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The study of polyandry has received increasing scientific attention with an emphasis on the fitness benefits and costs that females derive from mating with multiple males. There are still gaps in our understanding of how polyandry affects female fitness, however, as many previous studies compared the fitness outcomes of a single mating vs. 2 or 3 matings and did not separate the consequences of multiple mating from the costs of sexual harassment. We, therefore, conducted controlled mating trials with female fruit flies (Drosophila melanogaster) that could mate at either low (every 8 days), medium (every 4 days), or high (every other day) rates while controlling for exposure to harassment from males. We found that female lifetime fitness was highest under the high mating-rate followed by the medium mating-rate conditions. Moreover, we did not detect reductions in lifespan as a consequence of higher rates of polyandry. Our results demonstrate that even at realistically high rates, polyandry can lead to net fitness benefits for females, which can have major implications for sexual selection. Specifically, we discuss the significance of our findings as they relate to competition and the evolution of secondary sex characteristics in females, and sperm competition among males. [ABSTRACT FROM AUTHOR]

The intensity and direction of sexual selection are intricately linked to the social and ecological context. Both operational sex ratios (OSRs) and population densities can affect the ability of males to monopolize resources and mates, and thus the form and intensity of sexual selection on them. Here, we studied how the mating system of the promiscuous and strongly sexually dimorphic fruit fly Drosophila prolongata responds to changes in the OSR and population density. We recorded groups of flies over five days and quantified territory occupancy, mating success (MS) and competitive fertilization success. Although sexual selection was stronger under male-biased than even OSRs but unrelated to density, realized selection on morphological traits was higher under even OSRs and increased with density. Larger and more territorial males achieved both higher MS and competitive fertilization success, but only under even OSRs. Our combined results also support a shift in the mating system from territorial contest competition to scramble competition under male-biased OSRs and potentially at low density, where there was no clear contribution of the measured traits to reproductive success. Our study emphasizes the limitations of traditional selection metrics and the role of the socio-ecological context in predicting adaptation to a changing environment. [ABSTRACT FROM AUTHOR]

Promiscuous females reduce male reproductive control. Males can attempt to monopolise access to these females, but distractions and sneaky rivals mean extra copulations cannot always be blocked. By mating first, males can obtain a headstart in sperm competition, but this may be negated by sperm storage and cryptic female choice mechanisms. We carry out an indirect rare test of an early mating advantage in a population of free-living wild animals. Using Bayesian GLMM analysis of a long-term life history database spanning 17 years, we show that banded mongoose males who interacted with females in earlier days of oestrus had a higher chance of siring their offspring compared with later rivals. An early mating advantage would intensify initial male-male competition and hence selection for male choice, as any initial mistake identifying preferred mating partners could see paternity lost to rivals. [ABSTRACT FROM AUTHOR]

Sperm are traditionally viewed as transcriptionally and translationally silent cells. However, observations that components of the cellular machinery of gene expression are maintained in ejaculated sperm are increasingly cited as challenges to this fundamental assumption. Here, we critically evaluate these arguments and present three lines of evidence from both model and non-model systems that collectively raise the question of whether ejaculated sperm may be capable of active gene expression. First, and critical for arguments surrounding the possibility of differential gene expression, we review recent evidence that spermatozoa may retain the capacity to transcribe and translate their genomes. Second, we highlight how sperm cells can exhibit differential transcript quantities across different post-ejaculation environments. Third, we ask whether the accumulating evidence of remarkable phenotypic plasticity in post-ejaculatory sperm phenotypes could be mechanistically underpinned by changes in sperm gene expression. While these lines of evidence are indirect and do not definitively show transcription of sperm genomes, we highlight how emerging technologies may enable us to test this hypothesis explicitly. Our review advocates for progress in this field and highlights several important evolutionary, ecological and practical implications that will probably transcend disciplines to the clinical and applied reproductive sectors. [ABSTRACT FROM AUTHOR]

Sperm competition is known to favor the evolution of male traits that confer an advantage in gaining fertilizations when females mate multiply. Ejaculate production can be costly and the strategic allocation of sperm in relation to the sperm competition environment is a taxonomically widespread phenomenon. However, variation among males in their ability to adjust ejaculate allocation has rarely been explored. Here, we manipulated the phenotypic condition of male seed beetles, Callosobruchus maculatus , via larval diet quality and measured ejaculate allocation across varying levels of sperm competition manipulated using olfactory cues. Furthermore, we asked how strategic ejaculation was impacted by previous ejaculation. We found no variation in ejaculate allocation in response to experimentally manipulated cues to sperm competition. Ejaculate allocation was reduced by a male's previous mating history but was unaffected by the larval diets on which males were reared. We suggest that either male seed beetles are unable to adjust ejaculate size to the immediate competitive environment, or that sperm displacement strategies employed by males favor maximal investment at all mating events, especially when unmated females are infrequently encountered. As our study is one of few to examine condition dependence in strategic ejaculation, emphasis should be placed on future studies investigating this possibility across a wider range of taxa and animal mating systems. [ABSTRACT FROM AUTHOR]

Previous research suggests that human males, like males of many mammalian and avian species, adjust their ejaculate quality in accordance with sperm competition risk. Men who spend less time with their regular female partner since the couple's last copulation produce ejaculates with more sperm at the couple's next copulation (Baker & Bellis, 1993). We conducted a conceptual replication of this research to investigate whether sperm competition risk predicts ejaculate adjustment in human males using additional measures of sperm competition risk (e.g., perceptions of partner infidelity, presence of potential sexual rivals) and updated laser-optic semen analysis technology. We collected data from 34 heterosexual couples (age range 18–32 years) from a university population who completed self-report surveys on their relationship dynamics and provided six ejaculate samples (three copulatory and three masturbatory) across a 45-day period. Time spent together since the couple's last copulation was not significantly associated with ejaculate quality. However, sperm concentration for copulatory ejaculates was higher for men who perceived more potential sexual rivals. Discussion situates the current results within the literature on human sperm competition and suggests several directions for future research. [ABSTRACT FROM AUTHOR]

