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In general, males mate with multiple females to increase individual reproductive success. Whether or not, and under what circumstances, females benefit from multiple mating has been less clear. Our review of 154 studies covering 184 populations of amphibians and reptiles showed that polyandry was widespread and variable among and within taxonomic groups. We investigated whether amphibian and reptile females had greater reproductive output as the number of sires for offspring increased. Meta-analysis revealed significant heterogeneity in the dataset of all taxa. Expected heterozygosity was a significant moderator (covariate) of positive relationships between female reproductive output and the number of sires, but a sensitivity test showed the result was tenuous. Significant heterogeneity remained despite controlling for expected heterozygosity and other variables but was resolved for most taxonomic groups with subgroup meta-analyses. Subgroup meta-analyses showed that only female salamanders (Caudata) had significantly greater reproductive output with an increased number of sires. For many species of Caudata, males cannot coerce females into accepting spermatophores. We therefore suggest that if females control the number of matings, they can use polyandry to increase their fitness. Caudata offers ideal models with which to test this hypothesis and to explore factors enabling and maintaining the evolution of female choice. Outstanding problems may be addressed by expanding taxonomic coverage and data collection and improving data reporting. Significance StatementMany factors and combinations of factors drive polyandry. Whether or not females benefit from mating with more than one male remains equivocal. Focusing on amphibians and reptiles, our analyses demonstrate that female salamanders produced more offspring when mated with multiple males, whereas this was not the case for reptiles. Unlike many other species in our dataset, the polyandrous female salamanders fully control sperm intake and have chosen to mate multiple times. We further highlight problems and key directions for future research in the field.

Urbanization is a human‐induced process of rapid habitat change that can affect the reproductive success of animals. The occurrence of extra‐pair paternity (EPP) may be sensitive to changes in urban ecological conditions. In this study, the Chinese blackbird Turdus mandarinus, a common breeding bird in southern Chinese cities, was selected as the focus species to explore the EPP patterns of monogamous birds in developing cities and the relationship between pairs. Over four breeding seasons, 316 Chinese blackbird nestlings and 20 adults in both urban and rural areas were monitored and genotyped for 11 microsatellite loci to determine progeny affinity. We confirmed that both the brood size and hatching rate of EPP nests were significantly larger than those of within‐pair paternity (WPP) nests. The body mass, beak length, head length, and body length of 12‐day age extra‐pair offspring (EPO) were significantly greater than those of within‐pair offspring (WPO), suggesting important benefits of EPP. However, in accordance with the analyses of nest ecological variables, we concluded that EPP occurs most often in areas with low urbanization levels, indicating some constraints for this reproductive strategy in cities. Our findings provide new insights about how this growing human‐induced landscape change affects mating behaviour in birds, an important aspect in avian ecology and evolution.

Abstract Group-living species are often organized into social dominance hierarchies, where high-ranking individuals have priority of access to resources, including estrous females. Traits associated with male dominance status should thus be correlated with reproductive success, but, with the exception of research on some primates, studies with both behavioral data to determine dominance hierarchies and a pedigree to identify male siring success are rare. For a wild population of sexually dimorphic eastern grey kangaroos Macropus giganteus, we characterized the social hierarchy over 6 non-consecutive years to investigate the relationship between male dominance and yearly reproductive success. Dominance hierarchies were steep, linear, and stable over time. Asymmetries in body mass and size between contestants were strong predictors of contest outcomes, and these morphological traits were positively correlated with dominance status. Males did not spatially avoid each other but tended to fight with individuals of similar size, suggesting that when asymmetries were large, contests were unlikely. Dominance status was under strong sexual selection, despite moderate monopolization of paternities by highly dominant males. Overall, these results suggest that body size and weapons are important determinants of dominance status and male reproductive success but that other traits play a considerable role. A clear-cut dominance hierarchy and strong selection on dominance status do not necessarily lead to monopolization of reproduction by the most dominant males in this strongly sexually dimorphic species.Significance statementIt is generally assumed that high social rank in males is a very strong determinant of access to mates in polygamous species. Like other sexually dimorphic species, male kangaroos are thought to establish dominance hierarchies based on size. A few high-ranking males are then believed to monopolize matings. Our study confirms a strong correlation between body size and dominance status, and that males mostly engage in contests with males of similar size. However, we also found weak monopolization of reproduction, despite strong, positive sexual selection on dominance status. This result suggests that strong selection for high rank does not imply that subordinate males cannot sire offspring. A few highly dominant males had high reproductive success but did not monopolize matings.

