What is behind the variation in mate quality dependent sex ratio adjustment? – A meta‐analysis

Theory predicts that parents adjust the sex ratio of their brood to the sexually selected traits of their mate because the reproductive success of sons may be more dependent on inherited paternal attractiveness than that of daughters. Empirical studies vary in terms of whether they support the theory, and this variation has often been regarded as evidence against sex ratio adjustment or has been ascribed to methodological differences. Applying phylogenetic meta‐analyses, we aimed to find biological explanations for the variation observed in songbirds. In particular, we tested the role extra‐pair paternity, because infidelity occurs in the majority of these species and may reduce the adaptive value of adjusting brood sex ratio to the phenotype of the social mate. However, we found that the variation in effect sizes was unrelated to the proportion of extra‐pair paternity. Thus future studies should consider that mate quality dependent sex ratio adjustment may be driven by direct (material) rather than indirect (genetic) benefits. We also tested if the effect sizes are influenced by whether the focal male trait is indeed under sexual selection as it is assumed by the sex allocation theory. We found that for male traits with proven role in sexual selection, effect sizes significantly differed from the null expectation of random production of sons and daughters. For male traits with only presumed sexual role in sexual selection, the deviation from the null expectation was less convincing, and the effect sizes were significantly smaller. This result indicates that studies that neglect the assumptions of the hypotheses concerned, may lead to the underestimation of the mean effect size and, eventually, false conclusions.     

Behavioral,physiological, and morphological components of dominance and mate attraction in male green iguanas

This study investigated the morphological, physiological, and behavioral components of social dominance important for mate attraction in male green iguanas (Iguana iguana). A group of 9 male and 11 female adult green iguanas was studied in a large semi-natural enclosure during one reproductive season (October–January). Four of the nine males never initiated aggressive encounters; the other five were observed to display aggressively toward each other and were ranked in a linear dominance hierarchy. Head size was the most important factor influencing fighting success. Head size and display frequency were positively correlated with plasma testosterone levels. Dominance rank directly influenced ability to monopolize areas containing resources used by females. The quality of a male's home range, measured as his access to a large basking rock in the enclosure, was related to the proportion of potential mates found within his home range. One male greatly surpassed the others in his ability to defend a home range of high quality and attract potential mates. These data suggest that physiological and morphological factors, through their influence on social behavior, may ultimately affect male reproductive fitness. © 1992 Wiley-Liss, Inc.     

Copulation behaviour and paternity in shy albatrosses (Thalassarche cauta)

We investigated the mating system of shy albatrosses Thalassarche cauta by combining behavioural observations during the pre-laying period with genetic paternity analysis. Genetic data on the mating systems of several procellariiform seabirds have recently become available, but data on the reproductive behaviour of these species are rarely obtained. Our main aims were to describe the copulatory behaviour of this species and identify how males achieve within-pair and extra-pair paternity (EPP). Most copulations occurred on the nest, were unforced and were within-pair. Females controlled the success of copulations and were observed soliciting extra-pair matings. Within-pair and extra-pair copulations were behaviourally similar. A low frequency (7–10%, n =29 chicks) of EPP was detected despite male use of frequent copulation as a paternity guard. The pre-laying foraging exodus of female shy albatrosses differed from that in other albatrosses: it was relatively short in length, lasting c . 2 days, and within-pair copulations occurred after the female's return 2 days before laying. This may reflect the close proximity of feeding grounds to the breeding colony.     

Subordinate male meerkats prospect for extra-group paternity: alternative reproductive tactics in a cooperative mammal

In cooperatively breeding species, subordinates typically suffer strong constraints on within-group reproduction. While numerous studies have highlighted the additional fitness benefits that subordinates might accrue through helping, few have considered the possibility that subordinates may also seek extra-group matings to improve their chances of actually breeding. Here, we show that subordinate males in cooperative meerkat, Suricata suricatta, societies conduct frequent extraterritorial forays, during periods of peak female fertility, which give rise to matings with females in other groups. Genetic analyses reveal that extra-group paternity (EGP) accrued while prospecting contributes substantially to the reproductive success of subordinates: yielding the majority of their offspring (approx. 70%); significantly reducing their age at first reproduction and allowing them to breed without dispersing. We estimate that prospecting subordinates sire 20-25% of all young in the population. While recent studies on cooperative birds indicate that dominant males accrue the majority of EGP, our findings reveal that EGP can also arise from alternative reproductive tactics employed exclusively by subordinates. It is important, therefore, that future attempts to estimate the fitness of subordinate males in animal societies quantify the distribution of extra-group as well as within-group paternity, because a substantial proportion of the reproductive success of subordinates may otherwise go undetected.     

