Men's use of internet pornography has been widely studied; however, the frequency with which men use different genres of pornography, and the individual differences associated with the use of different genres of pornography, has received less attention. The aim of the present research was to determine whether men's sociosexual orientation and personality traits were associated with use of different genres of internet pornography. Across three studies, men were asked to self-report the frequency with which they have used each genre of pornography (Study 1; n = 126), presented with video thumbnails representing the various genres of pornography and asked to self-report their interest in using each genre (Study 2; n = 166), and given brief descriptions for each genre and asked to report their interest in using each genre (Study 3; n = 169). These associations were examined using men's self-reported sociosexual orientation, personality traits, and use of four broad genres of pornography. Results indicated that aspects of men's sociosexual orientation and personality were correlated with men's use of various genres of pornography. Regression analyses revealed that aspects of men's sociosexual orientation and personality were uniquely predictive of their use of group sex pornography (which depicts cues to high levels of sperm competition), as well as female-specific and paraphilic pornography. Discussion considers the potential evolutionary psychological implications of these findings, as well as limitations and directions for future studies of pornography use.

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Léna Meunier is an author on ‘ Exploring the mechanisms underlying the last male precedence in the North African houbara bustard’, published in JEB. Léna is a Research assistant in the lab of Janaina Torres Carreira at Reneco International Wildlife Consultants, UAE, investigating Avian sperm competition and reproductive biology.

ABSTRACTSeminal fluid proteins (SFPs) can alter female physiology and behavior, with consequences that may align with or oppose female interests. Many SFPs are known to shape aspects of the female post‐mating response, yet evidence for direct effects on female fitness is scarce. In Drosophila melanogaster, the SFP Acp29AB is firmly linked to sperm defense (P1) and sperm storage, but its impacts on females are poorly understood. Using a GAL4–UAS RNAi system with perfectly matched genetic backgrounds, we manipulated Acp29AB gene expression either ubiquitously or specifically in the male accessory gland and then asked how knockdown alters male sperm competition and, in female mates, oviposition dynamics and competitive fitness. Both knockdowns impaired sperm defense, consistent with past work on Acp29AB. We uncovered a previously undetected effect on oviposition timing: across 14 days after a single mating, females mated to control males laid more eggs early in life than females mated to knockdown males, advancing the timing of reproduction. With accessory gland‐specific knockdown, this shift occurred without a change in total egg output, which may explain why earlier work focused on totals alone did not detect an effect. Despite accelerated oviposition in mates of control males, female competitive fitness in a five‐day, early‐life assay that included direct (female–female) and indirect (larval) competition did not differ between treatments. Thus, Acp29AB enhances male sperm defense and promotes earlier egg laying in mates, but under our experimental conditions has no detectable net effect on female fitness. These results broaden the functional scope of Acp29AB to include female reproductive schedule and suggest that some SFPs may evolve rapidly while either being effectively neutral or having context‐dependent effects on female fitness.

During epididymal transit, spermatozoa undergo crucial morphological, biochemical, and molecular modifications that enable the acquisition of motility, acrosomal remodeling, membrane reorganization, and chromatin stabilization, culminating in full maturation. This study investigated sperm motility, sperm head and acrosome remodeling, chromatin compaction (protamination), DNA integrity, and nuclear morphology in sperm collected from different epididymal regions (caput, corpus, cauda) and the vas deferens in three closely related mouse species exhibiting varying levels of sperm competition. Using microscopy, fluorescent staining (Hoechst 33342, chromomycin A3), sperm chromatin structure assay (SCSA), and nuclear morphology software, we characterized these parameters. Results demonstrated a gradual acquisition of total and progressive motility from the caput onwards and a shift toward a more compacted acrosome, especially between corpus and cauda. Minor species-specific variations in nuclear shape and dimensions were observed. Chromatin compaction and DNA integrity significantly increased, evidenced by decreased chromomycin A3 positive cells and reduced DNA fragmentation indices (tDFI and HDS). A correlation between protamine status and DNA fragmentation appeared when data from all species were pooled. M. musculus showed lower overall motility and a faster decline in loose acrosomes. M. spicilegus exhibited the most rapid sperm head compaction, whereas M. spretus had the highest sperm nuclear width and the lowest tDFI values. These findings reveal distinct changes in sperm maturation markers along the epididymis and suggest associations between these changes and sperm competition levels of these species. This enhances our understanding of sperm maturation mechanisms and may inform advances in reproductive technologies.