Abstract In traditional definitions of endurance rivalry, individuals compete to remain reproductively active longer than their rivals, but these time periods are typically brief, such as a single breeding season. Here, we explored endurance rivalry among adult males in a long-lived species that breeds year-round, the spotted hyena (Crocuta crocuta). We found that most dispersing males navigated the adaptive challenges of remaining in their new clans (“enduring”) for over 2 years before siring their first cub. Additionally, sires remained in their new clans at least 4 years, whereas males that never sired any cubs typically disappeared by their fourth year of tenure. This suggests that males might incorporate their initial reproductive success in the clan into their decisions regarding whether to “endure” by remaining in the current clan or to disperse again to another clan. Finally, we used Bayesian mixed modeling to explore variation in annual male reproductive success, which we found to have a positive linear relationship with tenure and a quadratic relationship with age. A male’s rate of social associations with adult females, but not aggressive interactions with those females, was predictive of his annual reproductive success. We also found substantial individual variation in annual reproductive success across males. Our results support the notion that male spotted hyenas compete via an extended endurance rivalry; tenure unequivocally improves male reproductive success, but advanced age does not, and questions remain regarding other traits that might be salient to the rivalry or to female mate choice in this species.Significance statementSome animals compete indirectly for mates by trying to outlast their competitors during a finite breeding season; individuals that can endure the longest in this “marathon” reap the reproductive rewards. Male spotted hyenas face a different challenge because females breed year-round, so the competition to remain viable as mates is seemingly endless. Here, we show that male spotted hyenas seem to make decisions about whether to stay in a clan based on their initial reproductive success in that clan. For males with early success, the longer they stay and the more time they spend with females, the more cubs they sire each year. Our findings suggest that male spotted hyenas compete for mating opportunities via an “ultramarathon” in which they must remain in a single social group at the bottom of the hierarchy for many years to demonstrate to females their ability to endure.

Measuring individual reproductive success in the wild is often achieved by counting the number of descendants produced by individuals. In seeking to understand how reproductive success can inform us about natural selection, however, we are faced with a conundrum. In terms of timing, what is the most relevant measure for examining selection? We might count the number of offspring born, surviving to the termination of parental care, surviving to adulthood, or only those surviving to themselves reproduce. Clearly, only the latter are passing on genes and traits to future generations, but this estimate may not always be available. So, are different estimates of fitness consistent? Do they provide us with similar inferences of selection on phenotypic traits? We examined these questions on a 29-year long-term study of individually monitored male and female Columbian ground squirrels (Urocitellus columbianus). We used the long-term data to calculate male and female fitness based on an annual measure of adult survival and the yearly production of offspring counted at the stages of birth, weaning, and yearling age. We then decomposed fitness into its constitutive elements including (1) adult survival to the next spring, and (2) the yearly production of offspring counted at the stages previously mentioned. We then compared fitness metrics to evaluate if they provided similar or contrasting information in the wild. Next, we used those fitness metrics to test for selection on the date of emergence from annual hibernation, a phenotypic trait previously shown to be highly variable, heritable, and associated with reproduction. Finally, we partitioned selection on emergence date into additive episodes of selection by looking at how selection changed from reproduction measured at birth, weaning, and when offspring reached yearling age. Overall, fitness metrics were well correlated, but correlations weakened the further offspring were counted from birth. We generally found directional selection for earlier emergence dates both in males and females. The strength of selection depended on which fitness metric was used. Most of the selection gradient on emergence date was explained by offspring born, and the selection differential was stronger in males than females. We evaluate how the choice of fitness metrics in life-history studies may nuance our inferences about natural selection.Significance statementThis study explores how our inferences about natural selection acting on organismal traits vary depending on our choice of fitness metrics. Focusing on the timing of emergence from hibernation in Columbian ground squirrels, we show that directional selection for earlier emergence dates occurs, but the strength of selection depends on whether fitness is evaluated from offspring counted at birth, at weaning, or later in life. These results show that the choice of timing for fitness measurements may nuance inferences about natural selection in life-history studies.

