Arranged and non-arranged marriages have similar reproductive outcomes in Nepal

Much of the evolutionary literature on mate choice presumes that individual mate preferences function to increase individual fitness, and this assumption has been confirmed in several experimental studies with animals. However, human mate choice, in many cultures, is heavily controlled by parents via arranged marriages, rather than the selection of the marrying individuals. Several studies have demonstrated that parents and offspring do not exhibit identical preferences for an in-law or spouse, respectively. If parental choice thwarts offspring's evolved mate preferences from being expressed, then arranged marriages should reduce fitness. Using data from the Chitwan Valley Family Study, I examined whether having an arranged marriage, as compared to a non-arranged marriage, is associated with differences in total births, offspring survival to age 15, or interbirth intervals in Nepal, a culture with a rich history of arranged marriage. I find that there are no differences in any reproductive outcomes between arranged, co-selected, and self-selected marriages. These results indicate that individuals in arranged and non-arranged marriages may achieve similar fitness outcomes via different pathways, which may be unique to human mating systems.

Social opportunities and mate preference improve breeding success in Caribbean iguanas

Conservation breeding of West Indian rock iguanas (Cyclura) has met with limited success historically. Many facilities witness high levels of aggression and mate incompatibility resulting in failed breeding introductions which often require animals to be separated. This may be due, in part, to lack of knowledge of how mate familiarity and preference affect reproductive outcomes in these species. We investigated whether social exposure during the pre-breeding season influenced copulation success, egg production, and breeding behaviors. Additionally, we examined whether mate preference, as determined by pre-mating dichotomous choice tests, increased these reproductive outcomes. Female rock iguanas that were socialized with males prior to breeding opportunities copulated with familiar males for longer periods of time than females that were not socialized. Socialization opportunities did not alter male reproductive success measurements or breeding behavior. Female rock iguanas introduced for mating to their preferred partners had a higher probability of successful copulations, higher average number of copulations, and less resting behavior during introductions than females mated to non-preferred males. Male mate preference had no effect on reproductive success measurements during mating introductions. These results indicate that socializing animals and providing mate choice opportunities increase breeding success of rock iguanas under managed care.

Variation in mouse chemical signals is genetically controlled and environmentally modulated

In most mammals and particularly in mice, chemical communication relies on the detection of ethologically relevant fitness-related cues from other individuals. In mice, urine is the primary source of these signals, so we employed proteomics and metabolomics to identify key components of chemical signalling. We show that there is a correspondence between urinary volatiles and proteins in the representation of genetic background, sex and environment in two house mouse subspecies Mus musculus musculus and M. m. domesticus. We found that environment has a strong influence upon proteomic and metabolomic variation and that volatile mixtures better represent males while females have surprisingly more sex-biased proteins. Using machine learning and combined-omics techniques, we identified mixtures of metabolites and proteins that are associated with biological features.

Cognition and Its Shaping Effect on Sexual Conflict: Integrating Biology and Psychology

While genetic variation is of crucial importance for organisms to be able to adapt to their ever-changing environments over generations, cognitive processes can serve the same purpose by acting at shorter time scales. Cognition, and its resulting behaviour, allows animals to display flexible, fast and reversible responses that, without implying a genetic change, are crucial for adaptation and survival. In the research field on sexual conflict, where studies focus on male and female mating strategies that increase the individual’s reproductive fitness while forcing a cost on the partner, the role that cognition may play in how such strategies can be optimised has been widely overlooked. However, a careful analysis of behavioural studies shows that animals can develop and change their responses depending on what they perceive as well as on what they can predict from their experience, which can be of prime importance for optimising their reproductive fitness. As will be reviewed here, largely psychological processes, such as perception, memory, learning and decision-making, can not only modulate sexual conflict, but can also have a big impact on the reproductive success of a given individual. This review highlights the need for a more integrative view of sexual conflict where cognitive processes are also considered as a fundamental part of an animal’s adaptive mating response.

