Understanding Of Sexual Selection Research Articles

Mating behavior of the Sydney funnel‐web spider (Atracidae: Atrax robustus) and implications for the evolution of courtship in mygalomorph spiders

AbstractSpiders have become a model group for sexual selection and mating system studies, but our understanding of courtship behavior in the group is heavily biased towards the infraorder Araneomorphae (‘modern’ spiders, such as orb weavers, jumping spiders, wolf spiders, crab spiders and many more). In the Mygalomorphae (tarantulas, trapdoor spiders, funnel‐web spiders and relatives), only a few descriptions of courtship are available and recent developments in the phylogenetics of the group offer an opportunity to remap and investigate the evolution of mating behaviors. Using 81 trials filmed in captivity, we report on the courtship behaviors of the iconic Sydney funnel‐web spider (Atracidae: Atrax robustus), which belongs to a large clade of biologically understudied mygalomorphs. Thirteen distinct behaviors are described for males, out of which at least two seem new to mygalomorphs, while four female behaviors are described. Moreover, the sequences of male behaviors are presented for when they come into contact with females inside or outside of their burrows. The mating positions of the pair, including details of how males use their legs and clasping spurs to grasp the females, are also presented. We discuss our results in a modern phylogenetic context, filling a gap in the understanding of sexual selection in the Mygalomorphae where such studies are rare and biased towards tarantulas. Finally, we attempt to consolidate descriptions of potentially homologous behaviors from several families in the group and offer insights into the evolution of cannibalism, male clasping spurs and female catalepsis (quiescence while mating).

The Unusual Value of Long-Term Studies of Individuals: The Example of the Isle of Rum Red Deer Project

Long-term studies of individuals enable incisive investigations of questions across ecology and evolution. Here, we illustrate this claim by reference to our long-term study of red deer on the Isle of Rum, Scotland. This project has established many of the characteristics of social organization, selection, and population ecology typical of large, polygynous, seasonally breeding mammals, with wider implications for our understanding of sexual selection and the evolution of sex differences, as well as for their population dynamics and population management. As molecular genetic techniques have developed, the project has pivoted to investigate evolutionary genetic questions, also breaking new ground in this field. With ongoing advances in genomics and statistical approaches and the development of increasingly sophisticated ways to assay new phenotypic traits, the questions that long-term studies such as the red deer study can answer become both broader and ever more sophisticated. They also offer powerful means of understanding the effects of ongoing climate change on wild populations.

Measuring mate preferences: Absolute and comparative evaluation of potential partners

Quantifying the direction and strength of mate preference is essential to improve our understanding of sexual selection. Experimental designs, however, often do not consider how individuals evaluate and compare the available options, which may affect the results significantly. Preferences are often assumed to be absolute, with individuals assigning a fixed, absolute value to a cue or potential partner they encounter. However, individuals may instead also compare the available options, in which case the social context plays an essential role in the preference for each potential partner. Here we investigated the importance of considering the choosers’ evaluation process in mate preference tests. Using a mate preference study on wild great tit, Parus major, heterozygosity, breast stripe size and yellowness as a case study, we tested whether individuals use absolute or comparative mate preferences. We analysed how the perceived average attractiveness and the variation in attractiveness of the group of potential mates affected the measured preference functions. We found that the average attractiveness of the stimulus groups affected the total time individuals spent visiting all stimulus birds, and that the variation in attractiveness within groups affected the measured preference slopes. This indicates that the social context will affect the measured responses to stimulus groups, and that great tits may use both absolute and comparative evaluation. Considering how a study species encounters and evaluates potential mates and how the social environment may affect preferences is essential when choosing an appropriate experimental design to obtain reliable measurements of mate preferences. We therefore strongly advise future studies to consider not only the absolute stimulus trait values, but also the context in which they are presented. The ability to quantify preferences accurately will increase our understanding of mate preferences, mate choice and ultimately sexual selection.