Extra-pair paternity is common among socially monogamous bird species and considered an important driver of post-copulatory sexual selection on ejaculate traits including sperm traits. Patterns of extra-pair paternity and sperm size both show substantial variation among populations, yet we know little about the expression of these key reproductive traits at high latitudes. Here we report patterns of extra-pair paternity and describe variation in sperm dimensions in a Norwegian population of the socially monogamous Great Tit (Parus major) breeding beyond the polar circle at 69° northern latitude. Across six study years, we detected extra-pair paternity in 19.2% of 26 broods, and on average 4.7% of nestlings per brood were extra-pair offspring. As expected from results of previous intraspecific analyses of latitudinal variation in extra-pair paternity rates, the observed rate of extra-pair offspring was low in comparison to published estimates from more southern Great Tit populations (range: 2.9 − 20.4%). Our results therefore support a pattern of decreasing levels of extra-pair paternity with increasing latitude in this species also for extremely high latitudes. Overall mean sperm total length amounted to 97.5 ± 0.6 (SE) μm and 30.6% of the total phenotypic variation in sperm total length was explained by differences among sperm samples. The among-sample coefficient of variation in mean sperm total length per sample was 1.93%. Using previous comparative work as a yardstick, this value is substantially lower than expected for the observed frequency of 4.7% extra-pair offspring. [ABSTRACT FROM AUTHOR]

Sperm morphology varies considerably among species. Sperm traits may contribute to speciation if they diverge fast in allopatry and cause conspecific sperm precedence upon secondary contact. However, their role in driving prezygotic isolation has been poorly investigated. Here we test the hypothesis that, early in the speciation process, female promiscuity promotes a reduction in overlap in sperm length distributions among songbird populations. We assembled a data set of 20 pairs of populations with known sperm length distributions, a published estimate of divergence time, and an index of female promiscuity derived from extrapair paternity rates or relative testis size. We found that sperm length distributions diverged more rapidly in more promiscuous species. Faster divergence between sperm length distributions was caused by the lower variance in the trait in more promiscuous species, and not by faster divergence of the mean sperm lengths. The reduced variance is presumably due to stronger stabilizing selection on sperm length mediated by sperm competition. If divergent sperm length optima in allopatry causes conspecific sperm precedence in sympatry, which remains to be shown empirically, female promiscuity may promote prezygotic isolation, and rapid speciation in songbirds. [ABSTRACT FROM AUTHOR]

It remains unclear how variation in the intensity of sperm competition shapes phenotypic and molecular evolution across clades. Mice and rats in the subfamily Murinae are a rapid radiation exhibiting incredible diversity in sperm morphology and production. We combined phenotypic and genomic data to perform phylogenetic comparisons of male reproductive traits and genes across 78 murine species. We identified several shifts towards smaller relative testes mass (RTM), presumably reflecting reduced sperm competition. Several sperm traits were associated with RTM, suggesting that mating system evolution selects for convergent suites of traits related to sperm competitive ability. We predicted that sperm competition would also drive more rapid molecular divergence in species with large testes. Contrary to this, we found that many spermatogenesis genes evolved more rapidly in species with smaller RTM due to relaxed purifying selection. While some reproductive genes evolved rapidly under recurrent positive selection, relaxed selection played a greater role in underlying rapid evolution in small testes species. Our work demonstrates that postcopulatory sexual selection can impose strong purifying selection shaping the evolution of male reproduction and that broad patterns of molecular evolution may help identify genes that contribute to male fertility. [ABSTRACT FROM AUTHOR]

The article discusses the use and definitions of the terms "arena," "lek," and "court" in describing avian courtship sites. It argues that "arena" is inaccurate and inappropriate, while "lek" is the more appropriate term. The author reviews historical and contemporary literature to clarify the distinctions between these terms and emphasizes the importance of using accurate terminology in ornithology. The article provides definitions for "lek," "dispersed lek," "lekking," and "court," aiming to eliminate confusion and promote clarity in describing avian courtship behavior. [Extracted from the article]

Attractiveness is not solely determined by a single sexual trait but rather by a combination of traits. Because the response of the chooser is based on the combination of sexual traits in the courter, variation in the chooser's responses that are attributable to the opposite-sex courter genotypes (i.e. the indirect genetic effects [IGEs] on chooser response) can reflect genetic variation in overall attractiveness. This genetic variation can be associated with the genetic basis of other traits in both the chooser and the courter. Investigating this complex genetic architecture, including IGEs, can enhance our understanding of the evolution of mate choice. In the present study on the field cricket Gryllus bimaculatus , we estimated (1) genetic variation in overall attractiveness and (2) genetic correlations between overall attractiveness and other pre- and postcopulatory traits (e.g. male latency to sing, female latency to mount, male guarding intensity, male and female body mass, male mandible size, and testis size) within and between sexes. We revealed a genetic basis for attractiveness in both males and females. Furthermore, a genetic variance associated with female attractiveness was correlated with a genetic variance underlying larger male testes. Our findings imply that males that mate with attractive females can produce offspring that are successful in terms of precopulatory sexual selection (daughters who are attractive) and postcopulatory sexual selection (sons with an advantage in sperm competition), potentially leading to runaway sexual selection. Our study exemplifies how the incorporation of the IGE framework provides novel insights into the evolution of mate choice. [ABSTRACT FROM AUTHOR]