Abstract Sexual selection can be an engine of divergent evolution between closely related lineages, as a result of idiosyncratic coevolution of male and female reproductive traits. The possibility that this can contribute to speciation has ample support from comparative studies but very few experimental evolution studies have addressed the role of sexual selection in very early stages of divergent evolution. Here, we use experimental evolution to study divergent evolution between replicate lines of the seed beetle Acanthoscelides obtectus evolving under strong or weak sexual selection for >190 generations. We first confirm that the experimental regimes employed resulted in marked differences in the strength of sexual selection. We then indirectly assess the degree of divergent evolution of those male and female traits that affect postmating sexual selection, by crossing replicate lines. We find that lines evolving under strong sexual selection are more divergent in reproductive traits, as evidenced by a stronger male × female interaction for male sperm competition success. Finally, we assess the degree of divergent evolution in the expression of candidate genes for male seminal fluid proteins and female reproductive proteins. We find that lines evolving under strong sexual selection are more divergent in the expression of reproductive proteins, providing a possible causal mechanism contributing to the results seen in the reproductive phenotype. Our findings provide evidence for more divergent evolution of reproductive traits under stronger sexual selection, in line with the tenet that sexual selection may promote divergence even in the absence of environmental differences between populations.

Conspicuous sexual signals are frequently under selection from conflicting sources, such as natural versus sexual selection and pre-copulatory versus post-copulatory sexual selection, which may act in the same or different directions. The Pacific field cricket (Teleogryllus oceanicus) is undergoing rapid evolutionary trait loss: mutations that render males obligately silent (the "flatwing phenotype") have become established on several islands of Hawai'i. Females strongly discriminate against silent males, yet flatwings do gain matings. In this study, we take advantage of this natural system to understand how investment in ejaculate quality under high and low perceived sperm competition risk (manipulated using acoustic cues) differs between wild type males and flatwings, which obligately adopt alternative reproductive tactics (ARTs). We replicated our study in two islands with different flatwing frequencies because female mating rate and therefore sperm competition risk is likely higher in O'ahu than Kaua'i. We measured testes mass and gene expression for three seminal fluid proteins (SFPs) that affect paternity success, sperm viability, and female propensity to remate. Compared to Kaua'i males, O'ahu males showed higher residual testes mass and expression of ToSfp011, which increases male sperm viability and paternity success, and reduces mate searching behavior by females. We found no effect of immediate sperm competition risk or wing morph on any of the SFPs or testes mass. Differential SFP expression and residual testes mass in Hawaiian populations that likely differ in mating rate are compatible with the predictions of sperm competition theory.

The sperm tail is a modified motile cilium analogous to those found in tissues including the lung and brain. They have been evolutionarily sculpted to optimize motility and, therefore, fertility, through the dynamic and challenging environment of the female reproductive tract. Sperm tails are composed of three structurally distinct regions: the midpiece, the principal piece and the end piece. The most proximal region - the midpiece - is surrounded by a mitochondrial sheath, which has been proposed to provide structural integrity and ATP as fuel for sperm tail movement. Despite the main phases of mitochondrial sheath assembly being described, the specific biological mechanisms that underpin its formation and maturation remain poorly defined and, in many cases, unknown. Moreover, emerging evidence has highlighted that the precise contribution of the mitochondrial sheath to energy production in sperm has been misunderstood. ATP generation via glycolysis and mitochondrial respiration, previously believed to be physically uncoupled, engage in crosstalk to maximize sperm function, competition and overall fertility. Understanding these processes could not onlyprovide vital insights into the aetiology of male infertility and offer targets for contraceptive development but couldalso provide insights intomechanisms of relevance to other tissues in which mitochondrial dynamics is challenging to monitor.