Bodyweight-Related Polyandry in the Tobacco Cutworm Moth Spodoptera litura (Lepidoptera: Noctuidae)

Recent studies on polyandry evolution have revolutionized our understanding of sexual selection. Therefore, study on traits in females, such as sensory perception and remating strategies, is expected to disclose a greater role of sexual selection in female evolution. Here, we tested how bodyweights of both sexes affected female and male remating behavior in Spodoptera litura (Fabricius, 1775) (Lepidoptera: Noctuidae). Results show most (74.4%; unmated virgin females may be sexually immature) females and males mated the first time in the second scotophase after eclosion. In the subsequent scotophase, 41.9% once-mated females and 94.1% once-mated males mated the second time with a novel virgin mate. Analyses indicate that female remating probability significantly increased with the increase of her own and the second male’s bodyweight but decreased with the increase of the first male’s bodyweight, while bodyweights of both sexes have no significant effect on male remating probability. Considering the nature of the low level of polyandry (two times on average) and last male precedence in S. litura, we propose that 1) females are more choosy when remating, from which females will benefit indirectly by sequential mate comparison and remate to replace sperm from the previous mates with those from higher quality mates, and 2) males will generally like to remate with any possible females, from which males will gain direct benefit by siring more offspring. The outcome of polyandry rate is likely to be the result of male investment × female choice interactions.

Sex roles and sexual selection: lessons from a dynamic model system

Our understanding of sexual selection has greatly improved during the last decades. The focus is no longer solely on males, but also on how female competition and male mate choice shape ornamentation and other sexually selected traits in females. At the same time, the focus has shifted from documenting sexual selection to exploring variation and spatiotemporal dynamics of sexual selection, and their evolutionary consequences. Here, I review insights from a model system with exceptionally dynamic sexual selection, the two-spotted goby fish Gobiusculus flavescens. The species displays a complete reversal of sex roles over a 3-month breeding season. The reversal is driven by a dramatic change in the operational sex ratio, which is heavily male-biased at the start of the season and heavily female-biased late in the season. Early in the season, breeding-ready males outnumber mature females, causing males to be highly competitive, and leading to sexual selection on males. Late in the season, mating-ready females are in excess, engage more in courtship and aggression than males, and rarely reject mating opportunities. With typically many females simultaneously courting available males late in the season, males become selective and prefer more colorful females. This variable sexual selection regime likely explains why both male and female G. flavescens have ornamental colors. The G. flavescens model system reveals that sexual behavior and sexual selection can be astonishingly dynamic in response to short-term fluctuations in mating competition. Future work should explore whether sexual selection is equally dynamic on a spatial scale, and related spatiotemporal dynamics.

Studying mate choice in the wild using 3D printed decoys and action cameras: a case of study of male choice in the northern map turtle

Mate choice experiments are essential to further our understanding of sexual selection, but can be challenging to design and conduct with most wild animals. 3D printing technology is creating opportunities to conduct mate choice experiments in the field by facilitating the production of biologically accurate decoys. We used pairs of 3D printed female decoys differing only in size to test whether free-ranging male northern map turtles, Graptemys geographica, prefer larger females. Males interacted and attempted to mate significantly more with the larger decoys. By selecting larger females, males should increase their fitness because of the correlation between female size and hatchling size. Our experiment demonstrated that 3D printing technology can be a valuable tool to study animal behaviour in the field.

Macroecology of Sexual Selection: A Predictive Conceptual Framework for Large-Scale Variation in Reproductive Traits.

Abiotic factors exert direct and indirect influences on behavioral, morphological, and life-history traits. Because some of these traits are related to reproduction, there is a causal link between climatic conditions and the expression of reproductive traits. This link allows us to generate predictions on how reproductive traits vary in large geographic scales. Here we formalize this macroecological framework, present some general predictions, and explore empirical examples using harvestmen as study organisms. Our results show that the length of breeding season in harvestmen is primarily influenced by the number of warm months and that precipitation plays a secondary role in modulating the period devoted to reproduction. Moreover, we show that the probability of resource defense polygyny increases with longer breeding seasons and that the presence of this type of mating system positively affects the magnitude of sexual dimorphism in harvestmen. Finally, the presence of postovipositional parental care is also influenced by the length of breeding season but not by actual evapotranspiration, which is our proxy for the intensity of biotic interactions. We argue that the macroecological framework proposed here may be a fruitful field of investigation, with important implications for our understanding of sexual selection and the evolution of reproductive traits in both animals and plants.