Experimental evidence that adult UV/yellow colouration functions as a signal in blue tit families — but only for parents

Abstract

In bi-parental species, reproduction is not only a crucial life-history stage where individuals must take fitness-related decisions, but these decisions also need to be adjusted to the behavioural strategies of other individuals. Hence, communication is required, which could be facilitated by informative signals. Yet, these signalling traits might have (co-)evolved in multiple contexts, as various family members usually meet and interact during reproduction. In this study, we experimentally explored for the first time whether a colourful plumage trait in adults acts as a signal that regulates multiple intra-family interactions in a bird species, the blue tit (Cyanistes caeruleus). We expected that an experimental reduction of adults’ UV/yellow reflectance (i.e. a reduction of apparent individual quality) should affect the behavioural strategies of all family members. We found evidence for this at least in adults, since the partners of UV-blocked individuals (either males or females) increased their parental investment — perhaps to compensate for the apparent lower condition of their mates. As the UV-blocked adult did not change its provisioning behaviour, the partner presumably responded to the manipulated signal and not to a behavioural change. However, the offspring did not co-adjust their begging intensity to the experimental treatment. It is thus possible that they responded to overall parental care rather than the signal. These results suggest that UV/yellow colouration of adult blue tits may act as quality signal revealing the rearing capacity to mates.

Significance statement

How parents respond to signals of genetic or phenotypic quality of their mates has received significant attention. However, previous studies have primarily focused on the receiver’s response and have not always controlled for the signaller’s behaviour and its investment in reproduction. Our results provide the first experimental evidence that ultraviolet (UV)/yellow colouration acts as a signal of parental quality in the blue tit. Parents responded by increasing their effort when paired with UV-blocked (low-quality) mates, while controlling for the mate’s behaviour. We argue that the reduced expression of the signal triggered a compensatory response in the mate. Interestingly, both males and females responded similarly to changes in mate’s UV/yellow reflectance, suggesting similar rules over investment in response to this trait. However, nestlings, a potential (and often neglected) set of observers of parental signals, did not change their behaviour when raised by an UV-blocked (= low-quality) parent.

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.

Differences in Mate Pairings of Hatchery- and Natural-Origin Coho Salmon Inferred from Offspring Genotypes

Captive breeding can affect how sexual selection acts on subsequent generations. One context where this is important is in fish hatcheries. In many salmon hatcheries, spawning is controlled artificially and offspring are reared in captivity before release into the wild. While previous studies have suggested that hatchery- and natural-origin fish may make different mate choice decisions, it remains to be determined how hatchery fish may be making different mate choice decisions compared with natural-origin fish at a genetic level. Using genotyping-by-sequencing, we identify single-nucleotide polymorphisms (SNPs) associated with variation in mate pairings from a natural context involving hatchery- and natural-origin coho salmon (Oncorhynchus kisutch). In both natural-origin and hatchery mate pairs, we observed more SNPs with negative assortment than positive assortment. However, only 3% of the negative assortment SNPs were shared between the two mating groups, and 1% of the positive assortment SNPs were shared between the two mating groups, indicating divergence in mating cues between wild and hatchery-raised salmon. These findings shed light on mate choice in general and may have important implications in the conservation management of species as well as for improving other captive breeding scenarios. There remains much to discover about mate choice in salmon and research described here reflects our intent to test the potential of ongoing advances in population genomics to develop new hatchery practices that may improve the performance of hatchery offspring, lessening the differences and thus potential impacts upon wild stocks.

Environmental influences on for-mediated oviposition decisions in Drosophila melanogaster

Deciding whether or not to lay an egg on a given substrate is an important task undertaken by females of many arthropods. It involves perceiving the environment (e.g. quality of the substrate, temperature, and humidity), formulating a decision, and then conducting the appropriate behaviours to oviposit. This oviposition site selection (OSS) provides a useful system for studying simple decision-making. OSS in fruit flies, Drosophila melanogaster, is influenced by both genetic and environmental variation. Naturally occurring allelic variation in the foraging gene (for) is known to affect OSS. Given a choice of high- and low-nutrient oviposition substrates, groups of rovers (for^R) are known to lay significantly more of their eggs on low-nutrient sites than sitters (for^s) and sitter mutants (for^s2). Here we ask three questions: (1) Is the role of for in OSS affected by the availability of alternate oviposition sites? (2) Is the role of for in OSS sensitive to the density of ovipositing females? and (3) Does the gustatory sensation of yeast play a role in for-mediated variation in OSS? We find a role of choice and female density in rover/sitter differences in OSS, as well as a role of for in response to glycerol, an indicator of yeast. The role of for in OSS decision-making is complex and multi-faceted and should prove fertile ground for further research into the factors affecting decision-making behaviours.