Examples of convergent evolution, wherein distantly related organisms evolve similar traits, including behaviors, underscore the adaptive power of natural selection. In birds, obligate brood parasitism, and the associated loss of parental care behaviors, has evolved independently in seven different lineages, though little is known about the genetic basis of the complex suite of traits associated with this rare life history strategy. We generated genome assemblies for ten brood parasitic species plus eight species representatives of their parental/nesting outgroups. This includes nine long-read chromosome-level assemblies, with scaffold N50 sizes ranging from 38.1 to 72.6MB, and gene representation completeness measures > 97%. Leveraging this new catalog of avian genomes, we constructed clade-level alignments that reveal variation in chromosomal synteny, provide first-time or improved annotations of protein-coding and non-coding genes, and define cross-species ortholog reference sets. We also refine estimates for the timing of the seven independent origins of brood parasitism, ranging from recent events such as 1.6 to 4.5 million years ago in Molothrus cowbirds to much earlier origins over 30 million years ago in two of the three cuckoo lineages. These genomic resources lay the foundation for investigating the genetic and genomic underpinnings of brood parasitism, including the loss of parental care, shifts in mating systems, perhaps resulting in heightened sperm competition, elevated annual fecundity, improved spatial cognition related to nest-finding, and the diverse adaptations shaped by intense coevolution with host species.

Male moths rely on antennal olfactory sensilla to detect female-emitted sex pheromones during mate localization, a process critically mediated by pheromone-binding proteins (PBPs) that facilitate ligand transport to dendritic membrane-bound pheromone receptors. Intriguingly, a divergent PBP paralog (PBP4) in noctuid moths has been identified exhibiting predominant expression in the male reproductive system, though its functional significance remained elusive. In this study with Spodoptera exigua, we demonstrated that PBP4 is specifically expressed in male accessory glands (MAGs) and transferred to females during copulation. CRISPR-mediated PBP4 knockout (PBP4-/-) significantly reduced male reproductive success via impaired sperm competition, evidenced by diminished offspring sired. Transcriptomic and qPCR analyses revealed expressional correlation between PBP4 and the odorant receptor coreceptor (Orco), and similar sperm competition deficits were observed in Orco-/- males. Furthermore, both mutants exhibited compromised sperm motility and reduced sperm transfer from spermatophores to spermathecae. In vitro sperm motility assays showed that a specific agonist of Orco, VUAA1, robustly enhanced sperm motility in an Orco-dependent manner. Analyses of four additional moth species, including noctuids and non-noctuids, revealed a similar specific expression in the male reproductive tracts in all of them. Our findings unveil a noncanonical role for PBP4 in reproductive fitness and evolutionary conservation of the PBP-OR signaling pathway.

Seminal fluid proteins (Sfps) are essential for reproductive success and evolve fast on average, possibly driven by post-copulatory sexual selection (PCSS) originating from sperm competition and cryptic female choice. Counterintuitively, however, the coding region only in few Sfps evolves adaptively. Hence, additional genomic and functional factors must play a role in Sfp evolution independent of the protein coding region. To shed light on drivers of Sfp evolution we focus on those Sfps predominantly expressed in male accessory glands of Drosophila to examine their evolution in the tissue which produces the majority of Sfps. Unlike the testis, the accessory glands are known to develop normally in hybrids, allowing us to control for cellular environment differences arising during speciation. Here, we identify hotspots of rapid evolution in accessory gland protein genes (Acp) promoters, driven by base changes and insertions/deletions (indels). We further show that changes in promoter sequences are accompanied by gene expression divergence among closely related species. Using hybrids, we demonstrate that species-specific expression divergence is maintained for some Acps, while others exhibit dominance of one allele. These results indicate that regulatory evolution, rather than genome background variation, drives Acp expression changes and promotes their rapid evolution.