配偶选择中“听众效应”及鸣唱对雌性灰文鸟行为的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 配偶选择中“听众效应”及鸣唱对雌性灰文鸟行为的影响 DOI: 10.5846/stxb201501290238 作者: 作者单位: 辽宁大学生命科学院,辽宁大学生命科学院,辽宁大学生命科学院,辽宁大学生命科学院,辽宁大学生命科学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31100271） Effects of “audience effects” and song on female Padda oryzivora mate choice behavior Author: Affiliation: Department of Life Sciences, Liaoning University,,,,Department of Life Sciences, Liaoning University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:配偶选择是性选择研究核心问题之一。雌性通过选择高质量的雄性配偶获得直接利益，如资源、营养和保护等，也可以通过获得高质量雄性提高后代的适合度。配偶选择研究对于研究性选择机制和进化均具有重要意义。目前，对配偶选择的研究主要集中在影响配偶选择的因素及雌性"听众效应"中雄性-雄性竞争方面。鸣唱对配偶选择的影响和雄性"听众效应"中雌性-雌性竞争的研究对于探索鸟类配偶选择中信号交流、调整的方式及选择策略均具有重要意义。以灰文鸟为对象，研究了雄性鸣唱对雌性配偶选择的影响及雄性"听众效应"对雌性灰文鸟同性竞争行为的影响进行了探讨。实验一利用双向选择装置，以配偶鸣唱（求偶鸣唱或非求偶鸣唱）和非配偶鸣唱（求偶鸣唱或非求偶鸣唱）对雌鸟进行刺激，观察雌鸟对两端鸣唱的偏爱状况。实验二主要观察雌鸟之间在无听众、听众为熟悉的雄性和听众为配偶条件下的竞争行为。结果表明，雌性灰文鸟大多偏爱配偶鸣唱，相对于配偶的非求偶鸣唱更偏爱非配偶的求偶鸣唱。求偶鸣唱比非求偶鸣唱更具有吸引力，求偶鸣唱更能刺激雌性灰文鸟配偶选择的积极性，这种积极要付出更多的时间和资源，但雌鸟可以通过选择更高质量的雄性配偶获益。在配偶雄性作为听众条件下雌鸟攻击行为最高，显著高于熟悉雄性为听众的条件下，并且两者都显著高于无听众条件下雌鸟的攻击行为。雌性灰文鸟会基于不同"听众"而对雌-雌竞争行为做出适当调整。上述研究结果对于深入理解鸟类的性选择行为机制具有重要帮助作用。 Abstract:Mate choice is one of the most important aspects of sexual selection, and uncovering the mechanisms behind mate choice is a central issue in sexual selection studies. Females choose high-quality males as mates to obtain direct benefits such as resources, nutrition, and protection, and in doing so they acquire indirect genetic benefits for future generations. Further studies of female mate choice would improve our understanding of sexual selection and evolutionary processes. Song is one of the most important secondary sexual characteristics in birds and can reflect male territory quality and genetic and physiological status. Females can extract information about male quality by assessing their songs, and more complex songs are preferred over simple ones. Birds inhabit a communication network in which individuals can assess the quality of potential mates by visual and auditory observation of their interactions. In addition, individuals being observed may adjust their signaling behavior. Audience effects are defined as changes in signaling behavior of an individual engaged in an interaction due to the presence of an audience consisting of a conspecific witnessing the interaction. To date, studies of sexual selection have mainly focused on the driving factors of mate choice and on female audience effects on female-female competition. In contrast, there is limited knowledge about the effects of bird song on mate choice and about male audience effects on female-female competition. Here, we investigated the effects of male song on female mate choice and the male audience effect on female-female competition in Padda oryzivora. In the first part of the study, we used a two-way choice device and stimulated the female by courtship or other songs of a spouse and other males, and we observed female song preference. In the second part of the study, females were observed under three conditions: (a) in the absence of an audience, (b) in the presence of a familiar male, and (c) in the presence of a mate. Our results showed that female P. oryzivora preferred the spouse's song and preferred courtship songs of other males to the non-courtship song of their mates. The courtship song was more attractive than other songs, and its effects were much stronger in stimulating positive female mate choice. The courtship chirp caused a positive response in the female. Females expended more time and resources, but also benefited more, by selecting higher-quality mates. Female P. oryzivora were more aggressive in the presence than in the absence of a male and were more aggressive in the presence of the mate than in the presence of a familiar male. Females appropriately adjust female-female competition behavior when under the male audience effect; whether this is a result of males choosing mates by observing this competition remains to be examined, as does female-female competition in the wild. These results improve our understanding of the underlying mechanism of mate choice behavior in birds. 参考文献 相似文献 引证文献