Temperament and sexual behaviour in the Furrowed Wood Turtle Rhinoclemmys areolata

The variation in temperament among animals has consequences for evolution and ecology. One of the primary effects of consistent behavioral differences is on reproduction. In chelonians some authors have focused on the study of temperament using different methods. In our research our first aim was i) establish a methodology to determine the degree of boldness among individuals Rhinoclemmys areolata. Our second aim was to ii) determine the role boldness plays during reproduction, with emphasis on courtship and copulation, considering a) the interactions between males and females, and b) competition between males. We used 16 sexually mature individuals of each sex. Males were observed in four different situations and 17 behavioral traits were recorded. We selected 12 traits that allowed us distinguish between the bolder and the shier individuals and found that five behavioral traits were specific for bolder individuals and five others for shier individuals. In a second step, we observed a male in presence of a female and recorded courtship behaviors and breeding attempts. Bolder individuals did not display courtship behaviors and just attempted to copulate. Shier individuals displayed courtship behaviors and copulation attempts were rarely observed. Finally, in the simulations that compared two males in the presence of a female we noticed that bolder individuals displayed courtship behaviors while the shier ones simply ignored the female. Our results first allowed us to determine which methodology is the best to determine temperament in turtles. Secondly, temperament seems to be an important factor in modulating interaction between males and females. Bolder individuals have an advantage during competition and display courtship behaviours only if other males are present. Shier males displayed courtship behaviors and only try to copulate when no competitors were present. These two different temperament-dependant strategies are discussed in terms of ecology, evolution and management.

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.

Fitness costs of mating with preferred females in a scramble mating system

Little is known about the operation of male mate choice in systems with perceived high costs to male choosiness. Scramble mating systems are one type of system in which male choice is often considered too costly to be selected. However, in many scramble mating systems, there are also potentially high rewards of male choosiness, as females vary dramatically in reproductive output and males typically mate once per season and/or per lifetime. Using scramble mating wood frogs (Rana sylvatica), we tested whether males gain fitness benefits by mating with preferred females. We conducted choice trials (1 male presented simultaneously with 2 females) and permitted males to mate with their preferred or nonpreferred female. Offspring of preferred and nonpreferred females were reared in the laboratory and field, and we quantified various fitness-relevant parameters, including survivorship and growth rates. Across multiple parameters measured, matings with preferred females produced fewer and lower-quality offspring than did those with nonpreferred females. Our results are inconsistent with the idea that mate choice confers benefits on the choosing sex. We instead propose that, in scramble systems, males will be more likely to amplex females that are easier to capture, which may correlate with lower quality but increases male likelihood of successfully mating. Such male choice may not favor increased fitness when the operational sex ratio is less biased toward males in scramble mating systems but is, instead, a bet-hedging tactic benefitting males when available females are limited.

Improving the sustainability of ex situ populations with mate choice

Many breeding programs managed by the Association of Zoos and Aquariums' (AZA) Species Survival Plans® (SSPs) are not meeting goals for population size and genetic diversity due to failure of recommended pairs to breed successfully. According to AZA Population Management Center analyses, as many as 80% of recommended breeding pairs fail to produce young before the next breeding and transfer plan is issued. Determining reasons for failure and ensuring that a specific pairing produces offspring can be challenging. Mate incompatibility, one possible reason for failure, might be addressed by allowing mate choice. Although many SSP® coordinators and breeding managers, who implement breeding recommendations at their institutions, recognize the potential benefits of mate choice, examples and models for presenting and assessing choice are lacking. Here we review examples from birds, rodents, lagomorphs, marsupials, carnivores, fishes, and insects where mate choice has been incorporated. These examples provide strong evidence that free mate choice and mating with preferred partners increase a variety of reproductive success measurements when compared to assigned mate pairings. We suggest innovative housing and breeding arrangements for better incorporating mate choice into the management strategies for species held ex situ. Further, we discuss the fitness consequences and welfare implications of allowing choice. We advocate for a more systematic use of behavioral research in cooperative breeding programs. Behavioral management for mating can yield more successful programs, thus ensuring SSP® genetic and demographic goals are met, while simultaneously improving welfare.

