and gills, and tested whether genes with highly divergent expression patterns between the sexes are more likely to be tissue‐specific, and therefore relieved of genetic constraints. Sex bias in gene expression was widespread, although the reproductive organs had the most sex‐biased and sex‐specific genes. Sex‐specific selection on gene expression in gills was primarily related to immune response, whereas the liver and gonads had a wide variety of cellular processes, as well as reproductive proteins, showing sex‐biased expression. These sex‐biased genes showed higher organ‐specificity in their expression patterns, suggesting that pleiotropic constraints might have historically impacted the evolution of sex‐specific expression patterns. Altogether, we find evidence for ongoing and historical sex‐specific selection in the dusky pipefish. [ABSTRACT FROM AUTHOR]

Females control the paternity of their offspring by selectively mating with males they perceive to be of high quality. In species where females mate with multiple males in succession, females may bias offspring paternity by favoring the sperm of one male over another, a process known as cryptic female choice. 1 While evidence of cryptic female choice exists in multiple taxa, the mechanisms underlying this process have remained difficult to unravel. 2 Understanding cryptic female choice requires demonstration of a female-driven post-mating bias in sperm use and paternity and a causal link between this bias and male cues. 3 In this study, we present evidence of cryptic female choice in female Drosophila melanogaster. Through experiments utilizing transgenic males expressing fluorescent sperm, we observed that exposure to attractive males between matings prompts females to expel the ejaculate of their initial mate more rapidly than in the presence of less attractive males. While doing so, females exhibit a bias in sperm storage against their first mate, thereby favoring the paternity of their subsequent mate. Our findings reveal that females adjust the timing of ejaculate expulsion in response to male pheromones in their environment, specifically heptanal and 11- cis -vaccenyl acetate, which are sensed by females through specific odorant receptors. We provide a cryptic female choice mechanism allowing a female to modulate the share of paternity of her first mate depending on the sensing of the quality of potential mates in her environment. These findings showcase that paternity can be influenced by events beyond copulation. [Display omitted] • D. melanogaster females exert cryptic mate choice • Females eject their first mate's ejaculate faster in the presence of attractive males • Females exposed to attractive males bias sperm storage against their first mate • Male pheromones heptanal and cVA are sufficient to shorten ejection latency Doubovetzky et al. present evidence of cryptic female choice in Drosophila melanogaster. Females exposed to pheromones of attractive males expedite ejaculate ejection from their first mate, favoring subsequent mates' sperm. This work highlights that female fruit flies can influence paternity of their offspring through post-copulatory mechanisms. [ABSTRACT FROM AUTHOR]

The process of reproductive character displacement involves divergence and/or the narrowing of variance in traits involved in species recognition, driven by interactions between taxa. However, stabilizing sexual selection may favor stasis and species similarity in these same traits if signals are optimized for transmission through the prevailing environment. Further, sexual selection may promote increased variability within species to facilitate individual recognition. Here we ask how the conflicting selection pressures of species recognition and sexual selection are resolved in a genus of Himalayan birds that sing exceptionally similar songs. We experimentally show that small differences in two traits (note shape and peak frequency) are both necessary and sufficient for species recognition. Song frequency shows remarkable clinal variation along the Himalayan elevational gradient, being most divergent where species co-occur, the classic signature of reproductive character displacement. Note shape shows no such clinal variation but varies more between individuals of an allopatric species than it does among individuals within species that co-occur. We argue that the different note shapes experience similar transmission constraints, and differences produced through species interactions spread back through the entire species range. Our results imply that reproductive character displacement is likely to be common. [ABSTRACT FROM AUTHOR]

Sexual selection predicts that males invest in sperm competition when females mate with multiple males. Because group residency facilitates access to mates, we hypothesized that variation in within-group mate competition influences investment in sperm competition. Verreaux's sifaka (Propithecus verreauxi) live in both single and multimale groups, allowing us to test the effect of within-group sperm competition on testes size. We predicted that dominant males living in multimale groups have larger testes than males in single-male groups. We also predicted that within multimale sifaka groups, dominant males have larger testes than subordinate males, due to either reproductive suppression or alternative mating tactics. We collected testes size and body mass from 23 adult male sifaka across 56 captures at the Ankoatsifaka Research Station in Kirindy Mitea National Park in western Madagascar from 2006 to 2019. Consistent with our predictions, we found that dominant males in multimale groups had significantly larger estimated testes mass than males in single-male groups. Within multimale groups, dominant males had significantly larger estimated testes mass than subordinate males. Males observed living in both conditions (multimale and single-male groups) exhibited larger estimated testes mass when they were dominant males in multimale groups than when in single-male groups. Sperm competition is typically examined via interspecific comparisons of testes size and mating system. Our study shows a similar pattern within the same species and a single population of wild primates. Our results show that (1) males flexibly respond to the current level of within-group sperm competition, and (2) within-group contest competition impacts male investment in sperm competition. [ABSTRACT FROM AUTHOR]