Stepping off the pasture: evidence of widespread alternative male mating tactics in the yellow dung fly

Geoff Parker’s investigations of the yellow dung fly mating system revitalized interest in sexual selection theory, sparked development of sperm competition and sexual conflict theories, and stimulated use of this species as an important model system. Numerous studies across widespread populations have demonstrated large-male advantages in competition contests occurring on dung in cow pastures; however, recent work suggests that smaller males adopt an alternative mating tactic by avoiding dung and instead copulating with females at foraging sites. Though this finding has the potential to expand our understanding of sexual selection in yellow dung flies, such behavior has to date been documented at only one field site, raising the possibility that this phenomenon is highly localized. Here, we report the expression of size-dependent alternative mating tactics across three discrete populations. These findings provide a cautionary tale for researchers limiting their attention to aggregation sites where study organisms are most conveniently encountered.

Female discrimination thresholds frequently exceed local male display variation: implications for mate choice dynamics and sexual selection.

Among the factors that can influence female mate choice decisions is the degree to which females differentiate among similar displays: as differences decrease, females are expected to eventually stop discriminating. This discrimination threshold, in conjunction with the magnitude of male trait variation females regularly encounter while making mate choice decisions, may have important consequences for sexual selection. If local display variation is above the discrimination threshold, female preferences should translate into higher mating success for the more attractive male. But if display variation is frequently below the threshold, the resulting increased pattern of random mating may obscure the existence of female mate choice. I investigated the interplay between female discrimination and male display variation in green treefrogs (Hyla cinerea) and found that call trait differences between nearest neighbour males were frequently smaller than what females are expected to discriminate. This finding has two important consequences for our understanding of sexual selection in the wild: first, low display variation should weaken the strength of selection on male display traits, but the direction of selection should mirror the one predicted from females choice trials. Second, caution is needed when interpreting data on realized mating success in the wild: a pattern of random mating with respect to male display traits does not always mean that female preferences are weak or that conditions are too challenging for females to express their preferences. Rather, insufficient display variation can generate the same pattern.

Effects of Age and Experience on Male Mate Choosiness

AbstractMate choosiness by males has been documented in many taxa but we still do not know how it varies with age even though such variation can be important for our understanding of sexual selection on females. Theory provides conflicting predictions: young males, who are less attractive to females than older males, may be less choosy, or older males, who face fewer expected future mating opportunities, may be less choosy. In our experiments with fruit flies (Drosophila melanogaster), young (1‐d‐old) males spent relatively less time courting recently mated females than did mature (4‐d‐old) males. Overall, there was a gradual decline in male mate choosiness from age 1–7 d. As male age was correlated with the duration of deprivation from females, we tested for the effect of deprivation and found that same‐age males previously exposed to females were choosier than female‐deprived males. We also assessed key male parameters that could affect choosiness and found that, compared to mature males, young males were less attractive to females, less competitive in intramale interactions and less fertile. Although the lesser attractiveness and competitiveness should select for lesser mate choosiness in young males, their limited fertility and more expected future mating opportunities seem to override the other factors and lead to high mate choosiness in young males. Overall, our data indicate that young males just after reaching sexual maturity are choosy and that subsequent exposure to females can maintain high levels of male mate choosiness with age. Hence, males can contribute much more to sexual selection than previously appreciated.