Simple Summary: In this study, we explored how the reproductive biology of scorpion males changes over the reproductive season, particularly focusing on the quality and quantity of sperm. By comparing early- and late-season males, we found that testis size, sperm number, and sperm viability were higher at the beginning of the season but declined with age. Interestingly, even when males were isolated without mating opportunities, they still maintain sperm quality over time, suggesting potential preserving despite senescence. We also found that males in better physical condition produced more sperm but experienced a greater decline in sperm health as they aged, likely due to the energy demands of reproduction. These findings reveal the natural challenges male scorpions face as they age, highlighting the complex balance between reproduction and survival. Understanding these patterns is valuable as it provides insight into the broader issues of aging, reproductive health, and energy allocation in animals, which may help inform conservation efforts and may promote awareness about the biological effects of senescence in wildlife. Seasonal reproductive dynamics and senescence have profound impacts on male fertility, yet these processes remain understudied in scorpions. This study investigates how reproductive parameters—such as testicular mass, sperm quantity, and viability—change over the course of the reproductive season in Urophonius achalensis males. We found that early-season males exhibited higher sperm quality and testicular mass compared to their older counterparts, suggesting that senescence, rather than reproductive effort, drives the decline in sperm viability. Interestingly, isolated males accumulated more sperm without a reduction in viability, highlighting potential mechanisms that preserve sperm quality despite senescence. Body condition also played a key role, with males in better condition showing higher sperm counts but facing a sharper decline in sperm viability as the season progressed, suggesting trade-offs between early reproductive success and later-life reproductive costs. Our findings offer novel insights into the reproductive strategies of scorpions, emphasizing the interplay between senescence, environmental stressors, and reproductive investment. This work provides new insights into the reproductive biology of scorpions, with broader implications for understanding the role of senescence and mating systems in shaping reproductive strategies. [ABSTRACT FROM AUTHOR]

Sexual selection has been a popular subject within evolutionary biology because of its central role in explaining odd and counterintuitive traits observed in nature. Consequently, the literature associated with this field of study became vast. Meta‐analytical studies attempting to draw inferences from this literature have now accumulated, varying in scope and quality, thus calling for a synthesis of these syntheses. We conducted a systematic literature search to create a systematic map with a report appraisal of meta‐analyses on topics associated with sexual selection, aiming to identify the conceptual and methodological gaps in this secondary literature. We also conducted bibliometric analyses to explore whether these gaps are associated with the gender and origin of the authors of these meta‐analyses. We included 152 meta‐analytical studies in our systematic map. We found that most meta‐analyses focused on males and on certain animal groups (e.g. birds), indicating severe sex and taxonomic biases. The topics in these studies varied greatly, from proximate (e.g. relationship of ornaments with other traits) to ultimate questions (e.g. formal estimates of sexual selection strength), although the former were more common. We also observed several common methodological issues in these studies, such as lack of detailed information regarding searches, screening, and analyses, which ultimately impairs the reliability of many of these meta‐analyses. In addition, most of the meta‐analyses' authors were men affiliated to institutions from developed countries, pointing to both gender and geographical authorship biases. Most importantly, we found that certain authorship aspects were associated with conceptual and methodological issues in meta‐analytical studies. Many of our findings might simply reflect patterns in the current state of the primary literature and academia, suggesting that our study can serve as an indicator of issues within the field of sexual selection at large. Based on our findings, we provide both conceptual and analytical recommendations to improve future studies in the field of sexual selection. [ABSTRACT FROM AUTHOR]

Socially induced plasticity in reproductive effort is a widely documented phenomenon. However, few empirical studies have examined how male and female plastic responses to the social environment might interact in determining fitness outcomes. In field crickets, Teleogryllus oceanicus , males respond to rival songs by increasing expenditure on seminal fluid proteins that enhance competitive fertilization success at the cost of reduced embryo survival. It remains unknown whether plastic responses in females could moderate the effects of male competitiveness on offspring performance. Here, we used a fully factorial design to explore the interacting effects on fitness of male and female plasticity to the sociosexual environment. We found that female crickets exposed to male songs increased the number of eggs produced during early life reproduction, which came at the cost of reduced offspring size. There was evidence, albeit weak, that interacting effects of male and female sociosexual environments contributed to variation in the hatching success of eggs laid by females. Lifetime offspring production was unaffected by the sociosexual environments to which upstream male and female plastic responses were made. Our data offer a rare test of the theoretical expectation that male and female plasticities should interact in their effects on female fitness. [ABSTRACT FROM AUTHOR]

Despite rapid evolution across eutherian mammals, the X-linked MIR-506 family miRNAs are located in a region flanked by two highly conserved protein-coding genes (SLITRK2 and FMR1) on the X chromosome. Intriguingly, these miRNAs are predominantly expressed in the testis, suggesting a potential role in spermatogenesis and male fertility. Here, we report that the X-linked MIR-506 family miRNAs were derived from the MER91C DNA transposons. Selective inactivation of individual miRNAs or clusters caused no discernible defects, but simultaneous ablation of five clusters containing 19 members of the MIR-506 family led to reduced male fertility in mice. Despite normal sperm counts, motility, and morphology, the KO sperm were less competitive than wild-type sperm when subjected to a polyandrous mating scheme. Transcriptomic and bioinformatic analyses revealed that these X-linked MIR-506 family miRNAs, in addition to targeting a set of conserved genes, have more targets that are critical for spermatogenesis and embryonic development during evolution. Our data suggest that the MIR-506 family miRNAs function to enhance sperm competitiveness and reproductive fitness of the male by finetuning gene expression during spermatogenesis.

Objective: To support the declining wild population of Delta Smelt, a conservation hatchery has expanded its mission from maintaining a backup population as insurance against extinction to also producing fish for release into the wild. The substantially higher production demands require a balance between producing large numbers of fish while adhering to conservation genetic principles that maximize retention of effective population size (Ne) and thus overall diversity. Methods: We performed spawning experiments at the hatchery to evaluate the genetic consequences of two spawning strategies: (1) a pooled strategy where we fertilized premixed eggs from three dams with premixed milt from three sires and (2) a partial-factorial strategy where eggs from three dams were mixed and then apportioned among three containers, each container then receiving milt from one sire. We used genetic parentage analysis of larval offspring to determine the reproductive success of spawners in 10 replicate crosses of each strategy. Result: The contributions of parents to offspring were more even in partial-factorial crosses and consequently resulted in higher Ne (average Ne = 5.50 ± 0.38; expected Ne = 6.0), suggesting its potential for maintaining genetic diversity over time. In contrast, our pooled spawning experiment produced lower and more variable Ne values (average Ne = 3.86 ± 1.30), demonstrating that this more efficient method of production entails high costs in terms of long-term genetic management. Treating our experiments as hypothetical pools of fish for release, we combined the Ne values for pooled or partial-factorial crosses to calculate the effective size of a release population (NeR). Unequal family sizes reduced NeR for our pooled experiment to half of the expected value, whereas the partial-factorial experiment NeR was 88% of the expected value. Conclusion: We discuss the benefits and risks of each method and how these can be considered when designing a spawning strategy for Delta Smelt supplementation.

