Smell throughout the life course

The sense of smell is an important mediator of health and sociality at all stages of life, yet it has received limited attention in our lineage. Olfaction starts in utero and participates in the establishment of social bonds in children, and of romantic and sexual relationships after puberty. Smell further plays a key role in food assessment and danger avoidance; in modern societies, it also guides our consumer behavior. Sensory abilities typically decrease with age and can be impacted by diseases, with repercussions on health and well-being. Here, we critically review our current understanding of human olfactory communication to refute outdated notions that our sense of smell is of low importance. We provide a summary of the biology of olfaction, give a prospective overview of the importance of the sense of smell throughout the life course, and conclude with an outline of the limitations and future directions in this field.

Host-parasite coevolution and the stability of genetic kin recognition

Crozier's paradox suggests that genetic kin recognition will not be evolutionarily stable. The problem is that more common tags (markers) are more likely to be recognized and helped. This causes common tags to increase in frequency, eliminating the genetic variability that is required for genetic kin recognition. Two potential solutions to this problem have been suggested: host-parasite coevolution and multiple social encounters. We show that the host-parasite coevolution hypothesis does not work as commonly assumed. Host-parasite coevolution only stabilizes kin recognition at a parasite resistance locus if parasites adapt rapidly to hosts and cause intermediate or high levels of damage (virulence). Additionally, when kin recognition is stabilized at a parasite resistance locus, this can have an additional cost of making hosts more susceptible to parasites. However, we show that if the genetic architecture is allowed to evolve, meaning natural selection can choose the recognition locus, genetic kin recognition is more likely to be stable. The reason for this is that host-parasite coevolution can maintain tag diversity at another (neutral) locus by genetic hitchhiking, allowing that other locus to be used for genetic kin recognition. These results suggest a way that host-parasite coevolution can resolve Crozier's paradox, without making hosts more susceptible to parasites. However, the opportunity for multiple social encounters may provide a more robust resolution of Crozier's paradox.

Social complexity as a driving force of gut microbiota exchange among conspecific hosts in non-human primates

The emergent concept of the social microbiome implies a view of a highly connected biological world, in which microbial interchange across organisms may be influenced by social and ecological connections occurring at different levels of biological organization. We explore this idea reviewing evidence of whether increasing social complexity in primate societies is associated with both higher diversity and greater similarity in the composition of the gut microbiota. By proposing a series of predictions regarding such relationship, we evaluate the existence of a link between gut microbiota and primate social behavior. Overall, we find that enough empirical evidence already supports these predictions. Nonetheless, we conclude that studies with the necessary, sufficient, explicit, and available evidence are still scarce. Therefore, we reflect on the benefit of founding future analyses on the utility of social complexity as a theoretical framework.

Feather chemicals contain information about the major histocompatibility complex in a highly scented seabird

Mate choice informed by the immune genes of the major histocompatibility complex (MHC) may provide fitness benefits including offspring with increased immunocompetence. Olfactory cues are considered the primary mechanism organisms use to evaluate the MHC of potential mates, yet this idea has received limited attention in birds. Motivated by a finding of MHC-dependent mate choice in the Leach's storm-petrel (Oceanodroma leucorhoa), we examined whether the chemical profiles of this highly scented seabird contain information about MHC genes. Whereas previous studies in birds examined non-volatile compounds, we used gas chromatography-mass spectrometry to measure the volatile compounds emitted from feathers that potentially serve as olfactory infochemicals about MHC and coupled this with locus-specific genotyping of MHC IIB genes. We found that feather chemicals reflected individual MHC diversity through interactions with sex and breeding status. Furthermore, similarity in MHC genotype was correlated with similarity in chemical profiles within female-female and male-female dyads. We provide the first evidence that volatile chemicals from bird feathers can encode information about the MHC. Our findings suggest that olfaction likely aids MHC-based mate choice in this species and highlight a role for chemicals in mediating genetic mate choice in birds where this mode of communication has been largely overlooked.

Selection and demography drive range-wide patterns of MHC-DRB variation in mule deer

BACKGROUND

Standing genetic variation is important especially in immune response-related genes because of threats to wild populations like the emergence of novel pathogens. Genetic variation at the major histocompatibility complex (MHC), which is crucial in activating the adaptive immune response, is influenced by both natural selection and historical population demography, and their relative roles can be difficult to disentangle. To provide insight into the influences of natural selection and demography on MHC evolution in large populations, we analyzed geographic patterns of variation at the MHC class II DRB exon 2 locus in mule deer (Odocoileus hemionus) using sequence data collected across their entire broad range.

RESULTS

We identified 31 new MHC-DRB alleles which were phylogenetically similar to other cervid MHC alleles, and one allele that was shared with white-tailed deer (Odocoileus virginianus). We found evidence for selection on the MHC including high dN/dS ratios, positive neutrality tests, deviations from Hardy-Weinberg Equilibrium (HWE) and a stronger pattern of isolation-by-distance (IBD) than expected under neutrality. Historical demography also shaped variation at the MHC, as indicated by similar spatial patterns of variation between MHC and microsatellite loci and a lack of association between genetic variation at either locus type and environmental variables.

CONCLUSIONS

Our results show that both natural selection and historical demography are important drivers in the evolution of the MHC in mule deer and work together to shape functional variation and the evolution of the adaptive immune response in large, well-connected populations.

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.

The attraction trick: males in early stages of disease become more chemically attractive to Nile tilapia (Oreochromis niloticus) females

In aquatic systems, olfaction plays an important role in acquiring information about the social environment and influences important behaviours in various contexts, including predator avoidance, foraging, aggressive and reproductive behaviour and mate selection. As the presence of diseases might modify individual odour, fish may use the variability in conspecifics' odours as an indicator of the health status and infectious load of potential mates. Here, female Nile tilapia were tested for their ability to detect infected males and discriminate between bacterial infected and uninfected individuals by means of chemical cues. Females were allowed to choose between the odours of males infected by Aeromonas hydrophila bacteria and uninfected males. The findings show that female Nile tilapia initially showed a preference for infected males in terms of their first choice in a dichotomous choice test, but the total duration of time spent with the stimulus from infected males was not longer than that for the uninfected males. This may indicate that males at early stages of infection, i.e., without advanced clinical signs of infection, emit odours that allow them to enjoy the benefits of socialization when the infection is not yet detected by conspecifics. Thus, in the context of reproduction, males might attract female partners and have some chance of reproducing, before being avoided.