Sexual selection on the multicomponent display of black morph male Girardinus metallicus (Pisces: Poeciliidae)

Sexually selected displays often include suites of integrated traits. Black morph males of the poeciliid fish Girardinus metallicus perform courtship and aggressive displays that exhibit their conspicuous yellow and black coloration. Body size, gonopodium size and ventral black area are correlated with intermale aggression, which is key for access to mates. A previous study showed that females may prefer dominant males prior to watching them fight; however, that result was obtained in trials that allowed for male-male interactions across partitions, and to date no study has uncovered the traits important in female choice. We performed a more comprehensive investigation of the multicomponent sexual display including measures of male yellow hue, saturation and brightness. We examined the behavior of size-matched males paired to maximize the difference in yellow saturation, and measured female choice exclusive of male-male interactions and chemical cues. We found no female preference for any traits in the multicomponent sexual display. Males with brighter and more saturated yellow coloration were more likely to be dominant, and dominant males courted and attempted copulations more. Our results suggest that yellow coloration is sexually selected; however, the courtship display requires further investigation because we did not identify targets of female preference, and we discuss possible explanations for this finding.

Mate choice, sexual selection, and endocrine-disrupting chemicals

Humans have disproportionately affected the habitat and survival of species through environmental contamination. Important among these anthropogenic influences is the proliferation of organic chemicals, some of which perturb hormone systems, the latter referred to as endocrine-disrupting chemicals (EDCs). EDCs are widespread in the environment and affect all levels of reproduction, including development of reproductive organs, hormone release and regulation through the life cycle, the development of secondary sexual characteristics, and the maturation and maintenance of adult physiology and behavior. However, what is not well-known is how the confluence of EDC actions on the manifestation of morphological and behavioral sexual traits influences mate choice, a process that requires the reciprocal evaluation of and/or acceptance of a sexual partner. Moreover, the outcomes of EDC-induced perturbations are likely to influence sexual selection; yet this has rarely been directly tested. Here, we provide background on the development and manifestation of sexual traits, reproductive competence, and the neurobiology of sexual behavior, and evidence for their perturbation by EDCs. Selection acts on individuals, with the consequences manifest in populations, and we discuss the implications for EDC contamination of these processes, and the future of species.

Sex roles and adult sex ratios: insights from mammalian biology and consequences for primate behaviour

Theoretical models and empirical studies in various taxa have identified important links between variation in sex roles and the number of adult males and females (adult sex ratio (ASR)) in a population. In this review, I examine these relationships in non-human primates. Because most existing theoretical models of the evolution of sex roles focus on the evolutionary origins of sex-biased behaviour, they offer only a general scaffold for predicting variation in sex roles among and within species. I argue that studies examining sex role variation at these more specific levels need to take social organization into account to identify meaningful levels for the measurement of ASR and to account for the fact that ASR and sex roles mutually influence each other. Moreover, taxon-specific life-history traits can constrain sex role flexibility and impact the operational sex ratio (OSR) by specifying the minimum length of female time outs from reproduction. Using examples from the primate literature, I highlight practical problems in estimating ASR and OSR. I then argue that interspecific variation in the occurrence of indirect forms of paternal care might indeed be linked to variation in ASR. Some studies also indicate that female aggression and bonding, as well as components of inter-sexual relationships, are sensitive to variation in ASR. Thus, links between primate sex roles and sex ratios merit further study, and such studies could prompt the development of more specific theoretical models that make realistic assumptions about taxon-specific life history and social organization.This article is part of the themed issue 'Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies'.

