Female mating preferences and offspring survival: testing hypotheses on the genetic basis of mate choice in a wild lekking bird

Asymmetric Male Mating Success in Lek-Breeding Rhinella arenarum

Mate choice is the attempt of an individual to gain higher reproductive fitness by preferring to mate with some individuals and not with others. We studied the role of mate choice in the mating system of the neotropical toad Rhinella arenarum by assessing male reproductive tactics for mate acquisition and the contribution of female choice for pair formation. In a shallow pond in central Argentina, we estimated male mating success and the corresponding reproductive tactics by focal observation. The variation of phenotypic and genotypic traits (size and shape, longevity, vocalization features, heterozygosity) was related to the observed mating success in 110 males. The phonotactic response of 21 reproductive females to conspecific advertisement call features was tested in arena experiments. Mating success was limited to 32 males, pair formation was size-assortative. The dominant reproductive tactics were advertising from call positions near suitable breeding sites and pre-mating fights with intruding males, whereas the interception of amplectant pairs and the displacement of mated males were never observed. Female phonotaxis was directed to conspecific choruses but complex and simple call structures were not distinguished. We conclude that the mating system is a lek combining pre-mating fights among males and female choice of slightly smaller males. Fights interfere with female choice, undermining size-assortative mating. This is a unique system in the R. marina species group, in which interception behavior dominates reproduction.

A reexamination of theoretical arguments that indirect selection on mate preference is likely to be weaker than direct selection

Female preference for male ornaments or displays can evolve by indirect selection resulting from genetic benefits of mate choices, or by direct selection resulting from nongenetic benefits or selection on sensory systems occurring in other contexts. In an influential paper, Kirkpatrick and Barton used a good-genes model and evolutionary rates estimated from the fossil record to conclude that indirect selection on preference is likely to be weak compared to typical strengths of direct selection. More recent authors have extrapolated from Kirkpatrick and Barton's conclusions to suggest that the presence of preference-trait genetic correlations in equations for indirect but not direct selection gives a purely theoretical basis to the conclusion that the former is likely to be weaker than the latter. Here, I challenge these views, and argue that the relative importance of direct and indirect selection on preference is an empirical issue that defies simple generalizations. First, I show that Kirkpatrick and Barton based their conclusion on a questionable claim about typical rates of evolution due to direct selection. Second, I argue that claiming that direct selection on preference is stronger than indirect selection because only equations for the latter contain a genetic correlation mistakes the mathematical simplicity with which direct selection is usually represented for evidence regarding its magnitude. By comparing a simple equation for the selection response of preference caused by somatic ("direct") benefits to Kirkpatrick and Barton's result for the response to indirect selection, I show that indirect selection on preference is not inherently weaker than direct selection. I also point out an important but overlooked reason why selection on preference under the sensory bias hypothesis can be expected to be less effective in the long run than that from either somatic or genetic benefits of mate choices.

Olfactory camouflage and communication in birds

Smell is a sensory modality that is rarely considered in birds, but evidence is mounting that olfaction is an important aspect of avian behaviour and ecology. The uropygial gland produces an odoriferous secretion (preen oil) that can differ seasonally and between the sexes. These differences are hypothesized to function in olfactory camouflage, i.e. minimizing detection by nest predators (olfactory crypsis hypothesis), and/or intraspecific olfactory communication, particularly during breeding (sex semiochemical hypothesis). However, evidence for seasonal and sex differences in preen oil is mixed, with some studies finding differences and others not, and direct evidence for the putative function(s) of seasonal variation and sex differences in preen oil remains limited. We conducted a systematic review of the evidence for such changes in preen oil chemical composition, finding seasonal differences in 95% of species (57/60 species in 35 studies) and sex differences in 47% of species (28/59 species in 46 studies). We then conducted phylogenetic comparative analyses using data from 59 bird species to evaluate evidence for both the olfactory crypsis and sex semiochemical hypotheses. Seasonal differences were more likely in the incubating than non-incubating sex in ground-nesting species, but were equally likely regardless of incubation strategy in non-ground-nesting species. This result supports the olfactory crypsis hypothesis, if ground nesters are more vulnerable to olfactorily searching predators than non-ground nesters. Sex differences were more likely in species with uniparental than biparental incubation and during breeding than non-breeding, consistent with both the olfactory crypsis and sex semiochemical hypotheses. At present, the data do not allow us to disentangle these two hypotheses, but we provide recommendations that will enable researchers to do so.