Genetic effects of long-term captive breeding on the endangered pygmy hog

Long-term captive populations often accumulate genetic changes that are detrimental to their survival in the wild. Periodic genetic evaluation of captive populations is thus necessary to identify deleterious changes and minimize their impact through planned breeding. Pygmy hog (Porcula salvania) is an endangered species with a small population inhabiting the tall sub-Himalayan grasslands of Assam, India. A conservation breeding program of pygmy hog from six founders has produced a multi-generational captive population destined for reintroduction into the wild. However, the impact of conservation breeding on its genetic diversity remained undocumented. Here, we evaluate temporal genetic changes in 39 pygmy hogs from eight consecutive generations of a captive population using genome-wide SNPs, mitochondrial genomes, and MHC sequences, and explore the relationship between genetic diversity and reproductive success. We find that pygmy hog harbors a very low genome-wide heterozygosity (H) compared to other members of the Suidae family. However, within the captive population we find excess heterozygosity and a significant increase in H from the wild-caught founders to the individuals in subsequent generations due to the selective pairing strategy. The MHC and mitochondrial nucleotide diversities were lower in captive generations compared to the founders with a high prevalence of low-frequency MHC haplotypes and more unique mitochondrial genomes. Further, even though no signs of genetic inbreeding were observed from the estimates of individual inbreeding coefficient F and between individuals (F_IS) in each generation, the kinship coefficient showed a slightly increasing trend in the recent generations, due to a relatively smaller non-random sample size compared to the entire captive population. Surprisingly, male pygmy hogs that had higher heterozygosity also showed lower breeding success. We briefly discuss the implications of our findings in the context of breeding management and recommend steps to minimize the genetic effects of long-term captive breeding.

Preen gland microbiota covary with major histocompatibility complex genotype in a songbird

Pathogen-mediated selection at the major histocompatibility complex (MHC) is thought to promote MHC-based mate choice in vertebrates. Mounting evidence implicates odour in conveying MHC genotype, but the underlying mechanisms remain uncertain. MHC effects on odour may be mediated by odour-producing symbiotic microbes whose community structure is shaped by MHC genotype. In birds, preen oil is a primary source of body odour and similarity at MHC predicts similarity in preen oil composition. Hypothesizing that this relationship is mediated by symbiotic microbes, we characterized MHC genotype, preen gland microbial communities and preen oil chemistry of song sparrows (Melospiza melodia). Consistent with the microbial mediation hypothesis, pairwise similarity at MHC predicted similarity in preen gland microbiota. Counter to this hypothesis, overall microbial similarity did not predict chemical similarity of preen oil. However, permutation testing identified a maximally predictive set of microbial taxa that best reflect MHC genotype, and another set of taxa that best predict preen oil chemical composition. The relative strengths of relationships between MHC and microbes, microbes and preen oil, and MHC and preen oil suggest that MHC may affect host odour both directly and indirectly. Thus, birds may assess MHC genotypes based on both host-associated and microbially mediated odours.

Electrophysiological Recordings from the Olfactory Epithelium and Human Brain in Response to Stimulation with HLA Related Peptides

In many species, social communication and mate choice are influenced by olfactory cues associated with the major histocompatibility complex (MHC). It has been reported that humans also respond to olfactory signals related to the human MHC-equivalent, the Human Leucocyte Antigen (HLA)-System, and exhibit an olfactory-mediated preference for potential mating partners with a dissimilar, disassortative, HLA-type compared to their own. The aim of this study was to investigate whether HLA-associated peptides, presented as volatile cues, elicit neuronal responses at the receptors in the human olfactory epithelium and can be consciously perceived. To this end the discrimination ability for peptides was tested in a 3-alternative forced choice model. Furthermore electro-olfactograms of the olfactory epithelium and EEG-derived chemosensory event related potentials were recorded using precisely controlled olfactometric stimulation with peptides and control odors. Based on responses from 52 young, healthy participants the peptides could not be discriminated and the electrophysiological signals provided no evidence for a specific response to the peptides which was in contrast to the control odors. In conclusion, within the current setup the results suggest that HLA-associated peptides do not produce specific olfactory activation in humans.

Males perceive honest information from female released sex pheromone in a moth

There is accumulating evidence that male insects advertise their quality to conspecific females through pheromones. However, most studies of female released sex pheromone assume information transfer regarding merely the species of the female and her mating status. We show that more information is conveyed through the female sex pheromone, positioning it as an honest sexual trait. We demonstrate that females in bad physical conditions (small, starved, or old) lay significantly fewer eggs than females in good conditions (large, fed, or young). The ratio of components in the sex pheromone blend in gland extracts of the female pink bollworm moths provided honest information on most of the phenotypic conditions tested, whereas the pheromone amount in the glands provided an honest signal of quality for extreme phenotypes only. Moreover, males used the information conveyed by the female pheromone to choose their mates, approaching females that signaled higher reproductive potential. In addition, when simulating the female effect, using the synthetic pheromone blend that represents higher quality females (0.6:0.4 ZZ:ZE), more males were attracted to this blend than to the blend representing the population mean (0.5:0.5 ZZ:ZE). Both, female advertisement for males and the male choosiness, suggest that pheromones have evolved as sexual traits under directional, sexual selection. We suggest that the pheromone blend may serve as a multicomponent signal whereby each component adds information concerning the current condition of the female, and all are necessary to elicit a mate searching response.

Meta-analytic evidence that animals rarely avoid inbreeding

Animals are usually expected to avoid mating with relatives (kin avoidance) as incestuous mating can lead to the expression of inbreeding depression. Yet, theoretical models predict that unbiased mating with regards to kinship should be common, and that under some conditions, the inclusive fitness benefits associated with inbreeding can even lead to a preference for mating with kin. This mismatch between empirical and theoretical expectations generates uncertainty as to the prevalence of inbreeding avoidance in animals. Here, we synthesized 677 effect sizes from 139 experimental studies of mate choice for kin versus non-kin in diploid animals, representing 40 years of research, using a meta-analytical approach. Our meta-analysis revealed little support for the widely held view that animals avoid mating with kin, despite clear evidence of publication bias. Instead, unbiased mating with regards to kinship appears widespread across animals and experimental conditions. The significance of a variety of moderators was explored using meta-regressions, revealing that the degree of relatedness and prior experience with kin explained some variation in the effect sizes. Yet, we found no difference in kin avoidance between males and females, choice and no-choice experiments, mated and virgin animals or between humans and animals. Our findings highlight the need to rethink the widely held view that inbreeding avoidance is a given in experimental studies.