Abstract Owing to sex-specific reproductive strategies, the mean and variance in annual offspring production may differ between the sexes. In addition, there may be sex-specific changes in reproductive performance with age (e.g. senescence). We used 20 and 50 years of longitudinal data on male and female yellow-bellied marmots, respectively, to investigate sex-specific age effects and genetic variance in annual reproductive success. In both sexes, annual offspring production increased linearly with age until a peak was reached at 7 years. This was followed by a decline in annual offspring production in both sexes, indicative of reproductive senescence. However, the initial increase and the subsequent decline (senescence) in reproductive success were both faster in males compared to females. Genetic variance in annual offspring production was higher in males than in females, but heritability was low for both sexes. Additionally, we found no cross-sex genetic correlation in the number of offspring produced, possibly reflecting sex-specific selection related to the inter-sexual differences in reproductive strategies. There was an effect of year on annual offspring production in both sexes, with a high yearly correlation between the sexes emphasizing the importance of environmental variation in determining fitness. Overall, these results demonstrate the impact of sex-specific reproductive strategies on annual offspring production and suggest that male and female marmots may be evolving to separate phenotypic optima. This study further demonstrates the value and limitations of long-term studies investigating sex-based patterns of ageing in the wild.SignificanceThis study on yellow-bellied marmots demonstrates the key constraints surrounding the research of age-related changes in reproduction in wild populations, which is especially challenging in males. Among these challenges are high immigration rates which prevent the estimation of exact age and maternal identity. Genetic analysis—the only reliable way to estimate paternity—has only been a recent development, limiting the number of father-son relationships available for analysis. The dataset used in this study is long term (20 years of data on males and 50 on females), partially overcoming these obstacles. Results show that reproductive success declines with age in both sexes, with a faster rate of decline in males compared to females, and is influenced by the environment. Genetically, male and female reproductive success is not correlated, revealing that both sexes may be following separate evolutionary trajectories.

Plant-animal interactions are pivotal for ecosystem functioning, and usually form complex networks involving multiple species of mutualists as well as antagonists. The costs and benefits of these interactions show a strong context-dependency directly related to individual variation in partner identity and differential strength. Yet understanding the context-dependency and functional consequences of mutualistic and antagonistic interactions on individuals remains a lasting challenge. We use a network approach to characterize the individual, plant-based pollination interaction networks of the Canarian Isoplexis canariensis (Plantaginaceae) with a mixed assemblage of vertebrate mutualists (birds and lizards) and invertebrate antagonists (florivores, nectar larcenists, and predispersal seed predators). We identify and quantify interaction typologies based on the sign (mutualistic vs. antagonistic) and strength (weak vs. strong) of animal-mediated pollination and test the relationship with individual female reproductive success (FRS). In addition, we document pollinator movement patterns among individual plants to infer events of pollen transfer/receipt that define the plant mating networks and test the relationship with FRS. We identify six interaction typologies along a mutualism-antagonism gradient, with two typologies being over-represented involving both mutualists and antagonists and influencing FRS. Plants showing strong mutualistic interactions, but also (weak or strong) interactions with antagonists are relatively better connected in the mating network (i.e., with higher potential to transfer or receive pollen). Thus, mixed flower visitor assemblages with mutualists and antagonists give plants increased their importance in the mating networks, promote outcrossing and increasing both female and male fitness. Our approach helps characterize plant-animal interaction typologies, the context-specificity of diversified mutualisms, and a better forecasting of their functional consequences.