Inbreeding Coefficient and Distance in MHC Genes of Parents as Predictors of Reproductive Success in Domestic Cat

Simple Summary

Inbreeding and low diversity in MHC (major histocompatibility complex) genes can have a significant impact on the survival and quality of offspring in mammals. At the same time, a decrease in genetic diversity can be disastrous for animals at individual and species level. For felines, studies of the effects of inbreeding and low variety in MHC genes are conducted on populations with a low number of animals, where there is a high probability of a shortage of available partners, and, accordingly, their choice. The use of model species, especially domestic cats, allows us to identify the main consequences of inbreeding and the lack of a choice of partners for future offspring. The survival of offspring in a domestic cat is primarily affected by the degree of similarity/difference in the genes of the parents’ MHC. Parents with the maximum distance in MHC genes have a larger proportion of surviving kittens, and this effect is most pronounced immediately after birth. In parents with the minimum distance in MHC genes, a significant percentage of kittens are either stillborn or die on the first day after birth. However, inbreeding and the similarity of parents in MHC genes in domestic cats did not affect the body mass of kittens.

Abstract

Inbreeding and low diversity in MHC genes are considered to have a negative effect on reproductive success in animals. This study presents an analysis of the number and body mass of offspring in domestic cat, depending on the inbreeding coefficient and the degree of similarity in MHC genes of class I and II in parents. Inbred partners had a lower number of live kittens at birth than outbred ones. At the same time, the inbreeding coefficient did not affect the litter size and the number of offspring who survived until the period of transition to solid food. The most significant predictor for the number of surviving offspring was the degree of parental similarity in MHC genes: the parents with the maximum distance in MHC genes had more survived kittens. Moreover, this effect was most pronounced immediately after birth. A significant percentage of kittens from parents with a minimum distance in MHC genes were either stillborn or died on the first day after birth. By the age of transition to solid food, this effect is no longer so pronounced. Furthermore, neither the inbreeding coefficient nor the distance in MHC genes of parents had any effect on the body mass of kittens.

Evaluating the existence and benefit of major histocompatibility complex-based mate choice in an isolated owl population

How mate preferences evolve in the first place has been a major conundrum for sexual selection. Some hypotheses explaining this assume fitness benefit derived from subsequent generations. Major histocompatibility complex (MHC)-based mate choice is a representative example of the mate choice that is associated with such trans-generational mechanisms. To provide evidences for fitness benefit of MHC-based mate choice, previous studies assessed the association between own MHC genotype and own fitness components. However, the association between MHC-based mate choice in the parental generation and fitness components in the resultant offspring generation has only rarely been measured in wild populations. Focusing on the isolated population of the monogamous Ryukyu Scops Owl (Otus elegans interpositus) on Minami-daito Island, Japan, we found evidence of MHC-based mate choice. However, we found no evidence of MHC-based mate choice increasing own reproductive success or offspring survival. This is a rare case study that directly examines the existence of the trans-generational indirect benefit of MHC-based mate choice for genetic compatibility from trans-generational data in a wild bird population. By investigating the fitness benefits of mate choice, this study serves to facilitate our understanding of the evolution of MHC-based mate choice.