Individual and environmental determinants of reproductive success in male tree swallow (Tachycineta bicolor)

Evaluating the contribution of individual and environmental determinants of reproductive success is essential to improve our understanding of sexual selection. In socially monogamous bird species with high rates of extrapair paternity, traits or environmental contexts affecting the number of within-pair young (WPY) produced by males can differ from those affecting the number of extrapair young fathered (EPY). Here, we use a 4-year dataset collected in contrasted environments to assess the factors affecting male reproductive success in tree swallows (Tachycineta bicolor), a species showing high levels of extrapair paternity. Our analyses revealed that the number of WPY was higher under better environmental conditions, while the number of EPY was mainly related to male characteristics. Males nesting in more intensive agricultural areas had fewer WPY produced and a lower reproductive success. Also, males breeding earlier in the season had more WPY. The presence of parasites reduced males’ reproductive success, mainly by reducing the number of EPY. The influence of male phenotype varied according to population density: Tarsus length variation had a greater effect on reproductive success at low population density than at high density, while wing length was also positively related to the number of EPY, more so at high than at low density. Altogether, our results suggest a complex interplay between individual and environmental determinants of reproductive success and imply that sexual selection dynamics varies depending on environmental contexts.

Hemiclonal analysis of interacting phenotypes in male and female Drosophila melanogaster.

BackgroundIdentifying the sources of variation in mating interactions between males and females is important because this variation influences the strength and/or the direction of sexual selection that populations experience. While the origins and effects of variation in male attractiveness and ornamentation have received much scrutiny, the causes and consequences of intraspecific variation in females have been relatively overlooked. We used cytogenetic cloning techniques developed for Drosophila melanogaster to create “hemiclonal” males and females with whom we directly observed sexual interaction between individuals of different known genetic backgrounds and measured subsequent reproductive outcomes. Using this approach, we were able to quantify the genetic contribution of each mate to the observed phenotypic variation in biologically important traits including mating speed, copulation duration, and subsequent offspring production, as well as measure the magnitude and direction of intersexual genetic correlation between female choosiness and male attractiveness.ResultsWe found significant additive genetic variation contributing to mating speed that can be attributed to male genetic identity, female genetic identity, but not their interaction. Furthermore we found that phenotypic variation in copulation duration had a significant male-associated genetic component. Female genetic identity and the interaction between male and female genetic identity accounted for a substantial amount of the observed phenotypic variation in egg size. Although previous research predicts a trade-off between egg size and fecundity, this was not evident in our results. We found a strong negative genetic correlation between female choosiness and male attractiveness, a result that suggests a potentially important role for sexually antagonistic alleles in sexual selection processes in our population.ConclusionThese results further our understanding of sexual selection because they identify that genetic identity plays a significant role in phenotypic variation in female behaviour and fecundity. This variation may be potentially due to ongoing sexual conflict found between the sexes for interacting phenotypes. Our unexpected observation of a negative correlation between female choosiness and male attractiveness highlights the need for more explicit theoretical models of genetic covariance to investigate the coevolution of female choosiness and male attractiveness.

What does carotenoid-dependent coloration tell? Plasma carotenoid level signals immunocompetence and oxidative stress state in birds-A meta-analysis.