Free mate choice does not influence reproductive success in humans

The effect of free mate choice on the relative magnitude of fitness benefits has been examined among various species. The majority of the data show significant fitness benefits of mating with partners of an individual’s own choice, highlighting elevated behavioral compatibility between partners with free mate choice. Similarities between humans and other species that benefit from free mate choice led us to hypothesize that it also confers reproductive benefits in Homo sapiens. To test this hypothesis, we conducted a study among three indigenous societies—the Tsimane’, Yali, and Bhotiya—who employ natural birth control. In all three samples, we compared the marriages arranged by parents with the non-arranged ones in terms of number of offspring. Here, we show that there were no significant relationships between type of marriage and the total number of alive children and number of dead children among the three sampled groups. The presented study is the first to date to examine the fitness benefits of free mate choice in humans. In discussion we present limitations of our research and discuss the possibility of love having a beneficial influence in terms of the number of offspring.

The molecular basis and reproductive function(s) of copulatory plugs

In many animals, male ejaculates coagulate to form what has been termed a copulatory plug, a structure that varies in size and shape but often fills and seals the female's reproductive tract. The first published observation of a copulatory plug in a mammal was made more than 160 years ago, and questions about its formation and role in reproduction continue to endear evolutionary and population geneticists, behavioral ecologists, and molecular, reproductive, and developmental biologists alike. Here, we review the current knowledge of copulatory plugs, focusing on rodents and asking two main questions: how is it formed and what does it do? An evolutionary biology perspective helps us understand the latter, potentially leading to insights into the selective regimes that have shaped the diversity of this structure. Mol. Reprod. Dev. 83: 755-767, 2016 © 2016 Wiley Periodicals, Inc.

Copulatory plugs inhibit the reproductive success of rival males

Ejaculated proteins play important roles in reproductive fitness. In many species, seminal fluid coagulates and forms what has been referred to as a copulatory plug in the female's reproductive tract. In mice, previous work demonstrated that knockout males missing a key seminal fluid protein were unable to form a plug and less successful at siring litters in noncompetitive matings (one female, one male), probably the result of reduced sperm transport or insufficient stimulation of the female. Here, we extend these previous studies to competitive matings (one female, two males) and make two key insights. First, when first males were unable to form a plug, they lost almost all paternity to second males to mate. Thus, the copulatory plugs of second males could not rescue the reduced fertility of first males. Second, we showed that the copulatory plug of first males effectively blocked fertilization by second males, even if first males were vasectomized. Taken together, our experiments demonstrated that first males lost almost all paternity if they never formed a plug. We discuss our results in the context of natural populations, where in spite of the strong effects seen here, pregnant female mice regularly carry litters fertilized by more than one male.

Rethinking Bateman's Principles: Challenging Persistent Myths of Sexually Reluctant Females and Promiscuous Males

In 1948, Angus Bateman published a paper on fruit flies that tested Charles Darwin's ideas of sexual selection. Based on this one fruit fly study, Bateman concluded that because males are able to produce millions of small sperm, males are likely to behave promiscuously, mating with as many females as possible. On the other hand, because females produce relatively fewer, larger, and presumably more expensive eggs, females are likely to be very discriminating in selecting only one high-quality sexual partner. He also posited that a male's reproductive success increases linearly with the number of females he is able to mate with, but that a female's reproductive success peaks after she mates with only one male. Consequently, in almost all organisms, sexual selection acts most strongly on males. These ideas became a recurring theme in attempts to explain wide-ranging differences in male and female behavior not only in nonhuman animals but also in humans. As such, Bateman's conclusions and predictions have become axiomatic and, at times, have gone unquestioned even when modern empirical data do not conform to this model. This article reviews the origins and history of these ideas and uses modern data to highlight the current and growing controversy surrounding the validity and general applicability of this paradigm.

Masculinised Behaviour of XY Females in a Mammal with Naturally Occuring Sex Reversal

Most sex differences in phenotype are controlled by gonadal hormones, but recent work on laboratory strain mice that present discordant chromosomal and gonadal sex showed that sex chromosome complement can have a direct influence on the establishment of sex-specific behaviours, independently from gonads. In this study, we analyse the behaviour of a rodent with naturally occurring sex reversal: the African pygmy mouse Mus minutoides, in which all males are XY, while females are of three types: XX, XX* or X*Y (the asterisk represents an unknown X-linked mutation preventing masculinisation of X*Y embryos). X*Y females show typical female anatomy and, interestingly, have greater breeding performances. We investigate the link between sex chromosome complement, behaviour and reproductive success in females by analysing several behavioural features that could potentially influence their fitness: female attractiveness, aggressiveness and anxiety. Despite sex chromosome complement was not found to impact male mate preferences, it does influence some aspects of both aggressiveness and anxiety: X^*Y females are more aggressive than the XX and XX*, and show lower anxiogenic response to novelty, like males. We discuss how these behavioural differences might impact the breeding performances of females, and how the sex chromosome complement could shape the differences observed.