Female choice for related males in wild red-backed toadlets (Pseudophryne coriacea)

Mate choice for genetic benefits is assumed to be widespread in nature, yet very few studies have comprehensively examined relationships between female mate choice and male genetic quality in wild populations. Here, we use exhaustive sampling and single nucleotide polymorphisms to provide a partial test of the “good genes as heterozygosity” hypothesis and the “genetic compatibility” hypothesis in an entire population of terrestrial breeding red-backed toadlets, Pseudophryne coriacea. We found that successful males did not display higher heterozygosity, despite a positive relationship between male heterozygosity and offspring heterozygosity. Rather, in the larger of 2 breeding events, we found that successful males were more genetically similar to their mate than expected under random mating, indicating that females can use pre- or post-copulatory mate choice mechanisms to bias paternity toward more related males. These findings provide no support for the good genes as heterozygosity hypothesis but lend support to the genetic compatibility hypothesis. A complete test of this hypothesis will now require evaluating how parental genetic similarity impacts offspring fitness. Terrestrial toadlets show a high degree of site fidelity, high levels of genetic structuring between populations, and frequently hybridize with sister species. As such, female mate choice for related males may be an adaptive strategy to reduce outbreeding depression. Our findings provide the first population-wide evidence for non-random preferential inbreeding in a wild amphibian. We argue that such reproductive patterns may be common in amphibians because extreme genetic differentiation within meta-populations creates an inherently high risk of outbreeding depression.

Male vocalizations convey information on kinship and inbreeding in a lekking bird

Kinship and inbreeding are two major components involved in sexual selection and mating system evolution. However, the mechanisms underlying recognition and discrimination of genetically related or inbred individuals remain unclear. We investigated whether kinship and inbreeding information is related to low-frequency vocalizations, "booms," produced by males during their courtship in the lekking houbara bustard (Chlamydotis undulata undulata). Based on a captive breeding program where the pedigree of all males is known, we investigated the similarity of booms' acoustic parameters among captive males more or less individually inbred and therefore genetically related with each other. In the wild, we investigated the relationship between the spatial distribution of males within leks and the similarity of acoustic parameters of their booms. In the captive population, we found (a) a relationship between the individual inbreeding level of captive males and their vocalization parameters; (b) that kin share similar frequency and temporal characteristics of their vocalizations. In the wild, we found no evidence for spatial structuring of males based on their acoustic parameters, in agreement with previous genetic findings on the absence of kin association within houbara bustard leks. Overall, our results indicate that genetic information potentially related to both the identity and quality of males is contained in their vocalizations.

Mate choice explains high genetic diversity in a small founding population of the New Zealand sea lion (Phocarctos hookeri)

Founder populations are susceptible to reduced genetic diversity, which can hinder successful population establishment. A new genetic lineage of the New Zealand sea lion (Phocarctos hookeri) has recently colonised the historical range of the New Zealand mainland (Otago Peninsula). Despite a small founding population, previous research indicated that nuclear genetic diversity in the Otago Peninsula population is similar to that of the larger source population (Sandy Bay, Auckland Islands). Our research aimed to identify whether mechanisms of female mate choice could help to explain the unexpectedly high level of genetic diversity in the founder population. We used genetic data at 12 microsatellite loci for mother–pup pairs from both populations, and the software COLONY to identify putative paternal genotypes inferred from allele sharing between known mother–pup pairs. We found that mating pairs were, on average, more related at the Otago Peninsula location. However, Sandy Bay females were mating with males more related to themselves than expected by chance, while the Otago Peninsula females were not. These findings suggest that female choice in this otariid species appears important, although may be constrained in some situations. Our findings also help to explain how the recently founded population is able to maintain a viable, growing population.

Generalized structural equations improve sexual-selection analyses

Sexual selection is an intense evolutionary force, which operates through competition for the access to breeding resources. There are many cases where male copulatory success is highly asymmetric, and few males are able to sire most females. Two main hypotheses were proposed to explain this asymmetry: "female choice" and "male dominance". The literature reports contrasting results. This variability may reflect actual differences among studied populations, but it may also be generated by methodological differences and statistical shortcomings in data analysis. A review of the statistical methods used so far in lek studies, shows a prevalence of Linear Models (LM) and Generalized Linear Models (GLM) which may be affected by problems in inferring cause-effect relationships; multi-collinearity among explanatory variables and erroneous handling of non-normal and non-continuous distributions of the response variable. In lek breeding, selective pressure is maximal, because large numbers of males and females congregate in small arenas. We used a dataset on lekking fallow deer (Dama dama), to contrast the methods and procedures employed so far, and we propose a novel approach based on Generalized Structural Equations Models (GSEMs). GSEMs combine the power and flexibility of both SEM and GLM in a unified modeling framework. We showed that LMs fail to identify several important predictors of male copulatory success and yields very imprecise parameter estimates. Minor variations in data transformation yield wide changes in results and the method appears unreliable. GLMs improved the analysis, but GSEMs provided better results, because the use of latent variables decreases the impact of measurement errors. Using GSEMs, we were able to test contrasting hypotheses and calculate both direct and indirect effects, and we reached a high precision of the estimates, which implies a high predictive ability. In synthesis, we recommend the use of GSEMs in studies on lekking behaviour, and we provide guidelines to implement these models.

