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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.

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]

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]

Colour polymorphism is an example of visible phenotypic variability that is often associated with ecological factors and may produce local adaptations. Small populations, particularly in islands, offer opportunities for evolutionary novelties, and are therefore of particular interest to the study of polymorphisms. Here we study the dynamics of female colour morphs in the damselfly Ischnura elegans in the Balearic Islands. We found that insular populations are small, show low density, low mating activity, and low androchrome frequency. Our surveys suggest that male harassment is a powerful force in the dynamics of this female-limited polymorphism, because high male densities result in lower presence of mature females around the water, where copulation takes place. Non-male-like (infuscans) females have higher mating frequency. Androchromes were rare (15%) in all populations, but the frequency of the two non-male like females (infuscans and aurantiaca) was reversed between islands, despite their geographical proximity. We found a possible novel morph, suggesting that insular conditions allow innovations. Fitness differences between the two non-male-like females of I. elegans are still understudied, because most previous research has concentrated on the maintenance of androchromes, and are therefore a priority for future research. [ABSTRACT FROM AUTHOR]

The features of the physical environment set the stage upon which sexual selection operates, and consequently can have a significant impact on variation in realized individual fitness, and influence a population's evolutionary trajectory. This phenomenon has been explored empirically in several studies using fruit flies (Drosophila melanogaster) which have found that changing the spatial complexity of the mating environment influenced male–female interaction dynamics, (re)mating rates, and realized female fecundities. However, these studies did not explore mating patterns, which can dramatically alter the genetic composition of the next generation, and frequently only compared a single, small "simple" environment to a single larger "complex" environment. While these studies have shown that broadly changing the characteristics of the environment can have big effects on reproductive dynamics, the plasticity of this outcome to more subtle changes has not been extensively explored. Our study set out to compare patterns of mating and courtship between large- and small-bodied males and females, and female fecundities in both a simple environment and 2 distinctly different spatially complex environments. We found that realized offspring production patterns differed dramatically between all 3 environments, indicating that the effects of increasing spatial complexity on mating outcomes are sensitive to the specific type of environmental complexity. Furthermore, we observed female fecundities were higher for flies in both complex environments compared those in the simple environment, supporting its role as a mediator of sexual conflict. Together, these results show that the union of gametes within a population can be greatly influenced by the specific spatial features of the environment and that while some outcomes of increased environmental complexity are likely generalizable, other phenomena such as mating patterns and courtship rates may vary from one complex environment to another. Graphical Abstract [ABSTRACT FROM AUTHOR]

How sex chromosomes evolve compared to autosomes remains an unresolved question in population genetics. Most studies focus on only a handful of taxa, resulting in uncertainty over whether observed patterns reflect general processes or idiosyncrasies in particular clades. For example, in female heterogametic (ZW) systems, bird Z chromosomes tend to evolve quickly but not adaptively, while in Lepidopterans they evolve adaptively, but not always quickly. To understand how these observations fit into broader evolutionary patterns, we explore Z chromosome evolution outside of these two well-studied clades. We utilize a publicly available genome, gene expression, population, and outgroup data in the salmon louse Lepeophtheirus salmonis , an important agricultural pest copepod. We find that the Z chromosome is faster evolving than autosomes, but that this effect is driven by increased drift rather than adaptive evolution. Due to high rates of female reproductive failure, the Z chromosome exhibits a slightly lower effective population size than the autosomes which is nonetheless to decrease efficiency of hemizygous selection acting on the Z. These results highlight the usefulness of organismal life history in calibrating population genetic expectations and demonstrate the value of the ever-expanding wealth of publicly available data to help resolve outstanding evolutionary questions. [ABSTRACT FROM AUTHOR]

How often males and females need to mate to maximize their fitness is a source of sexual conflict in animals. Sexual conflict over mating frequency can lead to antagonistic coevolution in which males employ tactics to coerce females into mating, while females resist or evade mating attempts by males. Here, we report on a novel burying behavior observed in female northern map turtles (Graptemys geographica) in Opinicon Lake, Ontario, Canada that appears to function as a tactic to avoid male detection during the mating season. Underwater videos indicated that females are heavily solicited during the mating season with over half the females being actively pursued by males. Biologgers indicated that females are less active and remain deeper than males during the mating season. Our data strongly suggest that female northern map turtles avoid intense solicitation and potential harassment by males by burying themselves in lake sediments. This behavior appears to be a low‐cost solution for females to reduce the costs of resistance and mating while they are constrained to habitats with high male densities for overwintering. [ABSTRACT FROM AUTHOR]

External female genital mutilation (EFGM) is the strategy employed by male spiders to ensure paternity during sexual conflict over female remating. Three orb-web spider species have been identified to engage in EFGM, wherein males remove the female's genital scape, which is crucial for successful genital coupling. Mutilated females lose their remating ability. Despite the apparent fitness advantage of mutilator males over non-mutilators, mutilation success rates vary across these species. The extent to which females engage in aggression and sexual cannibalism as potential countermeasures against EFGM is also variable. In this study, two consecutive staged matings were conducted in Cyclosa confusa and C. vallata spiders to determine the rate of successful mutilation and the influence of sexual cannibalism and female aggression. Both species exhibited low rates of sexual cannibalism and female aggression. While most matings involving unmated C. vallata females resulted in successful mutilation, one-third of C. confusa females retained an intact scape after mating. Additionally, mutilation rates in C. confusa increased with male size and weight and decreased with female weight. In contrast to previous studies on other species, our results revealed low mutilation success with low sexual cannibalism and female aggression in C. confusa. [ABSTRACT FROM AUTHOR]

Abstract Sexual conflict arises from differences in reproductive interests between the sexes. We allowed the female harvestman Phalangium opilio to sequentially mate with two different males to examine female sexual receptivity in this species. Virgin females were more sexually receptive than non-virgins. Males exhibited a high interest in repeated copulations with the same female, often engaging in aggressive behaviours such as biting and reversed sexual cannibalism. Fellatio, a behaviour in which females lick the male’s penis, was observed in 44% of trials and was associated with female unwillingness to mate and shorter copulation duration. Fellatio was repeatable, suggesting that it is influenced by individual characteristics or underlying physiological factors. Female lifespan was negatively correlated with the total number of eggs produced, suggesting a trade-off between reproduction and longevity. These findings provide evidence of the appearance of fellatio, a female mating strategy that evolved as compensation of avoiding unwanted sexual intercourse.