Host Genetic Diversity and Infectious Diseases. Focus on Wild Boar, Red Deer and Tuberculosis

Host genetic diversity tends to limit disease spread in nature and buffers populations against epidemics. Genetic diversity in wildlife is expected to receive increasing attention in contexts related to disease transmission and human health. Ungulates such as wild boar (Sus scrofa) and red deer (Cervus elaphus) are important zoonotic hosts that can be precursors to disease emergence and spread in humans. Tuberculosis is a zoonotic disease with relevant consequences and can present high prevalence in wild boar and red deer populations. Here, we review studies on the genetic diversity of ungulates and determine to what extent these studies consider its importance on the spread of disease. This assessment also focused on wild boar, red deer, and tuberculosis. We found a disconnection between studies treating genetic diversity and those dealing with infectious diseases. Contrarily, genetic diversity studies in ungulates are mainly concerned with conservation. Despite the existing disconnection between studies on genetic diversity and studies on disease emergence and spread, the knowledge gathered in each discipline can be applied to the other. The bidirectional applications are illustrated in wild boar and red deer populations from Spain, where TB is an important threat for wildlife, livestock, and humans.

Patterns of MHC-dependent sexual selection in a free-living population of sheep

The MHC is one of the most polymorphic gene clusters in vertebrates and play an essential role in adaptive immunity. Apart from pathogen-mediated selection, sexual selection can also contribute to the maintenance of MHC diversity. MHC-dependent sexual selection could occur via several mechanisms but at present there is no consensus as to which of these mechanisms are involved and their importance. Previous studies have often suffered from limited genetic and behavioural data and small sample size, and were rarely able to examine all the mechanisms together, determine whether signatures of MHC-based non-random mating are independent of genomic effects or differentiate whether MHC-dependent sexual selection takes place at the pre- or post-copulatory stage. In this study, we use Monte Carlo simulation to investigate evidence for non-random MHC-dependent mating patterns by all three mechanisms in a free-living population of Soay sheep. Using 1710 sheep diplotyped at the MHC class IIa region and genome-wide SNPs, together with field observations of consorts, we found sexual selection against a particular haplotype in males at the pre-copulatory stage and sexual selection against female MHC heterozygosity during the rut. We also found MHC-dependent disassortative mating at the post-copulatory stage, along with strong evidence of inbreeding avoidance at both stages. However, results from generalized linear mixed models suggest that the pattern of MHC-dependent disassortative mating could be a by-product of inbreeding avoidance. Our results therefore suggest that while multiple apparent mechanisms of non-random mating with respect to the MHC may occur, some of them have alternative explanations.

Within-trio tests provide little support for post-copulatory selection on major histocompatibility complex haplotypes in a free-living population

Sexual selection has been proposed as a force that could help maintain the diversity of major histocompatibility complex (MHC) genes in vertebrates. Potential selective mechanisms can be divided into pre-copulatory and post-copulatory, and in both cases, the evidence for occurrence is mixed, especially in natural populations. In this study, we used a large number of parent-offspring trios that were diplotyped for MHC class II genes in a wild population of Soay sheep (Ovis aries) to examine whether there was within-trio post-copulatory selection on MHC class II genes at both the haplotype and diplotype levels. We found there was transmission ratio distortion of one of the eight MHC class II haplotypes (E) which was transmitted less than expected by fathers, and transmission ratio distortion of another haplotype (A) which was transmitted more than expected by chance to male offspring. However, in both cases, these deviations were not significant after correction for multiple tests. In addition, we did not find any evidence of post-copulatory selection at the diplotype level. These results imply that, given known parents, there is no strong post-copulatory selection on MHC class II genes in this population.

Female-Based Patterns and Social Function in Avian Chemical Communication

Much of the growing interest in avian chemical signals has focused on the role of kin recognition or mate attraction, often with an emphasis on males, with uropygial gland secretions perhaps providing information about an individual's identity and quality. Yet, data collected to date suggest sexual dimorphism in uropygial glands and secretions are often emphasized in female, rather than in male birds. That is, when a sexual difference occurs (often during the breeding season only), it is the female that typically exhibits one of three patterns: (1) a larger uropygial gland, (2) a greater abundance of volatile or semi-volatile preen oil compounds and/or (3) greater diversity of preen oil compounds or associated microbes. These patterns fit a majority of birds studied to date (23 of 30 chemically dimorphic species exhibit a female emphasis). Multiple species that do not fit are confounded by a lack of data for seasonal effects or proper quantitative measures of chemical compounds. We propose several social functions for these secretions in female-based patterns, similar to those reported in mammals, but which are largely unstudied in birds. These include: (1) intersexual advertisement of female receptivity or quality, including priming effects on male physiology, (2) intrasexual competition, including scent marking and reproductive suppression or (3) parental behaviors, such as parent-offspring recognition and chemical protection of eggs and nestlings. Revisiting the gaps of chemical studies to quantify the existence of female social chemosignals and any fitness benefit(s) during breeding are potentially fruitful but overlooked areas of future research.

Neural and molecular mechanisms underlying female mate choice decisions in vertebrates

Female mate choice is a dynamic process that allows individuals to selectively mate with those of the opposite sex that display a preferred set of traits. Because in many species males compete with each other for fertilization opportunities, female mate choice can be a powerful agent of sexual selection, often resulting in highly conspicuous traits in males. Although the evolutionary causes and consequences of the ornamentation and behaviors displayed by males to attract mates have been well studied, embarrassingly little is known about the proximate neural mechanisms through which female choice occurs. In vertebrates, female mate choice is inherently a social behavior, and although much remains to be discovered about this process, recent evidence suggests the neural substrates and circuits underlying other fundamental social behaviors (such as pair bonding, aggression and parental care) are likely similarly recruited during mate choice. Notably, female mate choice is not static, as social and ecological environments can shape the brain and, consequently, behavior in specific ways. In this Review, we discuss how social and/or ecological influences mediate female choice and how this occurs within the brain. We then discuss our current understanding of the neural substrates underlying female mate choice, with a specific focus on those that also play a role in regulating other social behaviors. Finally, we propose several promising avenues for future research by highlighting novel model systems and new methodological approaches, which together will transform our understanding of the causes and consequences of female mate choice.