No speed dating please! Patterns of social preference in male and female house mice

BACKGROUND

In many animal species, interactions between individuals of different sex often occur in the context of courtship and mating. During these interactions, a specific mating partner can be chosen. By discriminating potential mates according to specific characteristics, individuals can increase their evolutionary fitness in terms of reproduction and offspring survival. In this study, we monitored the partner preference behaviour of female and male wild house mice (Mus musculus domesticus) from populations in Germany (G) and France (F) in a controlled cage setup for 5 days and six nights. We analysed the effects of individual factors (e.g. population origin and sex) on the strength of preference (selectivity), as well as dyadic factors (e.g. neutral genetic distance and major histocompatibility complex (MHC) dissimilarity) that direct partner preferences.

RESULTS

Selectivity was stronger in mice with a pure population background than mixed individuals. Furthermore, female mice with a father from the German population had stronger selectivity than other mice. In this group, we found a preference for partners with a larger dissimilarity of their father's and their partner's MHC, as assessed by sequencing the H2-Eß locus. In all mice, selectivity followed a clear temporal pattern: it was low in the beginning and reached its maximum only after a whole day in the experiment. After two days, mice seemed to have chosen their preferred partner, as this choice was stable for the remaining four days in the experiment.

CONCLUSIONS

Our study supports earlier findings that mate choice behaviour in wild mice can be paternally influenced. In our study, preference seems to be potentially associated with paternal MHC distance. To explain this, we propose familial imprinting as the most probable process for information transfer from father to offspring during the offspring's early phase of life, which possibly influences its future partner preferences. Furthermore, our experiments show that preferences can change after the first day of encounter, which implies that extended observation times might be required to obtain results that allow a valid ecological interpretation.

Polymorphism in the major histocompatibility complex (MHC class II B) genes of the Rufous-backed Bunting (Emberiza jankowskii)

Genetic diversity is one of the pillars of conservation biology research. High genetic diversity and abundant genetic variation in an organism may be suggestive of capacity to adapt to various environmental changes. The major histocompatibility complex (MHC) is known to be highly polymorphic and plays an important role in immune function. It is also considered an ideal model system to investigate genetic diversity in wildlife populations. The Rufous-backed Bunting (Emberiza jankowskii) is an endangered species that has experienced a sharp decline in both population and habitat size. Many historically significant populations are no longer present in previously populated regions, with only three breeding populations present in Inner Mongolia (i.e., the Aolunhua, Gahaitu and Lubei557 populations). Efforts focused on facilitating the conservation of the Rufous-backed Bunting (Emberiza jankowskii) are becoming increasingly important. However, the genetic diversity of E. jankowskii has not been investigated. In the present study, polymorphism in exon 2 of the MHCIIB of E. jankowskii was investigated. This polymorphism was subsequently compared with a related species, the Meadow Bunting (Emberiza cioides). A total of 1.59 alleles/individual were detected in E. jankowskii and 1.73 alleles/individual were identified in E. cioides. The maximum number of alleles per individual from the three E. jankowskii populations suggest the existence of at least three functional loci, while the maximum number of alleles per individual from the three E. cioides populations suggest the presence of at least four functional loci. Two of the alleles were shared between the E. jankowskii and E. cioides. Among the 12 unique alleles identified in E. jankowskii, 10.17 segregating sites per allele were detected, and the nucleotide diversity was 0.1865. Among the 17 unique alleles identified in E. cioides, eight segregating sites per allele were detected, and the nucleotide diversity was 0.1667. Overall, compared to other passerine birds, a relatively low level of MHC polymorphism was revealed in E. jankowskii, which was similar to that in E. cioides. Positive selection was detected by PAML/SLAC/FEL analyses in the region encoding the peptide-binding region in both species, and no recombination was detected. Phylogenetic analysis showed that the alleles from E. jankowskii and E. cioides belong to the same clade and the two species shared similar alleles, suggesting the occurrence of a trans-species polymorphism between the two Emberiza species.