Mechanisms maintaining honesty of sexual signals are far from resolved, limiting our understanding of sexual selection and potential important parts of physiology. Carotenoid pigmented visual signals are among the most extensively studied sexual displays, but evidence regarding hypotheses on how carotenoids ensure signal honesty is mixed. Using a phylogenetically controlled meta-analysis of 357 effect sizes across 88 different species of birds, we tested two prominent hypotheses in the field: that carotenoid-dependent coloration signals i) immunocompetence and/or ii) oxidative stress state. Separate meta-analyses were performed for the relationships of trait coloration and circulating carotenoid level with different measures of immunocompetence and oxidative stress state. For immunocompetence we find that carotenoid levels (r = 0.20) and trait color intensity (r = 0.17) are significantly positively related to PHA response. Additionally we find that carotenoids are significantly positively related to antioxidant capacity (r = 0.10), but not significantly related to oxidative damage (r = −0.02). Thus our analyses provide support for both hypotheses, in that at least for some aspects of immunity and oxidative stress state the predicted correlations were found. Furthermore, we tested for differences in effect size between experimental and observational studies; a larger effect in observational studies would indicate that co-variation might not be causal. However, we detected no significant difference, suggesting that the relationships we found are causal. The overall effect sizes we report are modest and we discuss potential factors contributing to this, including differences between species. We suggest complementary mechanisms maintaining honesty rather than the involvement of carotenoids in immune function and oxidative stress and suggest experiments on how to test these.

Does Animal Behavior Underlie Covariation Between Hosts’ Exposure to Infectious Agents and Susceptibility to Infection? Implications for Disease Dynamics

Animal behavior is unique in influencing both components of the process of transmission of disease: exposure to infectious agents, and susceptibility to infection once exposed. To date, the influence of behavior on exposure versus susceptibility has largely been considered separately. Here, we ask whether these two key mechanisms act in concert in natural populations, whereby individuals who are most exposed to infectious agents or have the most contact with conspecifics are also the most susceptible or infectious. We propose three mechanisms that can generate covariation between these two key elements of the transmission of disease within and among hosts, and we provide empirical examples of each. We then use a mathematical model to examine the effect of this covariation on the dynamics of disease at the population level. First, we show that the empirical mechanisms generating covariation between behavioral and physiological components of disease transmission are widespread and include endocrine mediators of behavior, mate choice, group size, sickness behaviors, and behavioral avoidance of infectious conspecifics. The diversity of these empirical mechanisms underscores the potential importance and breadth of covariation in the disease process. Second, we show mathematically that the variability in hosts' exposure to infectious agents and susceptibility or infectiousness, and how tightly they are coupled, strongly influences the ability of a disease to invade a host population. Overall, we propose that covariation between behavioral and physiological components of transmission is likely widespread in natural populations, and can have important consequences for the dynamics of disease at the population level as well as for our understanding of sexual selection, social behavior, and animal communication.

Mate choice for cognitive traits: a review of the evidence in nonhuman vertebrates

To what extent do individuals assess the cognitive abilities of the opposite sex when choosing a mate? With the exception of song learning in birds, the hypothesis that cognitive traits are under sexual selection has received attention only recently. Here, we evaluate the evidence for this hypothesis in nonhuman vertebrates. We first briefly review the literature on brain development, which shows that cognition may be a sensitive indicator of early developmental conditions. We then consider the empirical evidence that females choose mates with better cognitive skills, which may be reflected in males' courtship displays, foraging performance, courtship feeding, or diet-dependent morphological traits. There is very little research that assesses whether females discriminate between males through direct observation of cognitively demanding behavior. Instead, several studies support female choice on the basis of morphological traits correlated with cognitive abilities. We conclude by highlighting key questions for future research: 1) To what extent do cognitive skills determine foraging success, courtship feeding, and the expression of diet-dependent morphological traits? 2) Do behavioral courtship displays depend on motor development and physiological maturation or learning through practice and experience? 3) How do cognitive abilities affect survival and mating success? Studies on a range of vertebrate taxa, with their diverse mating systems and cognitive ecologies, offer great potential to tackle these questions and deepen our understanding of sexual selection on cognition. Copyright 2011, Oxford University Press.