Despite having >1200 described species and despite their nearly worldwide distribution and prevalence in many xeric ecosystems, relative to many other arachnid groups, we know little about the natural history and behaviour of animals in the order Solifugae (camel spiders, sun spiders, sun scorpions, etc.). Here, we review the current solifuge literature through the lens of conceptual research areas in ecology, evolution, and behaviour and propose ways in which solifuges can contribute to research in specific subfields, as follows: (i) ecology: community and trophic dynamics; connecting food webs; habitat specialization; and biodiversity and conservation; (ii) evolution: speciation and diversification; activity cycles and associated traits; adaptations for speed; and living in extreme environments; and (iii) behaviour and sensory systems: sleep, quiescence, and diapause; sensory systems and sensory ecology; learning and cognition; and mating systems, sexual selection, and sexual conflict. This resource can provide a starting point for identifying research programmes that will simultaneously contribute basic natural history information about this under-studied group and provide a broader understanding of fundamental concepts and theories across the life sciences. We hope that scientists will take this review as a challenge to develop creative ways of leveraging the unique features of solifuges to advance scientific knowledge and understanding. [ABSTRACT FROM AUTHOR]

Animal coloration is often shaped by a myriad of factors that lead to differences in colour through changes in the chromatophores. Depending on how this variation is partitioned, coloration is often categorized as continuous or polymorphic. However, the boundaries between these two categories are not always clear. Here, we investigated whether the ventral coloration of the Madeiran wall lizard (Teira dugesii) varies continuously or corresponds to discrete colour morphs, via by-eye colour classification and visual modelling. By combining these two approaches, we show that T. dugesii coloration varies continuously and that colour classifications based on anthropomorphic approaches alone are ill suited to describe animal coloration. We also tested the influence of size, body condition, and sex as possible factors that might explain differences in T. dugesii coloration. We found that body condition, and especially size and sex, explain a great proportion of the variability observed in this species. These differences point to an effect of ontogeny, which might play a major role in colour development owing to the longevity of this species. Moreover, the sexual dichromatism that this species shows is indicative of an effect of sexual selection on coloration, perhaps explained by differences in circulating hormones. [ABSTRACT FROM AUTHOR]

The viviparity-driven conflict hypothesis postulates that the evolution of matrotrophy (postfertilization maternal provisioning) will result in a shift from a pre- to postcopulatory mate choice and thus accelerate the evolution of postcopulatory reproductive isolation. Here, we perform artificial insemination experiments on Heterandria formosa , a matrotrophic poeciliid fish, to probe for evidence of postcopulatory female choice. We established laboratory populations from Wacissa River (WR) and Lake Jackson (LJ). The WR females normally produce larger offspring than the LJ females. We artificially inseminated females with sperm from each population or from both populations simultaneously. When LJ females were inseminated with sperm from WR and LJ males, they allocated fewer resources to WR-sired offspring than when they were inseminated with WR sperm alone. The LJ females carrying developing offspring sired by males from different populations were thus able to discriminate against non-resident males when allocating resources to developing young. The WR females, which normally produce larger offspring than LJ females, did not discriminate among males from different localities. These findings provide insights into the ability of females from one population to exercise a form of postcopulatory mate selection. [ABSTRACT FROM AUTHOR]