Genetic variation in male attractiveness: It is time to see the forest for the trees

Female choice based on multiple male traits, rather than on any single one, has been reported in many species and may well be a rule rather than an exception. However, the implications this has for selection acting on choosiness itself remain underappreciated. We argue that this constitutes one of the important impediments to our understanding of the evolution of mate choice. We discuss this issue primarily in the context of the Fisherian model of sexual selection. We review theory and empirical data, showing how the crucial parameter of the model-genetic variation in male attractiveness-can be estimated when attractiveness is a function of multiple traits. Based on the reviewed theory, we show how relying on individual male traits, instead of overall attractiveness, can produce biased estimates of Fisherian benefits of female choice. This bias can be substantial, especially when many traits contribute to male attractiveness. We discuss a number of methodological issues that, we hope, will stimulate future studies and help resolving the long-standing mystery of mate choice.

Heterozygosity-fitness correlations in a wild mammal population: accounting for parental and environmental effects

HFCs (heterozygosity–fitness correlations) measure the direct relationship between an individual's genetic diversity and fitness. The effects of parental heterozygosity and the environment on HFCs are currently under-researched. We investigated these in a high-density U.K. population of European badgers (Meles meles), using a multimodel capture–mark–recapture framework and 35 microsatellite loci. We detected interannual variation in first-year, but not adult, survival probability. Adult females had higher annual survival probabilities than adult males. Cubs with more heterozygous fathers had higher first-year survival, but only in wetter summers; there was no relationship with individual or maternal heterozygosity. Moist soil conditions enhance badger food supply (earthworms), improving survival. In dryer years, higher indiscriminate mortality rates appear to mask differential heterozygosity-related survival effects. This paternal interaction was significant in the most supported model; however, the model-averaged estimate had a relative importance of 0.50 and overlapped zero slightly. First-year survival probabilities were not correlated with the inbreeding coefficient (f); however, small sample sizes limited the power to detect inbreeding depression. Correlations between individual heterozygosity and inbreeding were weak, in line with published meta-analyses showing that HFCs tend to be weak. We found support for general rather than local heterozygosity effects on first-year survival probability, and g2 indicated that our markers had power to detect inbreeding. We emphasize the importance of assessing how environmental stressors can influence the magnitude and direction of HFCs and of considering how parental genetic diversity can affect fitness-related traits, which could play an important role in the evolution of mate choice.

Differential allocation in a lekking bird: females lay larger eggs and are more likely to have male chicks when they mate with less related males

The differential allocation hypothesis predicts increased investment in offspring when females mate with high-quality males. Few studies have tested whether investment varies with mate relatedness, despite evidence that non-additive gene action influences mate and offspring genetic quality. We tested whether female lekking lance-tailed manakins (Chiroxiphia lanceolata) adjust offspring sex and egg volume in response to mate attractiveness (annual reproductive success, ARS), heterozygosity and relatedness. Across 968 offspring, the probability of being male decreased with increasing parental relatedness but not father ARS or heterozygosity. This correlation tended to diminish with increasing lay-date. Across 162 offspring, egg volume correlated negatively with parental relatedness and varied with lay-date, but was unrelated to father ARS or heterozygosity. Offspring sex and egg size were unrelated to maternal age. Comparisons of maternal half-siblings in broods with no mortality produced similar results, indicating differential allocation rather than covariation between female quality and relatedness or sex-specific inbreeding depression in survival. As males suffer greater inbreeding depression, overproducing females after mating with related males may reduce fitness costs of inbreeding in a system with no inbreeding avoidance, while biasing the sex of outbred offspring towards males may maximize fitness via increased mating success of outbred sons.