The Genetic Basis of Sexually Selected Variation

Sexually selected traits contribute greatly to phenotypic diversity, yet we have historically understood little about their genetic basis and how that basis may affect their evolution. Recent work in developmental and quantitative genetics has provided both mechanistic and statistical descriptions of genotype-phenotype maps for sexually selected traits. These studies expose generally complex genetic architectures; genotype-phenotype maps are polygenic with allelic effects that are pleiotropic and highly context-dependent. At the same time, developments in quantitative genetics have provided new insights into the microevolutionary potential of standing variation and indicate genetic constraints on the contemporary evolution of male sexually selected characters, mate preferences, and also male mating success itself. Understanding the extent to which these constraints are a function of genetic architecture will require a tighter integration of developmental, molecular, and quantitative genetic approaches in a variety of model systems. Emerging genomic technologies offer an unprecedented opportunity to deepen our understanding of sexual selection as an evolutionary process.

Bateman Gradients in Hermaphrodites: An Extended Approach to Quantify Sexual Selection

Sexual selection is often quantified using Bateman gradients, which represent sex-specific regression slopes of reproductive success on mating success and thus describe the expected fitness returns from mating more often. Although the analytical framework for Bateman gradients aimed at covering all sexual systems, empirical studies are biased toward separate-sex organisms, probably because important characteristics of other systems remain incompletely treated. Our synthesis complements the existing Bateman gradient approach with three essential reproductive features of simultaneous hermaphrodites. First, mating in one sex may affect fitness via the opposite sex, for example, through energetic trade-offs. We integrate cross-sex selection effects and show how they help characterizing sexually mutualistic versus antagonistic selection. Second, male and female mating successes may be correlated, complicating the interpretation of Bateman gradients. We show how to quantify the impact of this correlation on sexual selection and propose a principal component analysis on male and female mating success to facilitate interpretation. Third, self-fertilization is accounted for by adding selfed progeny as a separate category of reproductive success to analyses of Bateman gradients. Finally, using a worked example from the snail Biomphalaria glabrata, we illustrate how the extended analytical framework can enhance our understanding of sexual selection in hermaphroditic animals and plants.

Low level of extrapair parentage in wild zebra finches

The captive zebra finch, Taeniopygia guttata, has become one of the key vertebrate model systems for studying a range of behavioural, physiological and neurological phenomena. In particular, this species has played a key role in developing our understanding of sexual selection and sperm competition. In contrast with the large number of studies using domesticated zebra finches, relatively few studies have focused on free-living populations of wild zebra finches. Investigating the incidence of extrapair paternity in zebra finches in the Australian desert, we found a very low level; 1.7% of 316 offspring from four of 80 broods fathered outside the pair bond. These numbers contrast with the high levels of extrapair paternity observed in domesticated aviary populations, and suggest a low level of sperm competition and sexual selection in natural populations. Our finding of such a low rate of extrapair paternity in the wild zebra finch suggests that it is one of the most genetically monogamous of all passerine species and that has important implications for future studies of this model organism in studies of sexual selection and reproductive biology. In addition, we found that 5.4% of 316 offspring were not related to either putative parent and hatched from eggs that had been dumped by intraspecific brood parasites.

PURGING THE GENOME WITH SEXUAL SELECTION: REDUCING MUTATION LOAD THROUGH SELECTION ON MALES

Healthy males are likely to have higher mating success than unhealthy males because of differential expression of condition-dependent traits such as mate searching intensity, fighting ability, display vigor, and some types of exaggerated morphological characters. We therefore expect that most new mutations that are deleterious for overall fitness may also be deleterious for male mating success. From this perspective, sexual selection is not limited to influencing those genes directly involved in exaggerated morphological traits but rather affects most, if not all, genes in the genome. If true, sexual selection can be an important force acting to reduce the frequency of deleterious mutations and, as a result, mutation load. We review the literature and find various forms of indirect evidence that sexual selection helps to eliminate deleterious mutations. However, direct evidence is scant, and there are almost no data available to address a key issue: is selection in males stronger than selection in females? In addition, the total effect of sexual selection on mutation load is complicated by possible increases in mutation rate that may be attributable to sexual selection. Finally, sexual selection affects population fitness not only through mutation load but also through sexual conflict, making it difficult to empirically measure how sexual selection affects load. Several lines of enquiry are suggested to better fill large gaps in our understanding of sexual selection and its effect on genetic load.