Abstract Background Male courtship investment may evolve in response to the male’s expectation of future mating opportunities or the degree of female control during mating interactions. We used a comparative approach to test this hypotheses by assessing the courtship and mating behaviors of five widow spider species (genus Latrodectus) under common laboratory conditions. We predicted male investment in courtship would be higher in species where males mate only once because of high cannibalism rates (monogyny, L. geometricus, L. hasselti, L. mirabilis), compared to species with rare cannibalism (L. mactans, L. hesperus) in which males should reserve energy for future mating opportunities. Increased male investment, measured as courtship duration, might also evolve with increased female control over mating outcomes if females prefer longer courtships. We tested this by assessing the frequency of copulations, timing of sexual cannibalism, and the degree of female-biased size dimorphism, which is expected to be negatively correlated with the energetic cost of rebuffing male mating attempts. Results Copulation frequency was consistently lower in species with extreme female-skewed size dimorphism, and where sexual cannibalism was more prevalent, suggesting the importance of female control for mating outcomes. We confirmed significant interspecific variation in average courtship duration, but contrary to predictions, it was not predicted by male mating system, and there was no consistent link between courtship duration and sexual size dimorphism. Conclusion We show that the degree of sexual dimorphism is not only correlated with sexual cannibalism, but also with mating success since restriction of male copulation frequency by female Latrodectus affects paternity. However, predictions about male mating system or female control affecting courtship duration were not supported. We propose that the form of female control over mating and cannibalism, and male responses, might be more informative for understanding the evolution of courtship duration. For example, male tactics to avoid female aggression may drive lower courtship duration in species like L. mirabilis. Nonetheless, our results differ from inferences based on published studies of each species in isolation, illuminating the need for standardized data collection for behavioural comparative studies.

Linking reproductive fitness with adaptive traits at the genomic level can shed light on the mechanisms that produce and maintain sex‐specific selection. Here, we construct a multigenerational pedigree to investigate sex‐specific selection on a maturation gene, vgll3, in a wild Atlantic salmon population. The vgll3 locus is responsible for ~40% of the variation in maturation (sea age at first reproduction). Genetic parentage analysis was conducted on 18,265 juveniles (parr) and 685 adults collected at the same spawning ground over eight consecutive years. A high proportion of females (26%) were iteroparous and reproduced two to four times in their lifetime. A smaller proportion of males (9%) spawned at least twice in their lifetime. Sex‐specific patterns of reproductive fitness were related to vgll3 genotype. Females showed a pattern of overdominance where vgll3*EL genotypes had three‐fold more total offspring than homozygous females. In contrast, males demonstrated that late‐maturing vgll3*LL individuals had two‐fold more offspring than either vgll3*EE or vgll3*EL males. Taken together, these data suggest that balancing selection in females contributes to the maintenance of variation at this locus via increased fitness of iteroparous vgll3*EL females. This study demonstrates the utility of multigenerational pedigrees for uncovering complex patterns of reproduction, sex‐specific selection and the maintenance of genetic variation. [ABSTRACT FROM AUTHOR]

Sexual conflict is prevalent among animals and is primarily caused by the fact that the optimal mating rates are often higher in males than in females. While there is a growing appreciation that females can also gain from multiple matings, we still know relatively little about which sex controls the observed mating rates and how close it is to the optimal female mating rates. To address this issue, we tracked female bed bugs (Cimex lectularius) inseminated daily versus weekly and found that weekly inseminated females lived longer and produced over 50% more offspring. In a follow-up experiment employing a social network framework, we placed 24 bed bugs into a semi-naturalistic arena and recorded all sexual interactions. While recently inseminated females did not avoid males more often, they were more frequently rejected by males. Finally, we tracked avoidance behaviour in a single cohort of female bed bugs as they received six successive daily inseminations. Avoidance rates increased and insemination durations decreased with increasing number of prior inseminations. Overall, our results indicate high costs of polyandry. Although females possess some plastic avoidance strategies, the observed rates of insemination fall closer to the male rather than female optimum. [ABSTRACT FROM AUTHOR]

An advantage of sex chromosomes may be the potential to reduce sexual conflict because they provide a basis for selection to operate separately on females and males. However, evaluating the relationship between sex chromosomes and sexual conflict is challenging owing to the difficulty in measuring sexual conflict and substantial divergence between species with and without sex chromosomes. We therefore examined sex‐biased gene expression as a proxy for sexual conflict in three sets of Drosophila species with and without young sex chromosomes, the so‐called neo‐sex chromosomes. In all sets, we detected more sex‐biased genes in the species with neo‐sex chromosomes than in the species without neo‐sex chromosomes in larvae, pupae, and adult somatic tissues but not in gonads. In particular, many unbiased genes became either female‐ or male‐biased after linkage to the neo‐sex chromosomes in larvae, despite the low sexual dimorphism. For example, genes involved in metabolism, a key determinant for the rate of development in many animals, were enriched in the genes that acquired sex‐biased expression on the neo‐sex chromosomes at the larval stage. These genes may be targets of sexually antagonistic selection (i.e., large size and rapid development are selected for in females but selected against in males). These results indicate that acquiring neo‐sex chromosomes may have contributed to a reduction in sexual conflict, particularly at the larval stage, in Drosophila.. [ABSTRACT FROM AUTHOR]

While numerous studies have confirmed sexual selection for ornamental traits in animals, it remains unclear about how animals exaggerate ornamentation across traits. I found that some Asian barn swallows Hirundo rustica gutturalis possessed "pseudo‐tail spots" on their undertail coverts adjacent to a well‐known sexual signal, the white tail spots. A close inspection showed their remarkable resemblance, and, as a consequence, pseudo‐tail spots appear to add white spots to the uniformly black central tail feathers, increasing the total number and area of white spots when spread tails are viewed from below. Pseudo‐tail spots on the undertail covers do not incur any flight cost, unlike the white tail spots on the tail itself, and thus presence of pseudo‐tail spots can represent an initial stage of a deceptive elaboration as predicted by sexual selection theory (i.e., males can elaborate traits with no additional flight cost, uncoupling flight cost and trait expression). The frequency of pseudo‐tail spots in the study population remained low even a decade after the first observation (ca. 7%), but was higher compared to other populations (e.g., 1% in another Japanese population). The slow progress of evolution, perhaps due to the low detectability of the trait, provides a unique opportunity to observe contemporary evolution of ornament exaggeration across traits. Further research with wider spatial and temporal coverage is needed to better understand the evolutionary and ecological importance of the trait. [ABSTRACT FROM AUTHOR]