Post-copulatory sexual selection, comprised of sperm competition and cryptic female choice, is a powerful evolutionary force that can drive the rapid diversification of reproductive traits across taxa. In birds, the female reproductive tract provides the arena for post-copulatory sexual selection, yet we lack a comprehensive understanding of the female specific processes that shape the evolution of sexually selected traits. Here, we use a comparative approach to explore the relationships between female reproductive tract morphology, sperm competition intensity, and sperm traits across Galliformes. Accounting for phylogenetic and allometric relationships, we find that species with relatively larger testes for their body size—a proxy for intense sperm competition—have relatively longer vaginas, suggesting that important co-evolutionary dynamics exist between male and female reproductive physiology. Surprisingly, we find no link between sperm length and sperm storage tubule morphology, challenging existing predictions. Our findings suggest that the vagina has a significant but currently overlooked influence on post-copulatory processes and emphasizes the need to better integrate female morphology into models of sexual selection.

Sexual selection is a key driver of reproductive strategy evolution; however, its molecular mechanisms remain poorly understood. In the mouthbrooding Tanganyikan cichlid (Ophthalmotilapia ventralis), fertilization occurs in the female mouth cavity, where sperm competition and post-mating female choice arise because females collect sperm from multiple territorial males. Seminal plasma glycoprotein 120 (SPP120) is involved in sperm immobilization and aggregation, which may contribute to prolonged storage and use of sperm in the female buccal cavity. In this study, we examined how factors related to pre- and post-mating sexual selection affect sperm traits and SPP120 expression in O. ventralis. Field observations and physiological and molecular analyses showed positive correlations between sperm longevity of territorial males and encounter rate with floating males (ERFM) as a measure of sperm competition or bower (spawning site) density related to sperm competition and between SPP120 expression of territorial males and ERFM or courtship success as a measure of pre- and post-mating female mate choice. Furthermore, males with higher SPP120 expression levels achieved greater mating success. These findings highlight the complex interplay between sexual selection and molecular adaptation, providing new insights into the evolution of animal reproductive strategies.

Sexual cannibalism, a behavioral syndrome where one mating partner consumes the other before, during, or after copulation, is particularly widespread among spiders and often exemplifies sexual conflict. Female sexual cannibalism has driven the evolution of numerous male counter-adaptations. Here we review sexual cannibalism in spiders, evaluate five broad hypotheses explaining its evolution, and provide possible explanations for numerous male reproductive strategies associated with this behavior. These male strategies include mating with immature females, opportunistic mating with molting or feeding females, coercive mating, nuptial gifts, inducing female quiescence, thanatosis, mate binding, sperm transfer adjustments, catapulting, and remote copulation. We emphasize the importance of clearly defining these behaviors and advocate for greater experimental repeatability in future experimental and comparative research. The evolutionary dynamics of these strategies are discussed within the frameworks of sexual conflict, sexually antagonistic coevolution, sperm competition, and cryptic female choice. We call for future research to expand taxonomic sampling, standardize methodologies, integrate field-based observations/experiments, and quantify the costs and benefits for each sex. Such efforts are essential to contextualize sexual cannibalism within broader ecological and evolutionary paradigms.