Do olfactory cues from males with different avpr1a genotypes affect female mate choice in prairie voles, Microtus ochrogaster?

Multiple hypotheses have been proposed to explain female mate choice and some of the mechanisms underlying these choices. Females prairie voles display social and mating preferences for males with longer avpr1a microsatellite alleles, which provide more paternal care and exhibit less interest in novel females compared to males with shorter avpr1a microsatellite alleles. The cues females use to differentiate among males with different avpr1a genotypes are unknown, so the objective of our study was to determine if females can discriminate among males with different avpr1a genotypes using only male olfactory cues. In a laboratory choice test, females simultaneously presented with soiled bedding from a male with short versus long avpr1a microsatellite alleles showed no significant difference in the total time spent investigating each type of bedding. Nor did a greater number of females spend more time investigating soiled bedding from males with short versus long avpr1a microsatellite alleles. These findings were not influenced by female estrous status or their own avpr1a genotype. Our results suggest olfactory cues alone are insufficient to explain a female's ability to discriminate between males with different avpr1a genotypes and future research should focus on different cues or a combination of cues.

Individual Chemical Profiles in the Leach's Storm-Petrel

Avian chemical communication, once largely overlooked, is a growing field that has revealed the important role that olfaction plays in the social lives of some birds. Leach's storm-petrels (Oceanodroma leucorhoa) have a remarkable sense of smell and a strong, musky scent. This long-lived, monogamous seabird relies on olfaction for nest relocation and foraging, but whether they use scent for communication is less well studied. They are nocturnally active at the breeding colony and yet successfully reunite with their mate despite poor night-vision, indicating an important role for non-visual communication. We investigated the chemical profiles of Leach's storm-petrels to determine whether there is socially relevant information encoded in their plumage odor. To capture the compounds comprising their strong scent, we developed a method to study the compounds present in the air surrounding their feathers using headspace stir bar sorptive extraction coupled with gas chromatography-mass spectrometry. We collected feathers from Leach's storm-petrels breeding on Bon Portage Island in Nova Scotia, Canada in both 2015 and 2016. Our method detected 142 commonly occurring compounds. We found interannual differences in chemical profiles between the two sampling years. Males and females had similar chemical profiles, while individuals had distinct chemical signatures across the two years. These findings suggest that the scent of the Leach's storm-petrel provides sociochemical information that could facilitate olfactory recognition of individuals and may inform mate choice decisions.

Adult survival in migratory caribou is negatively associated with MHC functional diversity

Genes of the major histocompatibility complex (MHC) are involved in acquired immunity in vertebrates. Only a few studies have investigated the fitness consequences of MHC gene diversity in wild populations. Here, we looked at the association between annual survival and body mass and MHC-DRB exon 2 (MHC-DRB) genetic diversity, obtained from high-throughput sequencing, in two declining migratory caribou (Rangifer tarandus) herds. To disentangle the potential direct and general effects of MHC-DRB genetic diversity, we compared different indices of diversity that were either based on DNA-sequence variation or on physicochemical divergence of the translated peptides, thereby covering a gradient of allelic-to-functional diversity. We found that (1) body mass was not related to MHC-DRB diversity or genotype, and (2) adult survival probability was negatively associated with point accepted mutation distance, a corrected distance that considers the likelihood of each amino acid substitution to be accepted by natural selection. In addition, we found no evidence of fluctuating selection over time on MHC-DRB diversity. We concluded that direct effects were involved in the negative relationship between MHC functional diversity and survival, although the mechanism underlying this result remains unclear. A possible explanation could be that individuals with higher MHC diversity suffer higher costs of immunity (immunopathology). Our results suggest that genetic diversity is not always beneficial even in genes that are likely to be strongly shaped by balancing selection.

Female mate choice and species recognition between two closely related cichlid fish of Lake Malawi, Metriaclima estherae and M. callainos

Cichlids are one of the most diverse and colourful groups of freshwater fishes in the world. Despite much investigation, the factors that promote speciation in these fishes are still uncertain. However, previous studies suggest that sexual selection on male colour is one of the main drivers of speciation among these fishes. Metriaclima estherae is a polymorphic cichlid species from Lake Malawi, and thus provides an ideal model for the investigation of the importance of colour as a species recognition cue. M. callainos is a closely related and morphologically similar species, with male colour pattern very similar to that of M. estherae. We tested female choice by giving females of the two species a choice between conspecific and heterospecific males in the presence and absence of visual (colour) and chemical cues. The results show that females of M. callainos were able to reliably recognize conspecific males, even when colour was eliminated as a cue. However, females of M. estherae did not prefer conspecific males, although they were able to discriminate between red and blue conspecific colour morphs by using chemical cues. These results suggest that species recognition cues may differ even among closely related species of cichlid fish, and that female preferences for male coloration may be weak in certain species.

Mating preferences can drive expansion or contraction of major histocompatibility complex gene family

Major histocompatibility complex (MHC)-based mating rules can evolve as a way to avoid inbreeding or to increase offspring immune competence. While the role of mating preference in shaping the MHC diversity in vertebrates has been acknowledged, its impact on individual MHC diversity has not been considered. Here, we use computer simulations to investigate how simple mating rules favouring MHC-dissimilar partners affect the evolution of the number of MHC variants in individual genomes, accompanying selection for resistance to parasites. We showed that the effect of such preferences could sometimes be dramatic. If preferences are aimed at avoiding identical alleles, the equilibrium number of MHC alleles is much smaller than under random mating. However, if the mating rule minimizes the ratio of shared to different alleles in partners, MHC number is higher than under random mating. Additionally, our simulations revealed that a negative correlation between the numbers of MHC variants in mated individuals can arise from simple rules of MHC-disassortative mating. Our results reveal unexpected potential of MHC-based mating preferences to drive MHC gene family expansions or contractions and highlight the need to study the mechanistic basis of such preferences, which is currently poorly understood.