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

The article discusses the impact of population size, structure, fertilization success, and propagule dimorphism on sex allocation in simultaneous hermaphrodites, focusing on plant reproduction. The authors present a mathematical model that challenges classical sex allocation theory by showing that population size, pollen mortality, and fertilization success can influence sex allocation. The study reanalyzes the model and confirms the classical result of equal sex allocation under panmixia. The research highlights the importance of considering population structure and dispersal rates in understanding sex allocation evolution. [Extracted from the article]

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

Simple Summary: Ground beetle (Carabidae) spermatozoa are often aggregated in bundles of different sizes and are covered by a secretory material produced by the deferent duct epithelium. These secretions can have different shapes being either similar to a cap or to a rod (spermatostyle). Through a detailed study of the different regions of the male reproductive systems, we were able to describe the origin of this protective structure. We have obtained evidence that the secretions from the duct epithelium have initially an irregular shape, with the spermatozoa present in the duct lumen adhering to the structure with their heads on one side only. Later on, along their maturation, these structures bend, taking a cap shape. Hence, this process of secretion and successive evolution of the structures is very similar to that occurring in the spermatostyles. In conclusion, we obtained clear evidence that the two models of the sperm bundle protection share the same origin and thus they can be considered as homologous. The males of Carabus lefebvrei produce sperm bundles of quite variable size as a consequence of a sexual selection via sperm competition. The ultrastructural features of spermatogenesis of the species and the sequence of events leading to sperm bundle formation along the deferent duct lumen revealed the origin and evolution of the apical structure protecting the sperm bundles. Elongated layers of the electron-dense material of variable size and thickness are visible over the microvilli of the distal deferent duct epithelium. They likely correspond to sections through different levels of discoidal secretions. Then, the sperm present in the duct lumen attach to one side of such elongated secreted structures. Later on, these structures bent to take a cap shape and increase their size and thickness by apposition of additional secretions produced by the proximal deferent duct epithelium. These results reconcile the different opinions about the formation of the structures called the cap and the rod (spermatostyle). In our work, we in fact obtained evidence that both these structures have the same origin, even though at the end of their formation they exhibit a different appearance. The reported results indicate that, differently from the spermatostyle, in the initial stages of cap formation, the sperm adhere only to one side of the cap rather than around the whole structure, as it occurs instead along the spermatostyle rod. Under this aspect, the cap structure is similar to the protection present in the sperm of some whirligig beetle. [ABSTRACT FROM AUTHOR]

Our understanding of sexual selection is advancing with new technologies that tag individuals or their sperm, revealing how females use post‐copulatory processes to discriminate between competing mates. Many tagging methods have been devised primarily for model insect organisms like Drosophila or Gryllidae. Developing such novel methods, however, is expensive and requires intensive investment. In this experiment, we trial the use of Rhodamine B (RhB) and Rhodamine 110 (Rh110) in a small arachnid, the bulb mite Rhizoglyphus echinopus, for pre‐ and post‐copulatory observations as it is a relatively inexpensive and simple way to tag individuals and their ejaculate proteins. First, we tested whether RhB and Rh110 applied to food can be used as a tagging method to track and distinguish between individuals. Second, we explored whether Rhodamine applied in this way can be used to track sperm transfer. We found that both tagging probes worked well in tagging individuals and that we were able to distinguish between individuals using both LED and fluorescent microscopy. We also found that Rhodamine degraded rapidly in the animals, likely due to their fast metabolism. Due to the rapid degradation, we observed variable results in the sperm transfer trials. We suggest multiple uses for Rhodamine and highlight other invertebrates where this method may come into use for the study of sexual selection. [ABSTRACT FROM AUTHOR]

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

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

Hybridisation is a complex process that begins with mating. Females have more to lose with each hybrid fertilisation than males, so they should avoid it. Even if females choose con‐specific males as preferred mates, they often cannot control which additional males release sperm during spawning. Polyandry is ubiquitous and may result in hetero‐specific sperm competition between males of different species. In such cases, cryptic female choice (the ability to bias paternity towards certain males under sperm competition) is the last line of defence to prevent hybridisation of her eggs and is highly adaptive if it enables con‐specific sperm preference. Such seems to be the case with the hybridisation of Atlantic salmon (Salmo salar) and brown trout (S. trutta) in their native Europe. Under hetero‐specific sperm competition, hybrid fertilisations in these fish are reported to be reduced via ovarian fluid‐mediated cryptic female choice. It is not known, however, whether the strength of this mechanism is dependent on reinforcement and thus, the historical sympatry/allopatry of hybridising populations. Brown trout are one of the world's worst invasive species. Ecological impacts arise through competition with other species (e.g. Galaxids in the southern hemisphere, Oncorhynchus in western North America). Eastern North America contains native salmonids that evolved in the absence of brown trout but have gametes that are compatible. The 140 ‐year‐old brown trout invasion of Newfoundland is ground zero to study these potential interactions. Their relatively low spread rate across the island may be the result of inherent poor productivity, but data suggest it could also be a function of hybridisation with native Atlantic salmon and brook char (Salvelinus fontinalis). [ABSTRACT FROM AUTHOR]