The genitalia of Lepidoptera are complex structures that evolve rapidly and divergently. The endophallus of many lepidopterans is ornamented with elaborate sclerotized structures known as cornuti. In some species, the cornuti are deciduous and remain within the female genital tract after copulation; the function of these structures is virtually unknown. These structures are a peculiar potential type of secondary “socially transferred material” (the primary materials are spermatozoids, i.e., genetic material), because they probably influence the physiology and behaviour of receivers (i.e., females) but are not molecules that function as allohormones. Such influence could be achieved by acting as mating plugs or via mechanical stimulation of females. The most intriguing and bizarre deciduous cornuti are the so-called caltrop cornuti, star-shaped structures, composed of several rays radiating from a central mass. Despite the presence of caltrop cornuti in at least 400 species, there are no studies of their microscopic structure and mechanism of dislodgement and transference to the female. In this study, we describe in detail the general and microscopic structure of the caltrop cornuti and associated structures of the prominent moth Peridea anceps (Notodontidae). We provide quantitative data of the cornuti and, for the first time, we explain the processes of detachment and transference to the female genital tract; we also describe their distribution inside the female genitalia. We discuss the possibility that one of the functions of deciduous caltrop cornuti is protection against sperm competition, as well as their potential influence on other aspects of the behaviour and physiology of females via mechanical stimulation.

Inbreeding and the associated increase in homozygosity and potential accumulation of deleterious alleles may reduce fitness in a process known as inbreeding depression. Mechanisms to mitigate reproduction between close relatives, ranging from pre‐mating mate choice to post‐mating gamete selection, have evolved across taxa. In external fertilisers like Atlantic salmon (Salmo salar), where females have limited control over paternity, mechanisms of inbreeding avoidance can be expected to evolve at the gamete level.Philopatric Atlantic salmon may run the risk of breeding between relatives, particularly in small populations, and frequent escapes from aquaculture settings are augmenting the chances of adults from the same sibling cohort overlapping in the wild, raising potential ecological and sustainability concerns. Moreover, the presence of inbreeding avoidance mechanisms between full siblings in externally fertilising fish is currently untested.This study tested post‐mating inbreeding avoidance mechanisms in domesticated Atlantic salmon. In a paired breeding design, we compared sperm motility parameters in sibling and non‐sibling ovarian fluid, and assessed fertilisation and hatching success, growth rate and paternity in sperm competition trials between sibling and non‐sibling males.Sperm activated in ovarian fluid of sibling females showed lower values of motility‐related parameters and led to an average of 18% reduction in fertilisation rates in the resulting crosses. Furthermore, offspring from sibling crosses were smaller before the onset of sexual maturation. However, we found no difference in survival rates between sibling and non‐sibling cross offspring. Besides, when sperm from sibling and non‐sibling males were competing simultaneously for the same egg batch, we found no influence of this on paternity.Our findings reveal the presence of post‐mating inbreeding avoidance at the gamete level in Atlantic salmon, but its effects are limited in competitive scenarios.Our results have implications for salmonid conservation and aquaculture, where small natural or closed domestic strains may both display a degree of inbreeding. Mating between escaped domestic and wild salmonids could favour admixed over wild or feral crosses if an inbreeding avoidance mechanism is present; although this remains to be tested in more outbred crosses.

Examples of convergent evolution, wherein distantly related organisms evolve similar traits, including behaviors, underscore the adaptive power of natural selection. In birds, obligate brood parasitism, and the associated loss of parental care behaviors, has evolved independently in seven different lineages, though little is known about the genetic basis of the complex suite of traits associated with this rare life history strategy. We generated genome assemblies for ten brood parasitic species plus eight species representatives of their parental/nesting outgroups. This includes nine long-read chromosome-level assemblies, with scaffold N50 sizes ranging from 38.1 to 72.6 MB, and gene representation completeness measures >97%. Leveraging this new catalog of avian genomes, we constructed clade-level alignments that reveal variation in chromosomal synteny, provide first-time or improved annotations of protein-coding and non-coding genes, and define cross-species ortholog reference sets. We also refine estimates for the timing of the seven independent origins of brood parasitism, ranging from recent events such as 1.6 to 4.5 million years ago in Molothrus cowbirds to much earlier origins over 30 million years ago in two of the three cuckoo lineages. These genomic resources lay the foundation for investigating the genetic and genomic underpinnings of brood parasitism, including the loss of parental care, shifts in mating systems, perhaps resulting in heightened sperm competition, elevated annual fecundity, improved spatial cognition related to nest-finding, and the diverse adaptations shaped by intense coevolution with host species.