Endless forms of sexual selection

In recent years, the field of sexual selection has exploded, with advances in theoretical and empirical research complementing each other in exciting ways. This perspective piece is the product of a "stock-taking" workshop on sexual selection and sexual conflict. Our aim is to identify and deliberate on outstanding questions and to stimulate discussion rather than provide a comprehensive overview of the entire field. These questions are organized into four thematic sections we deem essential to the field. First we focus on the evolution of mate choice and mating systems. Variation in mate quality can generate both competition and choice in the opposite sex, with implications for the evolution of mating systems. Limitations on mate choice may dictate the importance of direct vs. indirect benefits in mating decisions and consequently, mating systems, especially with regard to polyandry. Second, we focus on how sender and receiver mechanisms shape signal design. Mediation of honest signal content likely depends on integration of temporally variable social and physiological costs that are challenging to measure. We view the neuroethology of sensory and cognitive receiver biases as the main key to signal form and the 'aesthetic sense' proposed by Darwin. Since a receiver bias is sufficient to both initiate and drive ornament or armament exaggeration, without a genetically correlated or even coevolving receiver, this may be the appropriate 'null model' of sexual selection. Thirdly, we focus on the genetic architecture of sexually selected traits. Despite advances in modern molecular techniques, the number and identity of genes underlying performance, display and secondary sexual traits remains largely unknown. In-depth investigations into the genetic basis of sexual dimorphism in the context of long-term field studies will reveal constraints and trajectories of sexually selected trait evolution. Finally, we focus on sexual selection and conflict as drivers of speciation. Population divergence and speciation are often influenced by an interplay between sexual and natural selection. The extent to which sexual selection promotes or counteracts population divergence may vary depending on the genetic architecture of traits as well as the covariance between mating competition and local adaptation. Additionally, post-copulatory processes, such as selection against heterospecific sperm, may influence the importance of sexual selection in speciation. We propose that efforts to resolve these four themes can catalyze conceptual progress in the field of sexual selection, and we offer potential avenues of research to advance this progress.

Experimental evidence that symbiotic bacteria produce chemical cues in a songbird

Symbiotic microbes that inhabit animal scent glands can produce volatile compounds used as chemical signals by the host animal. Though several studies have demonstrated correlations between scent gland bacterial community structure and host animal odour profiles, none have systematically demonstrated a causal relationship. In birds, volatile compounds in preen oil secreted by the uropygial gland serve as chemical cues and signals. Here, we tested whether manipulating the uropygial gland microbial community affects chemical profiles in the dark-eyed junco (Junco hyemalis). We found an effect of antibiotic treatment targeting the uropygial gland on both bacterial and volatile profiles. In a second experiment, we cultured bacteria from junco preen oil, and found that all of the cultivars produced at least one volatile compound common in junco preen oil, and that most cultivars produced multiple preen oil volatiles. In both experiments, we identified experimentally generated patterns in specific volatile compounds previously shown to predict junco reproductive success. Together, our data provide experimental support for the hypothesis that symbiotic bacteria produce behaviourally relevant volatile compounds within avian chemical cues and signals.

Evidence for odour-mediated assortative mating in humans: The impact of hormonal contraception and artificial fragrances

There is substantial evidence for assortative partner preferences in humans based on physical characteristics. In contrast, evidence suggests that olfactory preferences tend to be disassortative, with people preferring body odour of potential partners who are dissimilar at key genetic loci, perhaps to gain fitness advantage through offspring heterozygosity. We compared ratings of perceived body odour similarity of real couples with those of randomly paired 'fake' couples. Contrary to prediction, we find that odours of real partners are perceived more, rather than less, similar to each other than fake couples. However, this applied only to natural odour samples: there were no differences in similarity levels of real and fake couples' samples which were collected while wearing artificial fragrances. Furthermore, in light of suggestions that hormonal contraception (HC) disrupts disassortative odour preferences in women, we compared odour similarity among real couples in which the female partner was using or not using HC at the time when the relationship began. We find that odours of HC-using couples are of intermediate similarity between non-using and fake couples, suggesting that HC use during partner choice could affect odour-influenced assortment. We also examined the association between relationship satisfaction and perceived similarity of unfragranced odours of real couples. We found that these are positively correlated in male partners but negatively correlated in the female partners, indicative of a sex difference in the relative favourability of odour similarity in partner preference. Finally, by comparing odour similarity ratings with those given by perfumers using a novel olfactory lexicon we found evidence that similarity judgements were based on the Spicy/Animalic aspects of individual odour profiles. Taken together, our results challenge the conventional view that odour-mediated partner preferences in humans are typically disassortative.

Polymorphism of MHC class IIB in an acheilognathid species, Rhodeus sinensis shaped by historical selection and recombination

BACKGROUND

Rhodeus sinensis is a bitterling species occurring throughout the numerous freshwater systems on the East Asia. Here, we analyzed the diversity of the MHC class IIB (DAB) genes from this species, which may offer meaningful insights into evolutionary processes in this species as well as other bitterlings.

RESULTS

Using cDNA and gDNA samples from 50 individuals, we discovered classical 140 allelic sequences that could be allocated into either DAB1 (Rhsi-DAB1) or DAB3 (Rhsi-DAB3). DAB sequences completely lacking the intron, but identical or similar to Rhsi-DAB1, were also discovered from our gDNA samples, and this intron loss likely originated from the retrotransposition events of processed mDNA. The β1 domain was the most polymorphic in both Rhsi-DAB1 and -DAB3. Putative peptide biding residues (PBRs) in Rhsi-DAB1, but not in Rhsi-DAB3, exhibited a significant dN/dS, presumably indicating that different selection pressures have acted on those two DABs. Recombination between different alleles seemed to have contributed to the increase of diversity in Rhsi-DABs. Upon phylogenetic analysis, Rhsi-DAB1 and -DAB3 formed independent clusters. Several alleles from other species of Cypriniformes were embedded in the clade of Rhsi-DAB1, whereas Rhsi-DAB3 clustered with alleles from the wider range of taxa (Cyprinodontiformes), indicating that these two Rhsi-DABs have taken different historical paths.

CONCLUSIONS

A great deal of MHC class IIB allelic diversity was found in R. sinensis, and gene duplication, selection and recombination may have contributed to this diversity. Based on our data, it is presumed that such historical processes have commonly or differently acted on the polymorphism of Rhsi-DAB1 and -DAB3.