Reproductive traits that mediate differential fitness associated with mate acquisition and fertilisation success are often strongly linked to the overall condition. We investigated the effects of resource quality and parental provisioning in the phenotypic expression of sexual and non‐sexual traits in a rainforest dung beetle, Onthophagus c.f. babirussa (Eschscholtz, 1822) from Singapore. F1 individuals were reared from wild‐caught beetles and paired up to produce offspring (F2), and F2 larvae from the same F1 parents were reared on two dung substrates (herbivore and omnivore) in a full‐sib design. Sexual traits displayed greater phenotypic variation in response to dung resource quality, with the precopulatory trait (horn length) responding more than the postcopulatory trait (testes weight). Notably, genotype‐by‐environment interactions between parental lines (genotype) and dung type (environment) affected male body size and horn length only, suggesting sex‐specific variance in plasticity associated with sexually selected precopulatory traits. Dung type had significant effects on all measured traits. Offspring that were provisioned higher quality resource (omnivore dung) had larger absolute and relative trait values. Parental lines only significantly affected female body size but none of the male traits, suggesting an important role of environment and resource partitioning in determining precopulatory success of male offspring. Parental provisioning of larval resource varied with resource quality and brood sequence. Parents provisioned more dung when herbivore dung was presented than when they were given omnivore dung and provisioned more dung for their earlier broods when using herbivore dung but not omnivore dung. This suggests a trade‐off between early offspring fitness and resource quality. We tested directly for genotype‐by‐environment (G × E) interactions in the expression of several morphological traits relevant to dung beetle fitness and documented that offspring with similar phenotypes may result from completely different parental resource allocation strategies. We discuss the importance of studying parental investment on trait variation and its implications on dung beetle ecology. [ABSTRACT FROM AUTHOR]

Sexual selection is not a single process. Instead, multiple processes of sexual selection can interact with respect to a given phenotype, in either reinforcing, independent, or conflicting directions. Here we consider how different processes of sexual selection interact in the seed bug Lygaeus simulans. This species is characterised by limited pre‐copulatory sexual selection, but the potential for rather strong post‐copulatory sexual selection. In particular, mating failure is common in this species, with around 40%–60% of copulations failing to result in the successful transfer of sperm. Mating failure is negatively correlated with female size, with smaller females being less likely to end up inseminated. We have recently argued that this pattern is best explained by cryptic male mate choice for large, more fecund females. Males therefore preferentially inseminate larger females. Here we explore how this potential cryptic male choice interacts with another component of post‐copulatory sexual selection: sperm competition. We first manipulated male and female size variation, generating large and small, male and female, size classes. Using a visible mutant marker to assign paternity, we then double‐mated females with males, in all combinations of male and female size. Our results showed that sperm competition outcomes were primarily driven by copulation duration, with longer copulations leading to greater paternity share for a male. We also confirmed that larger females are more likely to produce offspring than smaller females, as predicted by cryptic male choice for large females. This effect was again linked to copulation duration, with longer copulations less likely to lead to mating failure. While larger males tended to be more successful in sperm competition, especially if copulating second, female size had little effect on paternity, suggesting that cryptic male choice and sperm competition are acting relatively independently in this species. [ABSTRACT FROM AUTHOR]

Male‐biased sexual size dimorphism (SSD) is common in ungulates. The dominant scenario for the evolution of ungulate SSD suggests that habitat openness leads to greater SSD by increasing group size and thus sexual selection through male–male competition for mates. At a more proximate level, adaptive changes in SSD may result from the plastic response of individuals to environmental variation. In this study, we used 161,948 body mass data from a seasonally size‐dimorphic species, the northern chamois Rupicapra rupicapra, to examine the role of forest cover and other environmental variables in the expression of SSD. Data were collected from individuals hunted in the Austrian Alps, grouped into 28 mountain ranges with different forest cover, geological substrate and population density. Population‐specific growth curves were fitted using monomolecular models, and SSD was calculated as the log‐transformed ratio of male to female asymptotic body mass. A path model in which environmental factors indirectly influenced SSD via male or female body mass suggested that SSD increased with increasing density via reduced female body mass and decreased on siliceous substrates via reduced male body mass. Forest cover was negatively associated with body mass in both sexes, but not with variation in SSD. [ABSTRACT FROM AUTHOR]

Novel host plants are incorporated into the diets of phytophagous insects when females oviposit and juveniles feed and survive on them. A change in diet, however, can have morphological consequences. We recently found a population of the leaf‐footed cactus bug, Narnia femorata (Hemiptera: Coreidae), a historical cactus specialist, living and feeding on Cirsium thistle. We also found adults breeding and males using their enlarged hind legs (i.e., weapons) in male–male combat on thistle. When we compared this thistle population with a population feeding on cactus, we found that both populations had similar body and weapon sizes as well as weapon composition. However, the population living on thistle had longer mouthparts than the population found on cactus, although this difference only occurred at larger body sizes. This difference in adult mouthpart size is likely a result of the juvenile rearing environment (i.e., thistle or cactus). However, genetic differences may also affect this trait. Our results provide some interesting avenues for future research (e.g., a reciprocal transplant experiment) in a species with a recent host range expansion. [ABSTRACT FROM AUTHOR]