Sexually cannibalized males incur a significant fitness cost due to the loss of future mating opportunities and are expected to evolve behaviors to avoid or compensate for such costs. For example, partially cannibalized males may exhibit mate guarding, in which they accompany the female to prevent her from mating with another male. In some species, cannibalized males prolong the duration of copulation. However, little is known about the adaptive significance of the mating behavior of sexually cannibalized males. We hypothesized that mating itself serves a mate guarding function, and that behavioral change caused by cannibalism enhances the mate guarding function. We tested these hypotheses using the polyandrous and sexually cannibalistic praying mantid Tenodera angustipennis, with decapitation as a model of sexual cannibalism. We compared latencies to female mating with a rival male among three experimental treatments: unmated treatment, noncannibalistic mating treatment, and cannibalistic mating treatment. Mating itself delayed female remating, revealing its function in mate guarding. Decapitated males exhibited a higher guarding efficiency against rival males via firmer genital coupling. In addition, spermatophore attached to the female genital opening also delayed female remating, revealing an additional function in postmating mate guarding. Although copulation was prolonged due to decapitation, mating by a rival male was not delayed compared to noncannibalistic mating, probably because of weaker postcopulatory guarding. These findings suggest that greater mate guarding by decapitated males during copulation was offset by processes after copulation. Significance statement: Sexually cannibalized males die and lose the chance for future mating. This means that males that can avoid or compensate for this fitness loss may be favored. We examined this possibility by focusing on the postmating behavior of sexually cannibalized male mantises. Experimental analysis revealed that cannibalized males grasped the female more firmly during copulation to avoid disruption by other males, and prolonged copulation duration compared with noncannibalized males. These behavioral changes by cannibalized males contributed to delaying female remating with other males to the same extent as noncannibalized males. This suggests that sexually cannibalized males did not fully compensate for the loss of future mating opportunities. Stronger mate guarding via firm genital coupling and prolonged copulation duration in cannibalized males may be offset by weaker postcopulatory guarding such as shorter duration of copulatory plug attachment. [ABSTRACT FROM AUTHOR]

Active forms of cannibalism that involve predation of live conspecifics occur widely among amphibians, most notably by tadpoles that feed on each other and adults that feed on juveniles. In contrast, cannibalism among amphibian adults (adult–adult cannibalism) is less often reported and there have been no investigations on the occurrence of sexual cannibalism in this group to date. In this study, we present an observation of potential sexual cannibalism involving an adult female green and golden bell frog, Litoria aurea, preying on a conspecific adult male during the species' breeding season. By comparing our observation to the available literature, we show that adult–adult cannibalism among amphibians is rare but tends to be committed by females against their male counterparts. We thus suggest that the occurrence of sexual cannibalism should be extended to include this group, where sexual size dimorphism occurs widely among adults that congregate spatially during breeding periods, both predictors of intra‐specific predation. We hypothesise that amphibian females may be able to exploit male advertisement calls to differentiate suitable partners from potential prey and that male individuals are vulnerable to sexual cannibalism as they must risk attracting and physically exposing themselves to females in order to reproduce. Our findings reveal the complex dynamics that exist within adult amphibian populations, suggesting that females may have a choice when deciding how to interact with and utilise their male counterparts. As our findings are preliminary, based on a small sample size of records, including several from captive individuals, we encourage authors to publish their observations of cannibalism in the field, including unsuccessful attempts, to confirm the presence of sexual cannibalism in this group. [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]

Female fritillary butterflies (Lepidoptera: Nymphalidae: Argynnini) are known to have diversified genital structures, especially at the entrance of the bursa copulatrix. However, the origin and function of such elaborated structures are poorly known to date. We examined the male and female genital structures of six Japanese species selected from five genera/subgenera [Argynnis (Argynnis), Argynnis (Damora), Argynnis (Argyronome), Fabriciana, and Speyeria] of the Argynnini tribe and found that traumatic copulation is widespread in Argynnini. Various male genital structures, such as the uncus, valva, and phallus, can cause wounds to the female genitalia. The eighth venter of the female, where the highest morphological diversity in female genitalia was detected, is hooked and held by the male uncus during copulation. It is very likely that the diversified female genital structure coevolved with the male uncus as a counterpart for traumatic coupling. [ABSTRACT FROM AUTHOR]

Sexual conflict is a thriving area of animal behaviour research. Yet parallel research in the evolutionary human sciences remains underdeveloped and has become mired by controversy. In this special collection, we aim to invigorate the study of fitness-relevant conflicts between women and men, advocating for three synergistic research priorities. First, we argue that a commitment to diversity is required to innovate the field, achieve ethical research practice, and foster fruitful dialogue with neighbouring social sciences. Accordingly, we have prioritised issues of diversity as editors, aiming to stimulate new connections and perspectives. Second, we call for greater recognition that human sex/gender roles and accompanying conflict behaviours are both subject to natural selection and culturally determined. This motivates our shift in terminology from sexual to gendered conflict when addressing human behaviour, countering stubborn tendencies to essentialise differences between women and men and directing attention to the role of cultural practices, normative sanctions and social learning in structuring conflict battlegrounds. Finally, we draw attention to contemporary policy concerns, including the wellbeing consequences of marriage practices and the gendered implications of market integration. Focus on these themes, combined with attendance to the dangers of ethnocentrism, promises to inform culturally sensitive interventions promoting gender equality worldwide.