Explicit experimental evidence for the effectiveness of proximity as mate-guarding behaviour in reducing extra-pair fertilization in the Seychelles warbler

Extra-pair copulations (EPCs; copulations outside the pair bond) are widespread in birds and may result in extra-pair fertilizations (EPFs). To increase reproductive success, males should not only seek to gain EPFs, but also prevent their own females from gaining EPFs. Although males could reduce the number of EPCs by their mates, this does not necessarily mean that they reduce the number of EPFs; indeed several studies have found no association between EPCs and EPFs. Male Seychelles warblers (Acrocephalus sechellensis) follow their partner closely during the period when the pair female is most receptive (fertile period). We show that males that guarded their mates more closely were less likely to have extra-pair young in their nest. This study on the Seychelles warbler is the first to provide explicit experimental evidence that mate guarding is effective in reducing EPFs. First, in territories where free-living males were induced to stop mate guarding during the pair female's fertile period, extra-pair parentage was higher than in the control group. Second, in the experimental group, the probability of having an extra-pair nestling in the nest was positively associated with the number of days during the fertile period for which mate guarding was artificially stopped. Thus, male mate guarding was effective in reducing the risk of cuckoldry.     

Promiscuity, paternity and personality in the great tit

Understanding causes of variation in promiscuity within populations remain a major challenge. While most studies have focused on quantifying fitness costs and benefits of promiscuous behaviour, an alternative possibility--that variation in promiscuity within populations is maintained because of linkage with other traits-has received little attention. Here, we examine whether promiscuity in male and female great tits (Parus major)--quantified as extra-pair paternity (EPP) within and between nests--is associated with variation in a well-documented personality trait: exploration behaviour in a novel environment. Exploration behaviour has been shown to correlate with activity levels, risk-taking and boldness, and these are behaviours that may plausibly influence EPP. Exploration behaviour correlated positively with paternity gained outside the social pair among males in our population, but there was also a negative correlation with paternity in the social nest. Hence, while variation in male personality predicted the relative importance of paternity gain within and outside the pair bond, total paternity gained was unrelated to exploration behaviour. We found evidence that males paired with bold females were more likely to sire extra-pair young. Our data thus demonstrate a link between personality and promiscuity, with no net effects on reproductive success, suggesting personality-dependent mating tactics, in contrast with traditional adaptive explanations for promiscuity.     

杂色山雀的婚外父权与配偶间的遗传相容性无关

婚配制度作为一种进化稳定对策是动物对某一环境包括种群内部环境适应的结果。据统计,约92%的鸟类为社会性单配制,但单配制鸟类中很多都存在婚外父权现象,表现出社会性婚配制度与遗传性婚配制度的不一致性。杂色山雀(Parus varius)是一种社会性单配制的小型森林洞巢鸟,其是否存在婚外父权现象至今尚未见报道。通过对杂色山雀进行亲权鉴定以确定其有无婚外父权现象及婚外父权的比例,结果显示:45.45%(20/44)的巢存在婚外父权,14.39%(38/264)的后代为婚外子代,说明杂色山雀具有较高的婚外父权水平。进一步探究其婚外父权的发生原因,结果如下:(1)有、无婚外父权巢的社会性亲本之间的遗传相似性无显著差异(P=0.504);(2)有婚外父权巢中婚内子代和无婚外父权巢中子代的杂合度(P=0.118)以及有婚外父权巢中婚外子代与婚内子代的杂合度(P=0.206)均无显著差异。(3)有婚外父权巢中的婚内子代与婚外子代间8项体征指标比较,差异均不显著(Ps0.05)。综上,社会性单配制杂色山雀婚外父权的发生与配偶间的遗传相容性无关,还有待从其他角度进行探究。     

Low historical rates of cuckoldry in a Western European human population traced by Y-chromosome and genealogical data