Abstract Mate guarding enables males to bias fertilization, increase their share of paternity, and thereby enhance reproductive success. When the risk of sperm competition is high, males may benefit from investing more in guarding behaviors. While some species physically restrain females during guarding, others use more passive tactics. Male Pacific field crickets (Teleogryllus oceanicus) sing after mating to entice females to stay, even though they cannot mate again immediately. Post-copulatory song effectively keeps females in proximity, prolongs spermatophore attachment, and ultimately enhances male reproductive success. We investigated whether cues about the risk of sperm competition determine male investment in post-copulatory song. Additionally, we studied whether hearing cricket calls either during rearing or immediately before mating modified the listeners' behavior. Males exposed to acoustic cues of male competitors during rearing or immediately before mating were not more likely to sing post-copulatory songs. However, among those males that did sing post-copulatory songs, those exposed to song during rearing had a greater latency to begin singing and overall spent less time singing post-copulation than males exposed to silence. These findings suggest that early-life social environments shape long-term mating strategies, while immediate cues have limited influence on post-copulatory mate guarding behavior.

Mate‐choice copying occurs when the choices of others influence an individual's mating preferences. While this behavior has been observed across various species, most research has focused on female copying behavior. However, male mate‐choice copying warrants independent attention due to the distinct benefits and costs it entails for males compared to females. Male mate‐choice copying may confer advantages, such as reducing the risk of costly mistakes by relying on the mate choices of others, conserving time and energy spent on mate searching, and increasing the likelihood of securing a high‐quality female mate. However, potential downsides include the risk of female rejection, intensified sperm competition, and the cost of missed opportunities. This review explores the scope of male mate‐choice copying, the conditions under which it occurs, and its associated benefits and costs. Additionally, it highlights the need for further research, particularly in species with high reproductive costs or those exhibiting last‐sperm precedence.

ABSTRACTReproductive barriers limit gene flow and drive population divergence. Sperm morphology plays an important role in reproductive barriers, as successful fertilization depends on how well sperm perform in the female environment. Specifically, sperm length must be adapted to fit the female reproductive tract and storage organs. We investigated sperm length in species and ecotypes of Littorina, a genus of promiscuous marine snails with internal fertilization. Various Littorina species have ecotypes adapted to different shoreline environments where reproductive traits like sperm length divergence might play a role in reinforcing these barriers. Due to their promiscuity, sperm competition likely plays a role in Littorina, and sperm length variation can give insights regarding sperm competition intensities. This study examined eusperm length in four species (L. fabalis, L. littorea, L. obtusata, L. saxatilis) and two different ecotypes in both L. fabalis and L. saxatilis. The ecotypes of both L. fabalis and L. saxatilis differed in eusperm lengths, indicating the potential for this trait to be involved in prezygotic reproductive barriers between ecotypes of these species. Among‐species differences in eusperm length variation were observed and may be a result of different sperm competition intensities.

Male reproductive success is determined by the interplay of female mate choice and male-male competition, often linked to dominance rank in social animals. Across taxa, elaborate ornaments, such as bright coloration or large antlers, often function as badges of status, signalling male competitive ability to rivals. In species where females mate with multiple males, post-mating sperm competition also plays an important role in male reproductive success and is associated with larger relative testes size. We investigate the relationship between morphological features and dominance rank in wild male white-faced capuchins. Using parallel-laser photogrammetry, we measured aspects of facial morphology, including facial width-to-height ratio, and testes size. We found that alpha males had significantly larger facial width-to-height ratios, wider faces and wider scrota than subordinate males. These results suggest that facial traits potentially function as badges of status in male white-faced capuchins and may play a role in pre-mating competition and/or mate choice, while differences in scrotal size reflect adaptations for post-mating competition. This study highlights the under-recognized role of facial trait evolution in sexual selection among relatively gracile yet highly visually oriented mammals and the potential variability of sexual traits in species characterized by strong reproductive skew among males.