Parents confront multiple aspects of offspring demands and need to coordinate different parental care tasks. Biparental care is considered to evolve under circumstances where one parent is not competent for all tasks and cannot efficiently raise offspring. However, this hypothesis is difficult to test, as uniparental and biparental care rarely coexist. Chinese penduline tits (Remiz consobrinus) provide such a system where both parental care types occur. Here, we experimentally investigated whether parents in biparental nests are less capable of caring than parents in uniparental nests. We monitored parenting efforts at (1) naturally uniparental and biparental nests and (2) biparental nests before and during the temporary removal of a parent. Given the relatively small sample sizes, we have employed various statistical analyses confirming the robustness of our results. We found that total feeding frequency and brooding duration were similar for natural uniparental and biparental nests. Feeding frequency, but not brooding duration, contributed significantly to nestling mass. In line with this, a temporary parental removal revealed that the remaining parents at biparental nests fully compensated for the partner's feeding absence but not for brooding duration. This reflects that the manipulated parents are confronted with a trade‐off between feeding and brooding and were selected to invest in the more influential one. However, such a trade‐off may not occur in parents of natural uniparental care nests. The different capabilities of a parent independently coordinating feeding and brooding tasks suggest that parents from biparental and uniparental nests were exposed to different resource conditions, thereby foraging efficiency may differ between care types. [ABSTRACT FROM AUTHOR]

Living in groups can provide essential experience that improves sexual performance and reproductive success. While the effects of social experience have drawn considerable scientific interest, commonly used behavioral assays often do not capture the dynamic nature of interactions within a social group. Here, we conducted 3 experiments using a social network framework to test whether social experience during early adulthood improves the sexual competence of bed bugs (Cimex lectularius) when placed in a complex and competitive group environment. In each experiment, we observed replicate groups of bed bugs comprising previously socialized and previously isolated individuals of the same sex, along with an equal number of standardized individuals of the opposite sex. Regardless of whether we controlled for their insemination history, previously isolated males mounted and inseminated females at significantly higher rates than previously socialized males. However, we found no evidence of social experience influencing our other measures of sexual competence: proportion of mounts directed at females, ability to overcome female resistance, and strength of opposite-sex social associations. We similarly did not detect effects of social experience on our female sexual competence metrics: propensity to avoid mounts, rate of successfully avoiding mounts, opposite-sex social association strength, and rate of receiving inseminations. Our findings indicate that early social experience does not improve sexual competence in male and female bed bugs. [ABSTRACT FROM AUTHOR]

In most animals, body mass varies with ecological conditions and is expected to reflect how much energy can be allocated to reproduction and survival. Because the sexes often differ in their resource acquisition and allocation strategies, variations in adult body mass and their consequences on fitness can differ between the sexes.Assessing the relative contributions of environmental and genetic effects (i.e. heritability)—and whether these effects and their fitness consequences are sex‐specific—is essential to gain insights into the evolution of sexual dimorphism and sexual conflicts.We used 20+ years of data to study the sources of variation in adult body mass and associated fitness consequences in a bird with biparental care, the Alpine swift (Tachymarptis melba). Swifts appear monomorphic to human observers, though subtle dimorphisms are present.We first investigated the effects of weather conditions on adult body mass using a sliding window analysis approach. We report a positive effect of temperature and a negative effect of rainfall on adult body mass, as expected for an aerial insectivorous bird. We then quantified the additive genetic variance and heritability of body mass in both sexes and assessed the importance of genetic constraints on mass evolution by estimating the cross‐sex genetic correlation. Heritability was different from zero in both sexes at ~0.30. The positive cross‐sex genetic correlation and comparable additive genetic variance between the sexes suggest the possibility for evolutionary constraints when it comes to body mass. Finally, we assessed the sex‐specific selection on adjusted body mass using multiple fitness components. We report directional positive and negative selection trending towards stabilizing and diversifying selection on females and males respectively in relation to the weighted proportion of surviving fledglings.Overall, these results suggest that while body mass may be able to respond to environmental conditions and evolve, genetic constraints would result in similar changes in both sexes or an overall absence of response to selection. It remains unclear whether the weak (1%) dimorphism in Alpine swift body mass we report is simply a result of the similar fitness peaks between the sexes or of genetic constraints. [ABSTRACT FROM AUTHOR]

Fossilized mating insects are irreplaceable material for comprehending the evolution of the mating behaviours and life-history traits in the deep-time record of insects as well as the potential sexual conflict. However, cases of mating pairs are particularly rare in fossil insects, especially aquatic or semi-aquatic species. Here, we report the first fossil record of a group of water striders in copulation (including three pairs and a single adult male) based on fossils from the mid-Cretaceous of northern Myanmar. The new taxon, Burmogerris gen. nov., likely represents one of the oldest cases of insects related to the marine environment, such as billabongs formed by the tides. It exhibits conspicuous dimorphism associated with sexual conflict: the male is equipped with a specialized protibial comb as a grasping apparatus, likely representing an adaptation to overcome female resistance during struggles. The paired Burmogerris show smaller males riding on the backs of the females, seemingly recording a scene of copulatory struggles between the sexes. Our discovery reveals a mating system dominated by males and sheds light on the potential sexual conflicts of Burmogerris in the Cretaceous. It indicates the mating behaviour remained stable over long-term geological time in these water-walking insects. [ABSTRACT FROM AUTHOR]

Female spiders and praying mantises are renowned for their cannibalism of male partners before, during, or after mating. While several hypotheses have been proposed to explain species-specific examples of sexual cannibalism, much variation remains unexplained, including why the timing of cannibalism varies across taxa. Here, I outline how sexually cannibalistic behavior could evolve via sexually antagonistic selection as a type of behavioral resistance to male-imposed mating costs, and how such a generalizable interpretation provides a framework for understanding the evolution of both sexual cannibalism in females and anti-cannibalistic traits in males. I discuss how differences between mating systems that physiologically constrain males to mate only once (monogyny) or twice (bigyny) and systems where the sexes can potentially mate multiply (polygyny and polyandry) are likely to influence how sexual conflict shapes cannibalistic behavior. I review key examples from the literature that suggest how sexually cannibalistic behavior might function as a female resistance trait and provide comprehensive predictions for testing this hypothesis empirically. [ABSTRACT FROM AUTHOR]

Many genes are differentially expressed between males and females and patterns of sex-biased gene expression (SBGE) vary among species. Some of this variation is thought to have evolved in response to differences in mate competition among species that cause varying patterns of sex-specific selection. We used experimental evolution to test this by quantifying SBGE and sex-specific splicing in 15 Drosophila melanogaster populations that evolved for 104 generations in mating treatments that removed mate competition via enforced monogamy, or allowed mate competition in either small, simple, or larger, structurally more complex mating environments. Consistent with sex-specific selection affecting SBGE, initially sex-biased genes diverged in expression more among treatments than unbiased genes, and there was greater expression divergence for male- than female-biased genes. It has been suggested the transcriptome should be "feminized" under monogamy because of the removal of sexual selection on males; we did not observe this, likely because selection differs in additional ways between monogamy vs. polygamy. Significant divergence in average expression dimorphism between treatments was observed and, in some treatment comparisons, the direction of the divergence differed across different sex-bias categories. There was not a generalized reduction in expression dimorphism under enforced monogamy. [ABSTRACT FROM AUTHOR]