Recent evidence suggests that seeking out extra-pair paternity (EPP) can be a viable alternative reproductive strategy for both males and females in many pair-bonded species, including humans. Accurate data on EPP rates in humans, however, are scant and mostly restricted to extant populations. Here, we provide the first large-scale, unbiased genetic study of historical EPP rates in a Western European human population based on combining Y-chromosomal data to infer genetic patrilineages with genealogical and surname data, which reflect known historical presumed paternity. Using two independent methods, we estimate that over the last few centuries, EPP rates in Flanders (Belgium) were only around 1–2% per generation. This figure is substantially lower than the 8–30% per generation reported in some behavioural studies on historical EPP rates, but comparable with the rates reported by other genetic studies of contemporary Western European populations. These results suggest that human EPP rates have not changed substantially during the last 400 years in Flanders and imply that legal genealogies rarely differ from the biological ones. This result has significant implications for a diverse set of fields, including human population genetics, historical demography, forensic science and human sociobiology.     

Repeatability of extra-pair mating in tree swallows

Models of sexual selection assume that female mating preferences are heritable and, thus, repeatable for individual females across multiple mating episodes. Previous studies of the repeatability of female preference have examined individuals in captivity and focused presumably on social mate choice. However, extra-pair mating is widespread and can also influence sexual selection. We examined the repeatability of extra-pair mating in a wild population of tree swallows (Tachycineta bicolor) by experimentally inducing females to lay two clutches in rapid succession within the same season. We found that the proportion of extra-pair young and the number of extra-pair sires were highly repeatable for individual females. However, the repeatability of specific extra-pair sires was low. We suggest that this unusual pattern of mating may be due to females maximizing the heterozygosity of their offspring.     

Natural and sexual selection against hybrid flycatchers

While sexual selection is generally assumed to quickly cause or strengthen prezygotic barriers between sister species, its role in causing postzygotic isolation, through the unattractiveness of intermediate hybrids, is less often examined. Combining 24 years of pedigree data and recently developed species-specific molecular markers from collared (Ficedula albicollis) and pied (Ficedula hypoleuca) flycatchers and their hybrids, we were able to quantify all key components of fitness. To disentangle the relative role of natural and sexual selection acting on F1 hybrid flycatchers, we estimated various fitness components, which when combined represent the total lifetime reproductive success of F1 hybrids, and then compared the different fitness components of F1 hybrids to that of collared flycatchers. Female hybrid flycatchers are sterile, with natural selection being the selective force involved, but male hybrids mainly experienced a reduction in fitness through sexual selection (decreased pairing success and increased rate of being cuckolded). To disentangle the role of sexual selection against male hybrids from a possible effect of genetic incompatibility (on the rate of being cuckolded), we compared male hybrids with pure-bred males expressing intermediate plumage characters. Given that sexual selection against male hybrids is a result of their intermediate plumage, we expect these two groups of males to have a similar fitness reduction. Alternatively, hybrids have reduced fitness owing to genetic incompatibility, in which case their fitness should be lower than that of the intermediate pure-bred males. We conclude that sexual selection against male hybrids accounts for approximately 75% of the reduction in their fitness. We discuss how natural and sexual selection against hybrids may have different implications for speciation and conclude that reinforcement of reproductive barriers may be more likely when there is sexual selection against hybrids.     

Multiyear multiple paternity and mate fidelity in the American alligator, Alligator mississippiensis

We examined multiple paternity during eight breeding events within a 10-year period (1995–2005) for a total of 114 wild American alligator nests in Rockefeller Wildlife Refuge in south-west Louisiana. Our goals included examining (i) within population variation in multiple paternity among years, (ii) variation in multiple paternity in individual females and (iii) the potential for mate fidelity. To accomplish this, in the current study, eggs were sampled from 92 nests over 6 years and analysed along with 22 nests from a previous 2-year study. Genotypes at five microsatellite loci were generated for 1802 alligator hatchlings. Multiple paternity was found in 51% of clutches and paternal contributions to these clutches were highly skewed. Rates of multiple paternity varied widely among years and were consistently higher in the current study than previously reported for the same population. Larger females have larger clutches, but are not more likely to have multiply sired nests. However, small females are unlikely to have clutches with more than two sires. For 10 females, nests from multiple years were examined. Seven (70%) of these females exhibited long-term mate fidelity, with one female mating with the same male in 1997, 2002 and 2005. Five females exhibiting partial mate fidelity (71%) had at least one multiple paternity nest and thus mated with the same male, but not exclusively. These patterns of mate fidelity suggest a potential role for mate choice in alligators.     