A preference for mating with conspecifics over heterospecifics is fundamental to the maintenance of species diversity in sexually reproducing organisms. This type of positive assortative preference results in sexual isolation, and a reduction in gene flow between species due to differences in mate choice. The proximate and ultimate causes of sexual isolation therefore constitute active areas of research in evolutionary biology. Sexual isolation is often stronger between closely related sympatric species as compared to allopatric species because of processes such as reinforcement. In addition, traditional theories of sexual selection suggest that because reproduction is more costly to females, they should be the choosier sex and play a more central role in sexual isolation. We conducted a comparative analysis of assortative mate preferences in males and females of sympatric and allopatric species pairs of darters (fish genus Etheostoma). We performed a meta‐analysis of 17 studies, encompassing 21 species, in which assortative preference was measured when fish were (in most cases) allowed only visual information. As expected, we found stronger preferences for conspecifics over heterospecifics across studies and species. However, we did not find an effect of sympatry or sex on the strength of preference for conspecifics, but rather remarkable variation across species. We offer several testable hypotheses to explain the variation we observed in the strength of assortative preference. [ABSTRACT FROM AUTHOR]

Wild boar (Sus scrofa) populations are increasing worldwide, leading to health, economic and conservation issues. Assessing genetic structure and diversity can aid in the effective monitoring and management of wild boar populations. Processes related to sexual selection and behavioral differences between sexes support the importance of considering sex in measuring genetic diversity. In this study, we investigated the genetic diversity of wild boar in southwestern Spain by comparing multilocus heterozygosity (MLH) in males and females. We collected tissue samples from 142 culled individuals and 146 fetuses during routine hunting activities and used 16 microsatellite markers to quantify MLH. Paternity analyses were conducted to infer the genotypes of reproductive males. Our results indicated that the sampled individuals constituted a unique polygynandrous population without clear genetic structure. We found that males tended to exhibit lower MLH than females, with reproductive males showing significantly lower MLH than females. We discuss the selection and demographic processes that might explain our results. We highlight the importance of sex-balanced culling for population control, as well as the use of sex-balanced samples for monitoring genetic diversities. [ABSTRACT FROM AUTHOR]

Hybridization is predicted to occur most frequently in closely related species when one species is rare (scarcity of mates hypothesis) and when the rare species of a heterospecific pair is more likely to be female (sexual selection hypothesis). We studied hybridization in mixed breeding colonies of the Western Grebe (Aechmophorus occidentalis) and Clark's Grebe (A. clarkii) at Clear Lake, California, during 2011-2019. Of 203 mated pairs with at least one Clark's Grebe (the rarer species, attending 15% of nests), 77.3% were conspecific pairs, 20.7% were heterospecific pairs, and 2.0% comprised a Clark's Grebe paired with a presumed hybrid. The proportion of heterospecific pairs was no greater in smaller colonies or later during the breeding season, contradicting the scarcity of mates hypothesis. Of 42 heterospecific pairs, the Clark's Grebe was just as likely to be male (45.2%) as female (54.8%), contradicting the sexual selection hypothesis. Hybridization between these species more likely results from an error in sexual imprinting due to interspecific brood parasitism or from extra-pair copulations. [ABSTRACT FROM AUTHOR]

Socially plastic behaviours are widespread among animals and can have a significant impact on fitness. Here, we investigated whether the socially plastic responses of female Drosophila melanogaster can evolve in predictable ways following long-term manipulation of adult sex ratio and adult nutrient availability. Previous reports show that female D. melanogaster respond plastically to their same-sex social environment and lay significantly fewer eggs after mating when previously exposed to other females. In this study, we tested 2 hypotheses, using females drawn from lines with an evolutionary history of exposure to variation in adult sex ratio (male-biased, female-biased or equal sex ratio) and adult nutritional environment (high or low quality). The first was that a history of elevated competition in female-biased regimes would select for increased plastic fecundity responses in comparison to females from other lines. The second was that these responses would also be magnified under poor nutritional resource regimes. Neither hypothesis was supported. Instead, we found that plastic fecundity responses were retained in females from all lines and did not differ significantly across any of them. The lack of differences does not appear to be due to insufficient selection, as we did observe significant evolutionary responses in virgin egg-laying patterns according to sex ratio and nutritional regime. The lack of variation in the magnitude of predicted plasticity is consistent with the idea that the costs of maintaining plasticity are low, benefits high, and that plasticity itself can be relatively hard wired. Graphical Abstract [ABSTRACT FROM AUTHOR]