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

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

Simple Summary: For the sterile insect technique to be successful, sterile male mosquitoes need to outcompete fertile males and mate with wild females. Some female insects, however, have been shown to be able to select for "better sperm" to secure high-quality offspring. This study used stable isotopes to mark the sperm of sterile and fertile males to find any evidence of female tiger mosquitoes selecting the fertile sperm over the sterile one when mated by both types of males. Although this study does not prove that a complex mechanism of sperm selection does not occur, we were not able to find any evidence that double-mated Aedes albopictus females favor fertile sperm for egg fertilization. The key to success in the application of the sterile insect technique (SIT) relies on the ability of released, sterile males to outcompete their fertile wild male counterparts to mate with wild females. However, many insect species exhibit multiple-mating behavior, which can be a way for females to select paternity for their progeny. This study aims to recognize the consequences of potential double-matings during an SIT program and to detect any evidence of sperm selection favoring sperm from fertile mates. This report provides a descriptive analysis of the storage and use of sperm by female Aedes albopictus. Stable isotopes were used to mark the sperm of fertile and sterile males. Mated females were allowed to oviposit before dissecting the spermathecae to link the presence of each type of sperm to the sterility of the eggs laid. It was found that sperm in females inseminated by both males was distributed in the three spermathecae with no obvious pattern, mostly mixed but also separately, and no evidence of any mechanism for sperm selection, sperm precedence, or sperm competition in Ae. albopictus females could be found. The fact that only a few double-mated females were double-inseminated and could also produce semi-sterile eggs, together with the finding that the sperm of sterile males appeared to be no less viable than that of fertile males, is an encouraging outcome for SIT approaches. [ABSTRACT FROM AUTHOR]

Theoretically, males should increase their ejaculate expenditure when the probability of sperm competition occurring (or risk) is high but decrease ejaculate expenditure as the number of competing ejaculates (or intensity) increases. Here we examine whether male decorated crickets (Gryllodes sigillatus) use cuticular hydrocarbons (CHCs) transferred to females by rival males at mating to assess the risk and intensity of sperm competition and adjust their ejaculate accordingly. Unmated females and those perfumed with CHCs extracted from one, three, or five males could be distinguished chemically, providing a reliable cue of the risk and intensity of sperm competition. In agreement with theory, males mating with these females increased sperm number with the risk of sperm competition and decreased sperm number with the intensity of sperm competition. Similarly, as the risk of sperm competition increased, males produced a larger and more attractive spermatophylax (an important non-sperm component of the ejaculate) but these traits did not vary with the intensity of sperm competition. Our results therefore demonstrate that both sperm and non-sperm components of the male ejaculate respond to the risk and intensity of sperm competition in different ways and that CHCs provide males with an important cue to strategically tailor their ejaculate. [ABSTRACT FROM AUTHOR]

One yet unresolved question in the study of mating system evolution is the occurrence of mating failure, when individuals go through their lives without successfully mating. This includes the failure to produce offspring even following copulation, for instance due to insemination or fertilisation failure. Copulations are costly in a variety of ways, but also a fundamental route to fitness in sexual species, and so we should expect that engaging in copulations that generate no offspring should be strongly selected against. Nonetheless, it has become apparent that mating failure is quite common in nature. Here we consider post‐copulatory sexual selection in Lygaeus simulans seed bugs to test the hypothesis that the high levels of mating failure found in this species (approximately 40%–60%) are caused by cryptic male choice (i.e. males choosing not to inseminate a female during copulation). In our first experiment, we found that mating failure depended on female size, but not male size, with smaller females experiencing mating failure more frequently. Mechanistically this is likely to be due to copulation duration, as shorter copulations were more likely to lead to mating failure. Likewise, copulations with smaller females were shorter. In our second and third experiments, rates of mating failure decreased when pairs were allowed to repeatedly interact with the same partner over longer durations (hours through to days), implying that mating failure is not primarily caused by infertility or chronic mechanical failure. Instead, our results strongly suggest cryptic male choice as the cause of mating failure in this species. [ABSTRACT FROM AUTHOR]

The Darwin–Bateman paradigm predicts that females enhance their fitness by being choosy and mating with high‐quality males, while males should compete to mate with as many females as possible. In many species, males enhance their fitness by defending females and/or resources used by females. That is, males directly defend access to mating opportunities. However, paternity analyses have repeatedly shown that females in most species mate polyandrously, which contradicts traditional expectations that male defensive behaviours lead to monandry. Here, in an extensive meta‐analysis, encompassing 109 species and 1026 effect sizes from across the animal kingdom, we tested if the occurrence of defensive behaviours modulates sexual selection on females and males. If so, we can illuminate the extent to which males really succeed in defending access to mating and fertilisation opportunities. We used four different indices of the opportunity for sexual selection that comprise pre‐mating and/or post‐mating episodes of selection. We found, for both sexes, that the occurrence of defensive behaviours does not modulate the potential strength of sexual selection. This implies that male defensive behaviours do not predict the true intensity of sexual selection. While the most extreme levels of sexual selection on males are in species with male defensive behaviours, which indicates that males do sometimes succeed in restricting females' re‐mating ability (e.g. elephant seals, Mirounga leonina), estimates of the opportunity for sexual selection vary greatly across species, regardless of whether or not defensive behaviours occur. Indeed, widespread polyandry shows that females are usually not restricted by male defensive behaviours. In addition, our results indicate that post‐mating episodes of selection, such as cryptic female choice and sperm competition, might be important factors modulating the opportunity for sexual selection. We discuss: (i) why male defensive behaviours fail to lower the opportunity for sexual selection among females or fail to elevate it for males; (ii) how post‐mating events might influence sexual selection; and (iii) the role of females as active participants in sexual selection. We also highlight that inadequate data reporting in the literature prevented us from extracting effect sizes from many studies that had presumably collected the relevant data. [ABSTRACT FROM AUTHOR]