Size-related mating and mate guarding in the orb-web spiderNephila clavata (Araneae,Araneidae)

The orb-web spiderNephila clavata satisfies three conditions for assortative mating proposed by Ridley (The Explanation of Organic Diversity. The Comparative Method and Adaptations for Mating, Clarendon, Oxford, 1983); (1) a large male advantage in male-male competition, (2) a correlation between female size and fecundity, and (3) a long pairing duration. To test Ridley's hypothesis, size assortative mating and guarding were examined in the field. When data were pooled over time, assortative mating was found but this was due to temporal covariation of body sizes of males and receptive females. After controlling for the effect of time, size assortative guarding was not detected, although females guarded by males were larger than those not guarded in the early breeding season. Possible reasons for the absence of size assortative guarding were discussed.     

What is driving male mate preference evolution in Jamaican field crickets?

Male mating preferences are often a neglected aspect of studies on sexual selection. Male mating preferences may evolve if they provide males with direct‐fitness benefits such as increased opportunity to fertilize more eggs or indirect‐fitness benefits such as enhanced offspring survival. We tested these ideas using Jamaican field crickets, Gryllus assimilis, previously shown to exhibit male mating preferences. We randomly mated males to either their preferred or non‐preferred potential mates and then asked whether mating treatment influenced egg oviposition or offspring viability. Preferred females were not significantly more fecund and did not produce more viable eggs or offspring than non‐preferred females. Male mate preferences were therefore inconsistent with both the direct‐ and indirect‐fitness benefits hypotheses under the conditions of our experiment. Our null results leave us with an open question about what is driving the evolution of mating preferences in male crickets. Future research should explore the whether the offspring of preferred females are more attractive, have stronger immune systems, and/or experience higher adult longevity.     

Do male paternity guards ensure female fidelity in a duetting fairy-wren?

Most socially monogamous bird species engage in extra-pair mating,and consequently males may adopt various behavioral strategiesto guard paternity. However, the relationship between mate guardingand extra-pair paternity is unclear: low levels of extra-pairpaternity can be associated either with no mate guarding orwith intense mate guarding. We investigate paternity guardsin the purple-crowned fairy-wren (Malurus coronatus), a duettingspecies where extra-pair paternity is rare. This species isunusual in a genus known for extremely high levels of extra-pairmating. We examine the behavioral interactions between the sexesunderlying these low rates of extra-pair paternity and showthat male purple-crowned fairy-wrens do not use frequent copulationor courtship feeding to assure paternity or guard females acousticallyby duetting. Males maintain close proximity to females bothwhen they are fertile and when they are not breeding and donot invest in courtship displays to extra-pair females. Consistentwith predictions of theoretical models, low extra-pair paternityin this species may be related to female fidelity rather thanmale paternity assurance strategies, but short-term removalof males would be necessary to test this experimentally.     

How female reed buntings benefit from extra-pair mating behaviour: testing hypotheses through patterns of paternity in sequential broods

Extra-pair paternity is an important aspect of reproductive strategies in many species of birds. Given that in most species females control whether fertilization occurs, they are expected to benefit in some way from the extra-pair matings. In this study we use patterns of extra-pair paternity (EPP) in broods of individual reed buntings (Emberiza schoeniclus), both within and between seasons, to test four hypothesized female benefits: (1) assessing potential future partners and seeking (2) genetic diversity (3) good genes, or (4) compatible genes. Reed buntings are socially monogamous, multibrooded passerines with extremely high levels of extra-pair paternity. We studied a population of reed buntings in the Netherlands in 2002 and 2003; 51% of offspring in 74% of nests were extra-pair. We showed that patterns of EPP did not support the first and second hypotheses, since females did not form a pair with previous extra-pair partners, EPP was not evenly distributed among broods and more broods than expected were sired by a single male. Furthermore, there was no relation between a male's within- and extra-pair fertilization success, no consistency in EPP between breeding attempts, no effect of parental relatedness on EPP and several cases of reciprocal paternity. These patterns do not support the good genes hypothesis and are most consistent with the genetic compatibility hypothesis. However, our previous finding that older males are more successful in gaining EPP, suggests some effect of good genes. These hypotheses need not be mutually exclusive, as females may select compatible males above a certain quality threshold (e.g. old males).