Males and females often exhibit different behaviours during mate acquisition, pair‐bonding and parenting, and a convenient label to characterize these behaviours is sex role. The diverse roles that male and female shorebirds (plovers, sandpipers and allies) exhibit in mating and parenting have played a key role in advancing mainstream theories in avian ecology and behavioural biology including sexual selection, sexual conflict and parental cooperation. Recent advances in shorebird research have also highlighted the significance of the social environment in driving sex role behaviours by linking the adult sex ratio with breeding behaviour and population demography. Here we review the key advances in sex role research using shorebirds as an ecological model system. We identify knowledge gaps and argue that shorebirds have untapped potential to accelerate diverse research fields including evolutionary genomics, movement ecology, social networks and environmental changes. Future studies of sex roles will benefit from individual‐based monitoring using advanced tracking technologies, and from multi‐team collaborations that are facilitated by standardized data collection methodologies across different species in the field. These advances will not only contribute to our understanding of reproductive strategies, but they will also have knock‐on effects on predicting population resilience to environmental changes and on prioritizing species for conservation. [ABSTRACT FROM AUTHOR]

While sexual size dimorphism (SSD) is abundant in nature, there is huge variation in both the intensity and direction of SSD. SSD results from a combination of sexual selection for large male size, fecundity selection for large female size and ecological selection for either. In most vertebrates, it is variation in the intensity of male–male competition that primarily underlies variation in SSD. In this study, we test four hypotheses regarding the adaptive value of SSD in sharks—considering the potential for each of fecundity, sexual, ecological selection and reproductive mode as the primary driver of variation in SSD between species. We also estimate past macroevolutionary shifts in SSD direction/intensity through shark phylogeny. We were unable to find evidence of significant SSD in early sharks and hypothesise that SSD is a derived state in this clade, that has evolved independently of SSD observed in other vertebrates. Moreover, there is no significant relationship between SSD and fecundity, testes mass or oceanic depth in sharks. However, there is evidence to support previous speculation that reproductive mode is an important determinant of interspecific variation in SSD in sharks. This is significant as in most vertebrates sexual selection is thought to be the primary driver of SSD trends, with evidence for the role of fecundity selection in other clades being inconsistent at best. While the phylogenetic distribution of SSD among sharks is superficially similar to that observed in other vertebrate clades, the relative importance of selective pressures underlying its evolution appears to differ. [ABSTRACT FROM AUTHOR]

In species that provide biparental care, there is a sexual conflict between parents over how much each should contribute toward caring for their joint offspring. Theoretical models for the resolution of this conflict through behavioral negotiation between parents assume that parents cannot assess their partner's state directly but do so indirectly by monitoring their partner's contribution. Here, we test whether parents can assess their partner's state directly by investigating the effect of nutritional state on cooperation between parents in the burying beetle Nicrophorus vespilloides. We used a two-by-two factorial design, in which a well-fed or food-deprived female was paired with a well-fed or food-deprived male. We found that females adjusted their level of care in response to both their own nutritional state and that of their partner and that these decisions were independent of their partner's contribution. We found no evidence that males responded directly to the nutritional state. Males instead responded indirectly based on the contribution of their partner. Our results suggest that parents are able to assess the state of their partner, in contrast to what has been assumed, and that these assessments play an important role in the mediation of sexual conflict between caring parents. [ABSTRACT FROM AUTHOR]

Abstract While numerous studies have confirmed sexual selection for ornamental traits in animals, it remains unclear about how animals exaggerate ornamentation across traits. I found that some Asian barn swallows Hirundo rustica gutturalis possessed “pseudo‐tail spots” on their undertail coverts adjacent to a well‐known sexual signal, the white tail spots. A close inspection showed their remarkable resemblance, and, as a consequence, pseudo‐tail spots appear to add white spots to the uniformly black central tail feathers, increasing the total number and area of white spots when spread tails are viewed from below. Pseudo‐tail spots on the undertail covers do not incur any flight cost, unlike the white tail spots on the tail itself, and thus presence of pseudo‐tail spots can represent an initial stage of a deceptive elaboration as predicted by sexual selection theory (i.e., males can elaborate traits with no additional flight cost, uncoupling flight cost and trait expression). The frequency of pseudo‐tail spots in the study population remained low even a decade after the first observation (ca. 7%), but was higher compared to other populations (e.g., 1% in another Japanese population). The slow progress of evolution, perhaps due to the low detectability of the trait, provides a unique opportunity to observe contemporary evolution of ornament exaggeration across traits. Further research with wider spatial and temporal coverage is needed to better understand the evolutionary and ecological importance of the trait.

Abstract An advantage of sex chromosomes may be the potential to reduce sexual conflict because they provide a basis for selection to operate separately on females and males. However, evaluating the relationship between sex chromosomes and sexual conflict is challenging owing to the difficulty in measuring sexual conflict and substantial divergence between species with and without sex chromosomes. We therefore examined sex‐biased gene expression as a proxy for sexual conflict in three sets of Drosophila species with and without young sex chromosomes, the so‐called neo‐sex chromosomes. In all sets, we detected more sex‐biased genes in the species with neo‐sex chromosomes than in the species without neo‐sex chromosomes in larvae, pupae, and adult somatic tissues but not in gonads. In particular, many unbiased genes became either female‐ or male‐biased after linkage to the neo‐sex chromosomes in larvae, despite the low sexual dimorphism. For example, genes involved in metabolism, a key determinant for the rate of development in many animals, were enriched in the genes that acquired sex‐biased expression on the neo‐sex chromosomes at the larval stage. These genes may be targets of sexually antagonistic selection (i.e., large size and rapid development are selected for in females but selected against in males). These results indicate that acquiring neo‐sex chromosomes may have contributed to a reduction in sexual conflict, particularly at the larval stage, in Drosophila..