Animals can adjust their consumption of different nutrients to adaptively match their current or expected physiological state. Changes in diet preference can arise from social and sexual experience. For example, in female Drosophila melanogaster fruit flies, a single mating triggers a behavioural switch in diet choice towards increased protein intake and total food consumption, which supports offspring production. In contrast, male diet choice appears to be unaffected by a single mating. However, one mating may not fully capture the impact of mating on male feeding behaviour. Males can often mate multiply in natural settings, and the costs of ejaculate production and energetic courtship may be cumulative, such that males might experience increased nutritional demands only after multiple matings. In this study we tested this prediction by measuring the effect of multiple matings on the diet choice of male D. melanogaster fruit flies. Males were assigned to one of three mating treatments, unmated, mated once or mated five times consecutively, and then allowed to feed freely on chemically defined diets of protein and carbohydrate. In contrast to the prediction, we found that males that mated five times did not alter the amount of food, or the proportion of protein and carbohydrate consumed, when compared with unmated or once-mated males. This absence of a feeding response occurred despite substantial ejaculate depletion from multiple matings: males sired fewer offspring in each consecutive mating. These results reveal a lack of plasticity in male feeding behaviour according to mating status, despite substantial potential physiological costs, and highlight the remarkably distinct nutritional ecologies of males versus females. • Female fruit flies show altered diet preference following mating. • However, dietary responses to mating in males are largely unknown. • We tested the impact of realistic mating rates on male fruit fly diet choice. • Males do not alter food intake to recoup depleted ejaculate, despite fertility loss. • These results highlight key sex differences in diet choice following mating. [ABSTRACT FROM AUTHOR]

The karyotype of an organism is the set of gross features that characterize the way the genome is packaged into separate chromosomes. It has been known for decades that different taxonomic groups often have distinct karyotypic features, but whether selective forces act to maintain these differences over evolutionary timescales is an open question. In this paper we analyze a database of karyotype features and sperm head morphology in 103 mammal species with spatulate sperm heads and 90 sauropsid species (birds and non-avian reptiles) with vermiform heads. We find that mammal species with a larger head area have more chromosomes, while sauropsid species with longer heads have a wider range of chromosome lengths. These results remain significant after controlling for genome size, so sperm head morphology is the relevant variable. This suggest that post-copulatory sexual selection, by acting on sperm head shape, can influence genome architecture. [ABSTRACT FROM AUTHOR]

Experimental research and theoretical models question the Darwin-Bateman paradigm that male reproductive success is just limited by the number of mates. Males have evolved tactics to tailor ejaculates among their mates to maximise fitness. Males are expected to be choosy and to bias ejaculate investment depending on the perceived quality of females (cryptic male choice) and/or the reproductive social context. We investigated ejaculate allocation strategy in Lobesia botrana, a mostly monandrous moth, depending on male size, female size, and their interaction, the latter effect being usually overlooked in most studies. The explained variables were absolute ejaculate size (spermatophore volume) and relative ejaculate size (ejaculate size to lifetime ejaculate expenditure ratio). Absolute ejaculate allocation analysis showed that: (1) ejaculate expenditure increases with male size; (2) males tailor greater ejaculates to larger than smaller females; and (3) there was no interaction between male size and female size, so small and large males tailored equivalent increases in ejaculate volume per female weight unit. Quite differently, relative ejaculate allocation analysis showed that: (1) small males invest comparatively more than large males in females of similar size; and (2) there was an interaction between female size and male size, so small males invest comparatively more than large males when mated with large females. Results are discussed in the framework of strategic ejaculate allocation from an evolutionary perspective, as ecological variables, including the current climate change scenario, may promote coexistence in the field of quite different-sized adults in this moth species. Significance statement: Available evidence supports that insects and other animals, including humans, exhibit strategic ejaculate allocation, which is shaped by an array of factors related to mate quality and reproductive social context. Among them, female size is especially important, as it positively correlates with fecundity and thereby largely regulates male fitness returns. We studied the ejaculate allocation pattern in the European grapevine moth, a usually monandrous species. We show that, in addition to female size, male size and male-by-female size interaction are critical drivers of ejaculate allocation. However, the interpretation of the results must be done carefully, as they may differ substantially depending on whether male investment is measured in absolute or relative terms. [ABSTRACT FROM AUTHOR]

Males often strategically adjust the number of available sperm based on the social context (i.e. sperm priming response), but it remains unclear how environmental and genetic factors shape this adjustment. In freshwater ecosystems, high ambient temperatures often lead to isolated pools of hotter water in which inbreeding occurs. Higher water temperatures and inbreeding can impair fish development, potentially disrupting sperm production. We used guppies (Poecilia reticulata) to investigate how developmental temperature (26 °C, 30 °C) and male inbreeding status (inbred, outbred) influence their sperm priming response. We also tested if sperm priming was affected by whether the female was a relative (sister) and whether she was inbred or outbred. There was no effect of rearing temperature; male inbreeding status alone determined the number of available sperm in response to female presence, her inbreeding status, and her relatedness. Inbred males produced significantly more sperm in the presence of an unrelated, outbred female than when no female was present. Conversely, outbred males did not alter the number of sperm available in response to female presence or relatedness. Moreover, inbred males produced marginally more sperm when exposed to an unrelated female that was outbred rather than inbred, but there was no difference when exposed to an inbred female that was unrelated versus related. Together, a sperm priming response was only observed in inbred males when exposed to an outbred female. Outbred females in our study were larger than inbred females, suggesting that inbred males strategically allocated ejaculate resources toward females in better condition. [ABSTRACT FROM AUTHOR]