The best smellers make the best choosers: mate choice is affected by female chemosensory receptor gene diversity in a mammal

The products of the genes of the major histocompatibility complex (MHC) are known to be drivers of pathogen resistance and sexual selection enhancing offspring genetic diversity. The MHC further influences individual odour types and social communication. However, little is known about the receptors and their volatile ligands that are involved in this type of chemical communication. Here, we have investigated chemosensory receptor genes that ultimately enable females to assess male genes through odour cues. As a model, we used an invasive population of North American raccoons ( Procyon lotor) in Germany. We investigated the effect of two groups of chemosensory receptor genes-trace amine-associated receptors (TAARs) and olfactory receptors (ORs)-on MHC-dependent mate choice. Females with more alleles of the TAAR or OR loci were more likely to choose a male with a diverse MHC. We additionally found that MHC class I genes have a stronger effect on mate choice than the recently reported effect for MHC class II genes, probably because of their immunological relevance for viral resistance. Our study is among the first to show a genetic link between behaviour and chemosensory receptor genes. These results contribute to understanding the link between genetics, olfaction and associated life-history decisions.

Genetic variation at MHC class II loci influences both olfactory signals and scent discrimination in ring-tailed lemurs

BACKGROUND

Diversity at the Major Histocompatibility Complex (MHC) is critical to health and fitness, such that MHC genotype may predict an individual's quality or compatibility as a competitor, ally, or mate. Moreover, because MHC products can influence the components of bodily secretions, an individual's body odors may signal its MHC composition and influence partner identification or mate choice. Here, we investigated MHC-based signaling and recipient sensitivity by testing for odor-gene covariance and behavioral discrimination of MHC diversity and pairwise dissimilarity in a strepsirrhine primate, the ring-tailed lemur (Lemur catta).

METHODS

First, we coupled genotyping of the MHC class II gene, DRB, with gas chromatography-mass spectrometry of genital gland secretions to investigate if functional genetic diversity is signaled by the chemical diversity of lemur scent secretions. We also assessed if the chemical similarity between individuals correlated with their MHC-DRB similarity. Next, we assessed if lemurs discriminated this chemically encoded, genetic information in opposite-sex conspecifics.

RESULTS

We found that both sexes signaled overall MHC-DRB diversity and pairwise MHC-DRB similarity via genital secretions, but in a sex- and season-dependent manner. Additionally, the sexes discriminated absolute and relative MHC-DRB diversity in the genital odors of opposite-sex conspecifics, suggesting that lemur genital odors function to advertise genetic quality.

CONCLUSIONS

In summary, genital odors of ring-tailed lemurs provide honest information about an individual's absolute and relative MHC quality. Complementing evidence in humans and Old World monkeys, we suggest that reliance on scent signals to communicate MHC quality may be important across the primate lineage.

MHC class I diversity predicts non-random mating in Chinese alligators (Alligator sinensis)

The major histocompatibility complex (MHC) has several important roles in kin recognition, pathogen resistance and mate selection. Research in fish, birds and mammals has suggested that individuals optimise MHC diversity, and therefore offspring fitness, when choosing mates. In reptiles, however, it is unclear whether female mate choice is based on genome-wide genetic characteristics such as microsatellite DNA loci, particular functional-trait loci (e.g., MHC) or both, and MHC's effects on mate choice remain relatively understudied. Herein, we used 13 microsatellite loci and two MHC class I loci to investigate female mate choice of Chinese alligators (Alligator sinensis) in the semi-natural condition. We also determined correlations between the MHC genotype of breeding males and male reproductive success. We found that MHC-heterozygous males harbour a greater reproductive success, which probably is the reason that these males are more preferred by the females than MHC-homozygous males. Furthermore, the MHC class I amino-acid distance and functional distance of true mating pairs were higher compared with those of randomly sampled pairs. Analysis of microsatellites revealed that, despite mate choice, females did not completely avoid inbreeding. These findings are the first evidence of MHC-associated mate choice in Chinese alligators, suggesting that females may adopt different mating strategies after assessing the MHC characteristics of potential mates.

Possible reproductive benefits to female Carpetan rock lizards of pre-sensory bias towards chemical signals

Female Carpetan rock lizards (Iberolacerta cyreni) might assess the quality of males from their chemical signals. Females select areas scent marked by males with secretions containing high proportions of provitamin D to ensure mating with high-quality males. However, an alternative explanation might be that females are not choosing a mate, but that females have a pre-sensory bias for chemical cues of vitamin D in the food and are, in fact, assessing habitat quality to obtain direct benefits of increasing the intake of vitamin D. We evaluated experimentally the possible benefits of a nutritional supplement of provitamin D or vitamin D in pregnant females for their clutches and offspring. However, we did not find large differences between treatments, except in the lower body condition of juveniles of mothers supplemented with provitamin D. We also tested the chemosensory interest of females in the scent of males to study the existence of a sensory bias; this response decreased when the amount of dietary vitamin D exceeded their needs. The results suggest that there are no reproductive benefits in the intake of additional vitamin D and that the potential sensory bias to scents of males could be related to the physiological needs of the females.

Utilizing herbarium specimens to quantify historical mycorrhizal communities

PREMISE OF THE STUDY

Mycorrhiza are critical to ecosystem functioning, but a lack of historical baseline data limits our understanding of the long-term belowground effects of global change. Herbarium specimens may provide this needed insight. However, it is unknown whether DNA of arbuscular mycorrhizal fungi (AMF) can be reliably extracted from vascular plant specimen roots.

METHODS

We sampled roots from herbarium specimens of four herbaceous forest species collected in western Pennsylvania between 1881-2008. Using molecular methods (terminal restriction fragment length polymorphism and sequence analysis), we quantified AMF communities from specimen roots and tested for contamination.

RESULTS

We successfully amplified AMF DNA from 44% (21/48) of the root but not leaf samples, indicating specimen contamination was negligible. As expected, there were significant differences in AMF composition between plant species (P < 0.05). However, no differences in AMF communities were detected through time, possibly due to limited sample size and low amplification rates in recent collections.

DISCUSSION

Herbaria have potential as sources of valuable belowground microbial data to answer questions across geographic, temporal, and taxonomic scales otherwise not feasible. Ongoing methodological developments will only magnify this potential. Further tests are needed to determine curatorial practices that maximize this innovative use of herbarium specimens.