Abstract Active forms of cannibalism that involve predation of live conspecifics occur widely among amphibians, most notably by tadpoles that feed on each other and adults that feed on juveniles. In contrast, cannibalism among amphibian adults (adult–adult cannibalism) is less often reported and there have been no investigations on the occurrence of sexual cannibalism in this group to date. In this study, we present an observation of potential sexual cannibalism involving an adult female green and golden bell frog, Litoria aurea, preying on a conspecific adult male during the species' breeding season. By comparing our observation to the available literature, we show that adult–adult cannibalism among amphibians is rare but tends to be committed by females against their male counterparts. We thus suggest that the occurrence of sexual cannibalism should be extended to include this group, where sexual size dimorphism occurs widely among adults that congregate spatially during breeding periods, both predictors of intra‐specific predation. We hypothesise that amphibian females may be able to exploit male advertisement calls to differentiate suitable partners from potential prey and that male individuals are vulnerable to sexual cannibalism as they must risk attracting and physically exposing themselves to females in order to reproduce. Our findings reveal the complex dynamics that exist within adult amphibian populations, suggesting that females may have a choice when deciding how to interact with and utilise their male counterparts. As our findings are preliminary, based on a small sample size of records, including several from captive individuals, we encourage authors to publish their observations of cannibalism in the field, including unsuccessful attempts, to confirm the presence of sexual cannibalism in this group.

One of the most pressing questions we face as biologists is to understand how climate change will affect the evolutionary dynamics of natural populations and how these dynamics will in turn affect population recovery. Increasing evidence shows that sexual selection favors population viability and local adaptation. However, sexual selection can also foster sexual conflict and drive the evolution of male harm to females. Male harm is extraordinarily widespread and has the potential to suppress female fitness and compromise population growth, yet we currently ignore its net effects across taxa or its influence on local adaptation and evolutionary rescue. We conducted a comparative meta-analysis to quantify the impact of male harm on female fitness and found an overall negative effect of male harm on female fitness. Negative effects seem to depend on proxies of sexual selection, increasing inversely to the female relative size and in species with strong sperm competition. We then developed theoretical models to explore how male harm affects adaptation and evolutionary rescue. We show that, when sexual conflict depends on local adaptation, population decline is reduced, but at the cost of slowing down genetic adaptation. This trade-off suggests that eco-evolutionary feedback on sexual conflict can act like a double-edged sword, reducing extinction risk by buffering the demographic costs of climate change, but delaying genetic adaptation. However, variation in the mating system and male harm type can mitigate this trade-off. Our work shows that male harm has widespread negative effects on female fitness and productivity, identifies potential mechanistic factors underlying variability in such costs across taxa, and underscores how acknowledging the condition-dependence of male harm may be important to understand the demographic and evolutionary processes that impact how species adapt to environmental change. [ABSTRACT FROM AUTHOR]

Rapid genitalia evolution is believed to be mainly driven by sexual selection. Recently, noncopulatory genital functions have been suggested to exert stronger selection pressure on female genitalia than copulatory functions. In bedbugs (Cimicidae), the impact of the copulatory function can be isolated from the noncopulatory impact. Unlike in other taxa, female copulatory organs have no function in egg-laying or waste-product expulsion. Males perform traumatic mating by piercing the female integument, thereby imposing antagonistic selection on females and suspending selection to morphologically match female genitalia. We found the location of the copulatory organ evolved rapidly, changing twice between dorsal and ventral sides, and several times along the anteroposterior and the left–right axes. Male genital length and shape varied much less, did not appear to follow the positional changes seen in females, and showed no evidence for coevolution. Female genitalia position evolved 1.5 times faster than male genital length and shape and showed little neutral or geographic signals. Instead, we propose that nonmorphological male traits, such as mating behavior, may drive female genitalia morphology in this taxon. Models of genitalia evolution may benefit from considering morphological genital responses to nonmorphological stimuli, such as male mating behavior or copulatory position. [ABSTRACT FROM AUTHOR]

Sexual selection is the differential reproductive success of individuals, resulting from competition for mates, mate choice, or success in fertilization. In primates, this selective pressure often leads to the development of exaggerated traits which play a role in sexual competition and successful reproduction. In order to gain insight into the mechanisms driving the development of sexually selected traits, we used an unbiased genome-wide approach across 21 primate species to correlate individual rates of protein evolution to relative testes size and sexual dimorphism in body size, 2 anatomical hallmarks of sexual selection in mammals. Among species with presumed high levels of sperm competition, we detected strong conservation of testes-specific proteins responsible for spermatogenesis and ciliary form and function. In contrast, we identified accelerated evolution of female reproductive proteins expressed in the vagina, cervix, and fallopian tubes in these same species. Additionally, we found accelerated protein evolution in lymphoid tissue, indicating that adaptive immune functions may also be influenced by sexual selection. This study demonstrates the distinct complexity of sexual selection in primates revealing contrasting patterns of protein evolution between male and female reproductive tissues. [ABSTRACT FROM AUTHOR]

In evolutionary ecology, coevolution is typically defined as reciprocal evolution of interacting species. However, outside the context of interacting species, the term “coevolution” is also used at levels of biological organization within species (e.g., between males and females, between cells, and between genes or proteins). Furthermore, although evolution is typically defined as “genetic change over time”, coevolution need not involve genetic changes in the interacting parties, since cultures can also evolve. In this review, I propose that coevolution be defined more broadly as “reciprocal adaptive evolution at any level of biological organisation”. The classification of reciprocal evolution at all levels of biological organization as coevolution would maintain consistency in terminology. More importantly, the broader definition should facilitate greater integration of coevolution research across disciplines. For example, principles usually discussed only in the context of coevolution between species or coevolution between genes (e.g., tight and diffuse coevolution, and compensatory coevolution, respectively) could be more readily applied to new fields. The application of coevolutionary principles to new contexts could also provide benefits to society, for instance in deducing the dynamics of coevolution between cancer cells and cells of the human immune system. [ABSTRACT FROM AUTHOR]

Mate choice is a critical decision with direct implications for fitness. Although it has been recognized for over 150 years, our understanding of its underlying mechanisms is still limited. Most studies on mate choice focus on the evolutionary causes of behavior, with less attention given to the physiological and molecular mechanisms involved. This is especially true for invertebrates, where research on mate choice has largely focused on male behavior. This review summarizes the current state of knowledge on the neural, molecular and neurohormonal mechanisms of female choice in invertebrates, including behaviors before, during, and after copulation. We identify areas of research that have not been extensively explored in invertebrates, suggesting potential directions for future investigation. We hope that this review will stimulate further research in this area. [ABSTRACT FROM AUTHOR]