Male–male contests for access to females or breeding resources are critical in determining male reproductive success. Larger males and those with more effective weaponry are more likely to win fights. However, even after controlling for such predictors of fighting ability, studies have reported a winner–loser effect: previous winners are more likely to win subsequent contests, while losers often suffer repeated defeats. While the effect of winning–losing is well-documented for the outcome of future fights, its effect on other behaviors (e.g. mating) remains poorly investigated. Here, we test whether a winning versus losing experience influenced subsequent behaviors of male mosquitofish (Gambusia holbrooki) toward rivals and potential mates. We housed focal males with either a smaller or larger opponent for 24 h to manipulate their fighting experience to become winners or losers, respectively. The focal males then underwent tests that required them to enter and swim through a narrow corridor to reach females, bypassing a cylinder that contained either a larger rival male (competitive scenario), a juvenile or was empty (non-competitive scenarios). The tests were repeated after 1 wk. Winners were more likely to leave the start area and to reach the females, but only when a larger rival was presented, indicating higher levels of risk-taking behavior in aggressive interactions. This winner–loser effect persisted for at least 1 wk. We suggest that male mosquitofish adjust their assessment of their own and/or their rival's fighting ability following contests in ways whose detection by researchers depends on the social context. [ABSTRACT FROM AUTHOR]

Sperm competition is a potent mechanism of postcopulatory sexual selection that has been found to shape reproductive morphologies and behaviours in promiscuous animals. Especially sperm size has been argued to evolve in response to sperm competition through its effect on sperm longevity, sperm motility, the ability to displace competing sperm, and ultimately fertilization success. Additionally, sperm size has been observed to co-evolve with female reproductive morphology. Theoretical work predicts that sperm competition may select for longer sperm but may also favour shorter sperm if sperm size trades-off with number. In this study, we studied the relationship between sperm size and postmating success in the free-living flatworm, Macrostomum lignano. Specifically, we used inbred isolines of M. lignano that varied in sperm size to investigate how sperm size translated into the ability of worms to transfer and deposit sperm in a mating partner. Our results revealed a hump-shaped relationship with individuals producing sperm of intermediate size having the highest sperm competitiveness. This finding broadens our understanding of the evolution of sperm morphology by providing empirical support for stabilizing selection on sperm size under sperm competition. Graphical Abstract [ABSTRACT FROM AUTHOR]

Male seminal fluid proteins often show signs of positive selection and divergent evolution, believed to reflect male–female coevolution. Yet, our understanding of the predicted concerted evolution of seminal fluid proteins and female reproductive proteins is limited. We sequenced, assembled, and annotated the genome of two species of seed beetles allowing a comparative analysis of four closely related species of these herbivorous insects. We compare the general pattern of evolution in genes encoding seminal fluid proteins and female reproductive proteins with those in digestive protein genes and well-conserved reference genes. We found that female reproductive proteins showed an overall ratio of nonsynonymous to synonymous substitutions (ω) similar to that of conserved genes, while seminal fluid proteins and digestive proteins exhibited higher overall ω values. Further, seminal fluid proteins and digestive proteins showed a higher proportion of sites putatively under positive selection, and explicit tests showed no difference in relaxed selection between protein types. Evolutionary rate covariation analyses showed that evolutionary rates among seminal fluid proteins were on average more closely correlated with those in female reproductive proteins than with either digestive or conserved genes. Gene expression showed the expected negative covariation with ω values, except for male-biased genes where this negative relationship was reversed. In conclusion, seminal fluid proteins showed relatively rapid evolution and signs of positive selection. In contrast, female reproductive proteins evolved at a lower rate under selective constraints, on par with genes known to be well conserved. Although our findings provide support for concerted evolution of seminal fluid proteins and female reproductive proteins, they also suggest that these two classes of proteins evolve under partly distinct selective regimes. [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]

Plutella xylostella exhibits exceptional reproduction ability, yet the genetic basis underlying the high reproductive capacity remains unknown. Here, we demonstrate that an orphan gene, lushu , which encodes a sperm protein, plays a crucial role in male reproductive success. Lushu is located on the Z chromosome and is prevalent across different P. xylostella populations worldwide. We subsequently generated lushu mutants using transgenic CRISPR/Cas9 system. Knockout of Lushu results in reduced male mating efficiency and accelerated death in adult males. Furthermore, our findings highlight that the deficiency of lushu reduced the transfer of sperms from males to females, potentially resulting in hindered sperm competition. Additionally, the knockout of Lushu results in disrupted gene expression in energy-related pathways and elevated insulin levels in adult males. Our findings reveal that male reproductive performance has evolved through the birth of a newly evolved, lineage-specific gene with enormous potentiality in fecundity success. These insights hold valuable implications for identifying the target for genetic control, particularly in relation to species-specific traits that are pivotal in determining high levels of fecundity. [ABSTRACT FROM AUTHOR]

In internal fertilisers, the precise timing of ovulation with the arrival of sperm at the site of fertilisation is essential for fertilisation success. In birds, mating is often not synchronised with ovulation, but instead females utilise specialised sperm storage tubules (SSTs) in the reproductive tract, which can ensure sperm are always available for fertilisation at the time of ovulation, whilst simultaneously providing a mechanism of post‐copulatory sexual selection. Despite the clear importance of SSTs for fertilisation success, we know little about the mechanisms involved in sperm acceptance, storage, and release. Furthermore, most research has been conducted on only a small number of species, based on which SSTs are usually assumed to look and function in the same way across all species. Here, we conduct a comparative exploration of SST morphology across 26 species of Galliformes. We show that SSTs, and the surrounding tissue, can vary significantly in morphology across species. We provide observational evidence that Galliformes exhibit at least 5 distinct categories of tubule types, including distinctive coiled and multi‐branched tubules, and describe 2 additional features of the surrounding tissue. We suggest functional explanations for variation in tubule morphology and propose next steps for future research. Our findings indicate that SSTs are likely to be far more variable than has previously been assumed, with potentially important consequences for our understanding of sperm storage in birds and post‐copulatory sexual selection in general. [ABSTRACT FROM AUTHOR]