Although males often disperse to increase their immediate access to mates, it is unclear whether they also consider potential future reproductive opportunities. We investigated whether immediate or delayed reproductive opportunities predicted dispersal decisions and reproductive success of subordinate immigrant male white-faced capuchins in the Sector Santa Rosa, the Área de Conservación Guanacaste, Costa Rica. We collected genetic, behavioral, and demographic data from four social groups across 20 years. We genotyped individuals at up to 20 short tandem repeat loci to determine paternity. Having previously sired offspring in a group did not predict the subordinate immigrant male’s likelihood of staying or dispersing. Instead, a male was more likely to remain in the group if he was younger and likely to benefit from queuing for future reproductive opportunities. Subordinate immigrant males were more likely to sire offspring if they resided with a long-term alpha male and his mature daughters, who avoid inbreeding. Reproductive output was similar among three categories of males: those that became alpha immediately after immigration, those that became alpha after queuing, and subordinate males that resided with a long-term alpha male and his mature daughters. These three categories of males had higher reproductive success than subordinates who did not reside with mature daughters of the alpha male. Waiting for reproductive opportunities can lead to high reproductive success and could be important in maintaining tolerant or cooperative male-male relationships in species with high reproductive skew, long alpha male tenures, and intense between-group mating competition requiring cooperative male group defense.Significance statementWe used 20 years of data from white-faced capuchins to assess whether male dispersal decisions were predicted by actual reproduction, perceived reproductive opportunities, or future reproductive opportunities and whether male reproduction was predicted by demographic factors and the male’s social position. Immigrant subordinate males were less likely to disperse from the group if they were younger and likely to benefit from queuing for future reproductive opportunities. Subordinate males residing in groups with a long-term alpha male and his mature daughters produced a similar number of offspring as did alpha males. Queuing for reproductive opportunities may maintain cooperative male-male relationships in populations with high reproductive skew and long alpha male tenures. Because these patterns only become apparent over time, our study highlights the importance of taking longitudinal paternity patterns into account to understand the evolution of dispersal and cooperation in long-lived species.

The spatial distribution of relatives has profound effects on kin interactions, inbreeding, and inclusive fitness. Yet, in the marine environment, the processes that generate patterns of kin structure remain understudied because larval dispersal on ocean currents was historically assumed to disrupt kin associations. Recent genetic evidence of co-occurring siblings challenges this assumption and raises the intriguing question of how siblings are found together after a (potentially) disruptive larval phase. Here, we develop individual-based models to explore how stochastic processes operating at the individual level affect expected kinship at equilibrium. Specifically, we predict how limited dispersal, sibling cohesion, and variability in reproductive success differentially affect patterns of kin structure. All three mechanisms increase mean kinship within populations, but their spatial effects are markedly different. We find that (1) when dispersal is limited, kinship declines monotonically as a function of the distance between individuals; (2) when siblings disperse cohesively, kinship increases within a site relative to between sites; and (3) when reproductive success varies, kinship increases equally at all distances. The differential effects of these processes therefore only become apparent when individuals are sampled at multiple spatial scales. Notably, our models suggest that aggregative larval behaviors, such as sibling cohesion, are not necessary to explain documented levels of relatedness within marine populations. Together, these findings establish a theoretical framework for disentangling the drivers of marine kin structure.

1. Patterns of male reproductive allocation provide insight into life-history characteristics. The trade-offs associated with resource and female group defence are well-defined. However, less is understood about trade-offs in species that practise scramble-competition polygyny, where successful strategies may favour competitive mate-searching rather than contest competition and fighting. 2. White-tailed deer (Odocoileus virginianus) practise scramble-competition polygyny where solitary males search for and assess receptivity of females scattered across the landscape. Physically mature males are expected to do most of the breeding because of the high energetic costs of reproduction and high social status. However, young males may collectively sire one-third of offspring. To gain a better understanding of trade-offs associated with scramble-competition polygyny, we quantified metrics associated with reproductive effort and success. 3. We quantified changes in body mass of harvested males, energetic costs of locomotion based on movements of GPS radiocollared males and timing of reproduction via temporal genetic parentage assignments. 4. Young males (1.5 and 2.5 years old) sired offspring, but their mating success was mainly limited to peak rut, when most females were in oestrus. Furthermore, multiple paternity was common, indicating opportunistic reproduction. Reproductive effort, indexed by body mass loss, was highest in prime-age males (5.5-6.5 years old). Surprisingly, young and postprime males also exhibited significant body mass loss, indicative of investment in reproductive effort. Movement rates increased twofold to fourfold during rut as a function of mate search activities, but cost of locomotion would cause only about one-third of observed body mass loss. Because males are capital breeders, we infer most of body mass loss is due to reduced foraging. 5. In scramble-competition polygyny, the repeated location of potential mates and assessment of their oestrous status appear to be important constituents of male mating strategies. Therefore, mating success may be influenced by time management and spatial memory, and not based solely on social dominance. Thus, reproductive effort should be greater for individuals capable of reducing time foraging. For those that cannot, opportunistic mating opportunities may arise when operative adult sex ratios are low. Our analyses reveal valuable insight into the trade-offs associated with scramble-competition polygyny.