In Atlantic salmon, age at maturation is a life history trait governed by a sex‐specific trade‐off between reproductive success and survival. Following environmental changes across large areas of the Northeast Atlantic, many populations currently display smaller size at age and higher age at maturation. However, whether these changes reflect rapid evolution or plasticity is unknown. Approximately 1500 historical and contemporary salmon from the river Etne in Western Norway, genotyped at 50,000 SNPs, revealed three loci associated with age at maturation. These included vgll3 and six6 which collectively explained 36%–50% of the age at maturation variation in the 1983–1984 period. These two loci also displayed sex‐specific epistasis, as the effect of six6 was only detected in males bearing two copies of the late maturation allele for vgll3. Strikingly, despite allelic frequencies at vgll3 remaining unchanged, the combined influence of these genes was nearly absent in all samples from 2013 to 2016, and genome‐wide heritability strongly declined between the two time‐points. The difference in age at maturation between males and females was upheld in the population despite the loss of effect from the candidate loci, which strongly points towards additional causative mechanisms resolving the sexual conflict. Finally, because admixture with farmed escaped salmon was excluded as the origin of the observed disconnection between gene(s) and maturation age, we conclude that the environmental changes observed in the North Atlantic during the past decades have led to bypassing of the influence of vgll3 and six6 on maturation through growth‐driven plasticity. see also the Perspective by Maren Wellenreuther [ABSTRACT FROM AUTHOR]

Sexual selection and the evolution of costly mating strategies can negatively impact population viability and adaptive potential. While laboratory studies have documented outcomes stemming from these processes, recent observations suggest that the demographic impact of sexual selection is contingent on the environment and therefore may have been overestimated in simple laboratory settings. Here we find support for this claim. We exposed copies of beetle populations, previously evolved with or without sexual selection, to a 10‐generation heatwave while maintaining half of them in a simple environment and the other half in a complex environment. Populations with an evolutionary history of sexual selection maintained larger sizes and more stable growth rates in complex (relative to simple) environments, an effect not seen in populations evolved without sexual selection. These results have implications for evolutionary forecasting and suggest that the negative demographic impact of sexually selected mating strategies might be low in natural populations. [ABSTRACT FROM AUTHOR]

Studies of parental care in tropical birds are still relatively scarce in comparison with northern temperate species, especially regarding to the division of parental tasks, leading to a biased and incomplete knowledge of avian reproductive strategies. Herein, we studied the sexual division of parental care in a sexually monomorphic Neotropical passerine, the Pale-breasted Thrush (Turdus leucomelas). We recorded food provisioning and food quantity rates (e.g. feeding trips/h and food items/h, respectively), nest sanitation rate (e.g. events of faecal sacs removal/h), and the time devoted to nest attendance and brooding behaviours by each parent. Throughout the 2015–2017 breeding seasons, we video-recorded 153.5 h of parental care in 33 nesting attempts by 26 breeding pairs in a suburban area of south-eastern Brazil. We found that males had higher food provisioning rates and delivered more food items to larger broods, while female did not respond to brood size. As expected, brood age positively affected food provisioning and food quantity rates of both sexes. Faecal sacs were removed predominantly by ingestion throughout the nesting stage, and males had higher nest sanitation rates. Nest attendance reached 34 ± 27% of the time and decreased with nestling age following a decrease in brooding behaviour, a female-only task, while males stayed in the nest for only 4 ± 4% of observation time. Although most of the parental activities are performed by both sexes, males and females differed in which tasks they invested the most, with brood size and brood age being important modulating factors. [ABSTRACT FROM AUTHOR]

Offspring desertion by a single parent, mainly the female, occurs in many charadriiform birds. According to the differential parental capacity hypothesis (DPCH), females are more likely to desert, since they may be in poorer body condition than males as a consequence of egg-laying costs. This study investigated the body condition of 122 male and 118 female Whiskered Terns. In this species half of females desert during the chick-rearing period, the remainder during the post-fledging period. Body condition was investigated during the late incubation and early chick-rearing phases during the biparental care period in: (1) females that deserted during the chick-rearing period, (2) females that did not desert during this time, (3) males deserted by females, and (4) males not deserted by females. Among females that stayed, body condition during the pre-hatching period did not vary with relative catching date (clutch/brood age), whereas females that later deserted showed a very poor body condition when caught around seven days prior to hatching. After hatching, body condition was lower in both deserting and non-deserting females caught later. Among males whose females stayed, body condition remained nearly stable, whereas the body condition of males whose females deserted was lower the later they were caught. These results tally only partially with the DPCH: the pattern of parental body condition changes during breeding is apparently more complex than assumed by the DPCH and the cost of egg laying may be lower than suggested. Desertion by Whiskered Tern females is better explained by the sex role differences in parental care. The male's ability to compensate for the missing female may be playing a role in the evolution of desertion. [ABSTRACT FROM AUTHOR]

Strong sexual selection frequently favors males that increase their reproductive success by harming females, with potentially negative consequences for natural populations. Understanding what factors modulate conflict between the sexes is hence critical to understand both the evolution of male and female phenotypes and the viability of populations in the wild. Here, we model the evolution of male harm while incorporating male-induced maternal effects on offspring quality. We show that because male harm can induce condition-transfer maternal effects that reduce the quality of a harming male's own offspring, maternal effects can partially align male and female evolutionary interests and significantly curb the evolution of male harm. These effects are independent of relatedness, the scale of competition, mating system, and whether male harm comes before (i.e. harassment) and/or during/after (i.e. traumatic inseminations or toxic ejaculates) mating and are particularly salient when maternal effects influence offspring ability to inflict (sons) or resist (daughters) harm. Our results underscore the potential importance of considering maternal effects to unravel the evolution of sexual conflict. [ABSTRACT FROM AUTHOR]

Whether sexual selection facilitates or hampers the ability to plastically respond to novel environments might depend on population structure, via its effects on sexual interactions and associated fitness payoffs. Using experimentally evolved lines of the seed beetle Callosobruchus maculatus , we tested whether individuals evolving under different sexual selection (monogamy vs. polygamy) and population spatial structure (metapopulation vs. undivided populations) treatments differed in their response across developmental thermal conditions (control, hot, or stressful) in a range of fitness and fitness-associated traits. We found that individuals from subdivided populations had lower lifetime reproductive success at hot temperatures, but only in lines evolving under relaxed sexual selection, revealing a complex interaction between sexual selection, population structure, and thermal environmental stress on fitness. We also found an effect of population structure on several traits, including fertility and adult emergence success, under exposure to high thermal conditions. Finally, we found a strong negative effect of hot and stressful temperatures on fitness and associated traits. Our results show that population structure can exacerbate the impact of a warming climate, potentially leading to declines in population viability, but that sexual selection can buffer the negative influence of population subdivision on adaptation to warm temperatures. [ABSTRACT FROM AUTHOR]