Parallel laser photogrammetry (PLP), which consists of attaching two or three parallel laser beams at a known inter‐beam distance to a camera, can be used to collect morphological measurements of organisms noninvasively. The lasers project onto the photo being taken, and because the inter‐beam distance is known, they act as a scale for image analysis programs like ImageJ. Traditionally, this method has been used to measure larger morphological traits (e.g., limb length, crown‐rump length) to serve as proxies for overall body size, whereas applications to smaller anatomical features remain limited. To that end, we used PLP to measure the testes of 18 free‐living mantled howler monkeys (Alouatta palliata) at La Selva Biological Station, Costa Rica. We tested whether this method could reliably measure this relatively small and globular morphology, and whether it could detect differences among individuals. We tested reliability in three ways: within‐photo (coefficient of variation [CV] = 4.7%), between‐photo (CV = 5.5%), and interobserver (intraclass correlation = 0.92). We found an average volume of 36.2 cm3 and a range of 16.4–54.4 cm3, indicating variation in testes size between individuals. Furthermore, these sizes are consistent with a previous study that collected measurements by hand, suggesting that PLP is a useful method for making noninvasive measurements of testes. Research Highlights: Testes measurements are a critical data type that can elucidate key questions related to sperm competition and endocrine disruption, and deriving the measurements noninvasively is a great benefit to conservation effortsWe collected and measured photos of 18 individual adult mantled howler monkeys (Alouatta palliata) from La Selva, Costa Rica via parallel laser photogrammetryWe used three tests of repeatability to provide evidence that parallel laser photogrammetry can be used to measure the testes of a large‐bodied nonhuman primate noninvasively while being precise and accurate [ABSTRACT FROM AUTHOR]

The study investigated if gonad maturation in triploid brown trout, Salmo trutta, was entirely suppressed or only delayed, and if triploids could interbreed with diploid counterparts. Ten percent of the total number of 3‐year‐old triploid S. trutta, 15% of 4‐year‐old fish, and 17% of 5‐year‐old fish produced semen. Three and 4 years old triploid fish did not produce eggs, but 15% of the 5‐year‐old fish did so. The quantity and sperm motility of triploid semen did not differ from diploids, but the sperm concentration was significantly lower. When diploid eggs were fertilized with triploid semen (3n × 2n crosses), the percentage of eyed stage embryos, of hatched larvae, and of normal‐shaped larvae did not differ from the diploid controls. Circa 90% of 3n × 2n crosses had a ploidy level of 2.4n. In the remaining percentage of 3n × 2n crosses, the ploidy level was ≥2n and <2.4n. In sperm competition experiments where diploid eggs were fertilized with a mixture of diploid and triploid semen, 52% of the originating larvae had a ploidy level of 2n, 43% of 2.4n, and 5% of the fish were not exactly classified. From the start of feeding to an age of 248 days, the mortality rate of 3n × 2n interploid crosses and of 2n × 2n controls was similar. The growth of interploid crosses was significantly higher than that of controls. In triploid mature females, the egg mass per kilogram of body weight was significantly lower than in diploids. The mass of the non‐hardened eggs and the percentile weight increase during hardening did not differ from diploid eggs. When triploid eggs were fertilized with diploid semen (2n × 3n crosses), the development rate to normal hatched larvae was less than 10%. All originating larvae had a ploidy level of 3n. From the start of feeding to an age of 248 days, 2n × 3n crosses had a higher mortality rate (15%) than diploid controls (<5%). Growth of this type of interploid crosses was reduced in comparison to controls. Therefore, triploids introduced into natural waters for recreational fisheries or escaping from farms may interbreed with diploid counterparts. This not only alters the genotypes of local populations but also changes the ploidy levels. [ABSTRACT FROM AUTHOR]

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

Our understanding of microbial variation in male reproductive tissues is poorly understood, both regarding how it varies spatially across different tissues and its ability to affect male sperm and semen quality. To redress this gap, we explored the relationship between male sperm viability and male gut and reproductive tract microbiomes in the Pacific field cricket, Teleogryllus oceanicus. We selected cohorts of males within our populations with the highest and lowest natural sperm viability and characterized the bacterial microbiota present in the gut, testes, seminal vesicle, accessory glands and the spermatophore (ejaculate) using 16S ribosomal RNA gene metabarcoding. We identified bacterial taxa corresponding to sperm viability, highlighting for the first time an association between the host’s microbial communities and male competitive fertilization success. We also found significant spatial variation in bacterial community structure of reproductive tissue types. Our data demonstrate the importance of considering the microbial diversity of both the host gut and reproductive tract when investigating male fertility in wildlife and potentially human clinical settings.

Abstract In some squids, such as those in the family Loliginidae, upon copulation, females receive and store male-delivered sperm capsules, spermatangia, at two different body locations: the buccal membrane and the distal end of the oviduct. This insemination site dimorphism is associated with alternative reproductive strategies. However, in Loliolus sumatrensis, a species of Loliginidae, the females possess three insemination sites: buccal membrane (BM), basal left IV arm (ARM) and lateral head behind the left eye (EYE), therefore we studied such the unusual phenomena. We developed microsatellite markers and genotyped the paternity of each spermatangium on three sites. We found multiple paternity at every single site and simultaneous usage of all three sites by a few males. The seasonal dynamics of a population in the Seto Inland Sea revealed a set priority for the initial use of insemination sites as BM, followed by ARM and then EYE, whereas the maximum number of stored spermatangia was greater in EYE > ARM > BM. Female maturity status was correlated with the usage pattern of insemination sites but not with the number of stored spermatangia at any insemination site. These results suggest that a male squid inseminates at different locations according to female mating history and female maturity status.

The article is a review of a book titled "Sex in Cetaceans: Morphology, Behavior, and the Evolution of Sexual Strategies." The book consists of 24 chapters written by different authors, providing an overview of the reproductive strategies and behaviors of cetaceans. It includes new research on the reproduction of specific species of toothed and baleen whales. The chapters cover topics such as genetic tools for parentage analysis, sexual anatomy, reproductive strategies, nonconceptive sexual behavior, infanticide, and drone perspectives on mating behavior. The book also discusses the impact of human activities on cetacean reproductive health. Overall, the book is recommended for those interested in learning more about reproduction and mating systems in aquatic-living mammals. [Extracted from the article]