Behavioural and neuronal basis of olfactory imprinting and kin recognition in larval fish

Imprinting is a specific form of long-term memory of a cue acquired during a sensitive phase of development. To ensure that organisms memorize the right cue, the learning process must happen during a specific short time period, mostly soon after hatching, which should end before irrelevant or misleading signals are encountered. A well-known case of olfactory imprinting in the aquatic environment is that of the anadromous Atlantic and Pacific salmon, which prefer the olfactory cues of natal rivers to which they return after migrating several years in the open ocean. Recent research has shown that olfactory imprinting and olfactory guided navigation in the marine realm are far more common than previously assumed. Here, we present evidence for the involvement of olfactory imprinting in the navigation behaviour of coral reef fish, which prefer their home reef odour over that of other reefs. Two main olfactory imprinting processes can be differentiated: (1) imprinting on environmental cues and (2) imprinting on chemical compounds released by kin, which is based on genetic relatedness among conspecifics. While the first process allows for plasticity, so that organisms can imprint on a variety of chemical signals, the latter seems to be restricted to specific genetically determined kin signals. We focus on the second, elucidating the behavioural and neuronal basis of the imprinting process on kin cues using larval zebrafish (Danio rerio) as a model. Our data suggest that the process of imprinting is not confined to the central nervous system but also triggers some changes in the olfactory epithelium.

Plumage microbiota covaries with the major histocompatibility complex in blue petrels

To increase fitness, a wide range of vertebrates preferentially mate with partners that are dissimilar at the major histocompatibility complex (MHC) or that have high MHC diversity. Although MHC often can be assessed through olfactory cues, the mechanism by which MHC genes influence odour remains largely unclear. MHC class IIB molecules, which enable recognition and elimination of extracellular bacteria, have been suggested to influence odour indirectly by shaping odour-producing microbiota, i.e. bacterial communities. However, there is little evidence of the predicted covariation between an animal's MHC genotype and its bacterial communities in scent-producing body surfaces. Here, using high-throughput sequencing, we tested the covariation between MHC class IIB genotypes and feather microbiota in the blue petrel (Halobaena caerulea), a seabird with highly developed olfaction that has been suggested to rely on oduor cues during an MHC-based mate choice. First, we show that individuals with similar MHC class IIB profiles also have similar bacterial assemblages in their feathers. Then, we show that individuals with high MHC diversity have less diverse feather microbiota and also a reduced abundance of a bacterium of the genus Arsenophonus, a genus in which some species are symbionts of avian ectoparasites. Our results, showing that feather microbiota covary with MHC, are consistent with the hypothesis that individual MHC genotype may shape the semiochemical-producing microbiota in birds.

Human Leukocyte Antigen similarity decreases partners' and strangers' body odor attractiveness for women not using hormonal contraception

The Human Leukocyte Antigen (HLA) is a gene complex that encodes important elements of the human immune system. HLA profile is communicated via olfaction and interindividual diversity is assumed to be advantageous for mate choice. Additionally, HLA diversity appears to enhance satisfaction and sexual attraction in existing romantic partnerships. However, whether this effect is transmitted via body odors and whether it results in an attraction towards HLA-dissimilar individuals and/or an avoidance of HLA-similar ones remains unclear. In the present study, we genotyped couples and asked each participant to rate a body odor sample from their partner and from three strangers of the opposite sex who expressed a similar or dissimilar HLA-B and HLA-C genotype. We found no statistically significant preference for HLA similarity or dissimilarity in men. Among women, the observed effects differed depending on hormonal contraception status. Like men, women on hormonal contraception did not exhibit significant HLA-related preferences. However, for women not using hormonal contraceptives, odors from HLA-B and HLA-C similar donors were significantly less attractive than those from HLA-dissimilar donors, regardless of whether the samples were from a partner or a stranger. Our findings support the hypothesis that HLA similarity is perceived via body odors and that such similarity affects human attraction. This mechanism may serve an evolutionarily adaptive function in preventing prospective offspring from having decreased immunocompetence, or decreasing the chance of kin mating.

Sperm is a sexual ornament in rose bitterling

In many taxa, odour cues mediate mating decisions. A key question is what these odours comprise, where they are produced, and what they signal. Using rose bitterling, fish that spawn in the gills of freshwater mussels, we investigated the role of sperm cues on female oviposition decisions using individuals of known MHC genotype. Male bitterling frequently released sperm prior to female oviposition and females responded with an increased probability of oviposition and released a greater number of eggs, particularly if males had a dissimilar MHC genotype. These mating preferences by females were shown to be adaptive, with MHC dissimilarity of males and females correlated positively with embryo survival. These results support a role for indirect benefits to rose bitterling mate choice, and we propose that sperm acts as a releaser pheromone in bitterling, functioning as a sexual ornament signalling male quality as a mate.

Ecology can inform genetics: Disassortative mating contributes to MHC polymorphism in Leach's storm-petrels (Oceanodroma leucorhoa)

Studies of MHC-based mate choice in wild populations often test hypotheses on species exhibiting female choice and male-male competition, which reflects the general prevalence of females as the choosy sex in natural systems. Here, we examined mutual mate-choice patterns in a small burrow-nesting seabird, the Leach's storm-petrel (Oceanodroma leucorhoa), using the major histocompatibility complex (MHC). The life history and ecology of this species are extreme: both partners work together to fledge a single chick during the breeding season, a task that requires regularly travelling hundreds of kilometres to and from foraging grounds over a 6- to 8-week provisioning period. Using a 5-year data set unprecedented for this species (n = 1078 adults and 925 chicks), we found a positive relationship between variation in the likelihood of female reproductive success and heterozygosity at Ocle-DAB2, a MHC class IIB locus. Contrary to previous reports rejecting disassortative mating as a mechanism for maintaining genetic polymorphism in this species, here we show that males make significant disassortative mate-choice decisions. Variability in female reproductive success suggests that the most common homozygous females (Ocle-DAB2*01/Ocle-DAB2*01) may be physiologically disadvantaged and, therefore, less preferred as lifelong partners for choosy males. The results from this study support the role of mate choice in maintaining high levels of MHC variability in a wild seabird species and highlight the need to incorporate a broader ecological framework and sufficient sample sizes into studies of MHC-based mating patterns in wild populations in general.