Natural selection is notoriously dynamic in nature, and so, too, is sexual selection. The interactions between phytophagous insects and their host plants have provided valuable insights into the many ways in which ecological factors can influence sexual selection. In this review, we highlight recent discoveries and provide guidance for future work in this area. Importantly, host plants can affect both the agents of sexual selection (e.g., mate choice and male–male competition) and the traits under selection (e.g., ornaments and weapons). Furthermore, in our rapidly changing world, insects now routinely encounter new potential host plants. The process of adaptation to a new host may be hindered or accelerated by sexual selection, and the unexplored evolutionary trajectories that emerge from these dynamics are relevant to pest management and insect conservation strategies. Examining the effects of host plants on sexual selection has the potential to advance our fundamental understanding of sexual conflict, host range evolution, and speciation, with relevance across taxa. [ABSTRACT FROM AUTHOR]

Males can bias insemination and fertilization in their favour by guarding females. In some species, males physically constrain females, while in others, female movement is not as directly controlled. In the Pacific field cricket Teleogryllus oceanicus , some males produce the same calling song used in long-distance mate attraction after spermatophore transfer, even though they cannot mate again. We tested the idea that this postcopulatory song serves as a mate-guarding tactic. Females that heard postcopulatory song were more likely to stay close to the male and retain their spermatophore, thus increasing the likelihood of the male fertilizing their clutch. To our knowledge, our results provide the first evidence of postcopulatory song in T. oceanicus and suggest that it may be an effective mate-guarding tactic. • Postcopulatory guarding increases insemination and likelihood of reproductive success. • In preliminary experiments, some male field crickets sang immediately after mating. • We examined the role of postcopulatory song as a mate-guarding tactic. • Postcopulatory song increased female spermatophore retention. • Postcopulatory song also increased female time spent in proximity to males. [ABSTRACT FROM AUTHOR]

There is a growing effort to understand how sexual selection varies over space and time under different ecological conditions and how this can maintain variation in sexual traits. An interesting ecological condition is population density, which can either increase or decrease sexual selection depending on the natural history of the species. We examined sexual and natural selection in an undescribed amphipod species (Hyalella sp.) using surveys of two natural populations that increase in density from spring to summer. We also conducted an experiment that directly manipulated density to assess the effects on sexual selection. In the field during spring (low density) and summer (high density), we documented sexual selection on male traits, including body size, gnathopods and antennae. We found that the magnitude and direction of this selection changed from spring to summer and that selection patterns differed between populations. In the experiment, we found no sexual selection occurred at low density, but found significant positive selection on all three male traits at medium and high densities. These results underline the importance of isolating individual ecological factors to determine their role in sexual selection while also documenting patterns in natural populations to understand how selection varies over space and time. [ABSTRACT FROM AUTHOR]

Vibrant male coloration and energetic courtship displays set jumping spiders apart from most arachnids, which typically rely on nonvisual stimuli. Like many other spiders, female salticids sometimes engage in precopulatory sexual cannibalism, making courtship a risky but necessary endeavour for males. In this study, we investigated the relationship between male coloration and female aggression to better understand the interplay of attraction and aversion during courtship. Many male jumping spiders sport conspicuous coloration or high-contrast patterns resembling those of many aposematic insects. The faces of Plexippus paykulli males are adorned with bold vertical stripes that are directed towards females during courtship. We hypothesized that, if spiders find stripes unappetizing in a foraging context, then male stripes might leverage this aversion to reduce the likelihood of sexual cannibalism. We tested whether spiders exhibit an aversion to stripes in the context of predation by manipulating prey coloration and testing spider preference for striped versus nonstriped prey. Then we conducted two courtship experiments by manipulating male facial coloration to determine whether the presence of male stripes affects female aggression and likelihood of mating. We also manipulated female foraging drive (diet or mating status) in each courtship experiment to see whether common sources of natural variation among females influenced response to courting males. We found that spiders showed an aversion to stripes while foraging but that this aversion did not confer reduced aggression towards striped males. Instead, female condition influenced female response to courting males, with hungrier females showing higher aggression and previously mated females being mounted less frequently than nonmated females. However, stripes did affect the likelihood of male reproductive success, as in one experiment, striped males mounted females more frequently than did nonstriped males and matings with striped males were more likely to lead to fertile eggs. Thus, stripes may confer advantages to males other than reduced female aggression. • Spiders avoided striped (versus grey) prey when given a choice. • Male facial stripes improved mating success but did not reduce female aggression. • Hungrier females were more aggressive towards courting males. • Females were less likely to mate if they had mated previously. [ABSTRACT FROM AUTHOR]

Abstract Parents confront multiple aspects of offspring demands and need to coordinate different parental care tasks. Biparental care is considered to evolve under circumstances where one parent is not competent for all tasks and cannot efficiently raise offspring. However, this hypothesis is difficult to test, as uniparental and biparental care rarely coexist. Chinese penduline tits (Remiz consobrinus) provide such a system where both parental care types occur. Here, we experimentally investigated whether parents in biparental nests are less capable of caring than parents in uniparental nests. We monitored parenting efforts at (1) naturally uniparental and biparental nests and (2) biparental nests before and during the temporary removal of a parent. Given the relatively small sample sizes, we have employed various statistical analyses confirming the robustness of our results. We found that total feeding frequency and brooding duration were similar for natural uniparental and biparental nests. Feeding frequency, but not brooding duration, contributed significantly to nestling mass. In line with this, a temporary parental removal revealed that the remaining parents at biparental nests fully compensated for the partner's feeding absence but not for brooding duration. This reflects that the manipulated parents are confronted with a trade‐off between feeding and brooding and were selected to invest in the more influential one. However, such a trade‐off may not occur in parents of natural uniparental care nests. The different capabilities of a parent independently coordinating feeding and brooding tasks suggest that parents from biparental and uniparental nests were exposed to different resource conditions, thereby foraging efficiency may differ between care types.