Characterization of Chemical Constituents of Human Sweat: A Study Based on Indian Population

There is a strong evidence in the literature that human odor is unique to an individual; therefore, the focus of this study was to strengthen this evidence through the testing of sweat samples on unrelated individuals with the same ethnicity. Sweat samples were collected from 42 unrelated Indian males and females residing in the same city to determine the chemical constituents in human sweat. The volatile compounds of sweat were subsequently analyzed and identified using gas chromatography-mass spectrometry, and a National Institute of Standards and Technology library was used for individual profiling. A total of 78 compounds were identified in human sweat tested with 22 compounds found to be unique to the individual (frequency of occurrence one). A scent profile, or "chexmotype," unique to the sweat of each individual was obtained. This is the first extensive study on an Indian population with 36 new compounds detected in human sweat.

MHC-mediated sexual selection on birdsong: Generic polymorphism, particular alleles and acoustic signals

Several hypotheses predict that the major histocompatibility complex (MHC) drives mating preference in females. Olfactory, colour or morphological traits are often found as reliable signals of the MHC profile, but the role of avian song mediating MHC-based female choice remains largely unexplored. We investigated the relationship between several MHC and acoustic features in the collared flycatcher (Ficedula albicollis), a European passerine with complex songs. We screened a fragment of the class IIB second exon of the MHC molecule, of which individuals harbour 4-15 alleles, while considerable sequence diversity is maintained at the population level. To make statistical inferences from a large number of comparisons, we adopted both null-hypothesis testing and effect size framework in combination with randomization procedures. After controlling for potential confounding factors, neither MHC allelic diversity nor the presence of particular alleles was associated remarkably with the investigated qualitative and quantitative song traits. Furthermore, genetic similarity among males based on MHC sequences was not reflected by the similarity in their song based on syllable content. Overall, these results suggest that the relationship between features of song and the allelic composition and diversity of MHC is not strong in the studied species. However, a biologically motivated analysis revealed that individuals that harbour an MHC allele that impairs survival perform songs with broader frequency range. This finding suggests that certain aspects of the song may bear reliable information concerning the MHC profile of the individuals, which can be used by females to optimize mate choice.

Why do some animals mate with one partner rather than many? A review of causes and consequences of monogamy

Why do some animals mate with one partner rather than many? Here, I investigate factors related to (i) spatial constraints (habitat limitation, mate availability), (ii) time constraints (breeding synchrony, length of breeding season), (iii) need for parental care, and (iv) genetic compatibility, to see what support can be found in different taxa regarding the importance of these factors in explaining the occurrence of monogamy, whether shown by one sex (monogyny or monandry) or by both sexes (mutual monogamy). Focusing on reproductive rather than social monogamy whenever possible, I review the empirical literature for birds, mammals and fishes, with occasional examples from other taxa. Each of these factors can explain mating patterns in some taxa, but not in all. In general, there is mixed support for how well the factors listed above predict monogamy. The factor that shows greatest support across taxa is habitat limitation. By contrast, while a need for parental care might explain monogamy in freshwater fishes and birds, there is clear evidence that this is not the case in marine fishes and mammals. Hence, reproductive monogamy does not appear to have a single overriding explanation, but is more taxon specific. Genetic compatibility is a promising avenue for future work likely to improve our understanding of monogamy and other mating patterns. I also discuss eight important consequences of reproductive monogamy: (i) parentage, (ii) parental care, (iii) eusociality and altruism, (iv) infanticide, (v) effective population size, (vi) mate choice before mating, (vii) sexual selection, and (viii) sexual conflict. Of these, eusociality and infanticide have been subject to debate, briefly summarised herein. A common expectation is that monogamy leads to little sexual conflict and no or little sexual selection. However, as reviewed here, sexual selection can be substantial under mutual monogamy, and both sexes can be subject to such selection. Under long-term mutual monogamy, mate quality is obviously more important than mate numbers, which in turn affects the need for pre-mating mate choice. Overall, I conclude that, despite much research on genetic mating patterns, reproductive monogamy is still surprisingly poorly understood and further experimental and comparative work is needed. This review identifies several areas in need of more data and also proposes new hypotheses to test.

Selection outweighs drift at a fine scale: Lack of MHC differentiation within a family living lizard across geographically close but disconnected rocky outcrops

The highly polymorphic genes of the major histocompatibility complex (MHC) are involved in disease resistance, mate choice and kin recognition. Therefore, they are widely used markers for investigating adaptive variation. Although selection is the key driver, gene flow and genetic drift also influence adaptive genetic variation, sometimes in opposing ways and with consequences for adaptive potential. To further understand the processes that generate MHC variation, it is helpful to compare variation at the MHC with that at neutral genetic loci. Differences in MHC and neutral genetic variation are useful for inferring the relative influence of selection, gene flow and drift on MHC variation. To date, such investigations have usually been undertaken at a broad spatial scale. Yet, evolutionary and ecological processes can occur at a fine spatial scale, particularly in small or fragmented populations. We investigated spatial patterns of MHC variation among three geographically close, naturally discrete, sampling sites of Egernia stokesii, an Australian lizard. The MHC of E. stokesii has recently been characterized, and there is evidence for historical selection on the MHC. We found E. stokesii MHC weakly differentiated among sites compared to microsatellites, suggesting selection, acting similarly at each site, has outweighed any effects of low gene flow or of genetic drift on E. stokesii MHC variation. Our findings demonstrate the strength of selection in shaping patterns of MHC variation or consistency at a fine spatial scale.

Impact of male presence on female sociality and stress endocrinology in wild house mice (Mus musculus domesticus)

In group living animals, reproductive competition plays an important role in shaping social relationships and associations among female group members. In this study, we investigated the impact of male presence on the development of female-female competition and female sociality in groups of female wild house mice, using physiological and behavioral parameters. We predicted that, by eliciting intra-sexual competition, males influence social relationships among female group members and thus affect female associations to potential cooperation partners. To test this hypothesis we compared stress hormone production, the frequency of agonistic interactions, social hierarchies and social partner preferences in groups of unrelated, unfamiliar females in the absence and presence of males. Our results revealed no indication that the introduction of males into all-female groups of wild house mice elicited increased competition among female group members, neither on the physiological nor on the behavioral level. We found no effect of male presence on female glucocorticoid secretion, aggression, dominance hierarchies or on the females' sociability. Females thus seem not to intensely compete over access to males. This female ability to behaviorally and physiologically deal with even previously unfamiliar same-sex group members may be an important feature of female house mouse societies. In fact, it could be a necessary prerequisite to establish cooperative relationships between females in the context of reproduction, such as communal nursing of young.