The time interval between sequential mating affects the response of male meadow voles to previous mates

Male meadow voles differed in their copulatory behaviour, mating and reproductive success, and odour preferences for successively encountered mates, when the interval between pairing with two females was 1 h, 1 day, 4 days, 7 days or 10 days. Male voles had shorter latencies to first ejaculation with female 2 than with female 1 when the interval was 1 h, which may be attributed to heightened sexual arousal in males for female 2. Males also had shorter copulatory bouts with female 2 than with female 1 when the intervals between pairings were 1 h and 1 day. Shorter copulation bouts may allow more mating opportunities for both sexes and encourage multiple mating. Male voles also preferred the scent marks of female 2 to those of female 1 when the interval between pairing was 7 or 10 days, suggesting that these females were treated as distinct entities.

Free mate choice enhances conservation breeding in the endangered giant panda

Conservation breeding programmes have become an increasingly important tool to save endangered species, yet despite the allocation of significant resources, efforts to create self-sustaining populations have met with limited success. The iconic giant panda (Ailuropoda melanoleuca) embodies the struggles associated with ex situ species conservation. Here we show that behavioural mate preferences in giant pandas predict reproductive outcomes. Giant pandas paired with preferred partners have significantly higher copulation and birth rates. Reproductive rates increase further when both partners show mutual preference for one another. If managers were to incorporate mate preferences more fully into breeding management, the production of giant panda offspring for China's reintroduction programme might be greatly expedited. When extended to the increasing numbers of species dependent on ex situ conservation breeding to avoid extinction, our findings highlight that mate preference and other aspects of informed behavioural management could make the difference between success and failure of these programmes.

Ex situ conservation breeding programmes for endangered species are expensive, and not always guaranteed to succeed. Here, Martin-Wintle et al. show that when captive giant pandas are given the opportunity to choose their preferred mate, copulation and birth rates increase significantly.

Fitness Benefits of Mate Choice for Compatibility in a Socially Monogamous Species

Research on mate choice has primarily focused on preferences for quality indicators, assuming that all individuals show consensus about who is the most attractive. However, in some species, mating preferences seem largely individual-specific, suggesting that they might target genetic or behavioral compatibility. Few studies have quantified the fitness consequences of allowing versus preventing such idiosyncratic mate choice. Here, we report on an experiment that controls for variation in overall partner quality and show that zebra finch (Taeniopygia guttata) pairs that resulted from free mate choice achieved a 37% higher reproductive success than pairs that were forced to mate. Cross-fostering of freshly laid eggs showed that embryo mortality (before hatching) primarily depended on the identity of the genetic parents, whereas offspring mortality during the rearing period depended on foster-parent identity. Therefore, preventing mate choice should lead to an increase in embryo mortality if mate choice targets genetic compatibility (for embryo viability), and to an increase in offspring mortality if mate choice targets behavioral compatibility (for better rearing). We found that pairs from both treatments showed equal rates of embryo mortality, but chosen pairs were better at raising offspring. These results thus support the behavioral, but not the genetic, compatibility hypothesis. Further exploratory analyses reveal several differences in behavior and fitness components between "free-choice" and "forced" pairs.

Female partner preferences enhance offspring ability to survive an infection

Background

It is often suggested that mate choice enhances offspring immune resistance to infectious diseases. To test this hypothesis, we conducted a study with wild-derived house mice (Mus musculus musculus) in which females were experimentally mated either with their preferred or non-preferred male, and their offspring were infected with a mouse pathogen, Salmonella enterica (serovar Typhimurium).

Results

We found that offspring sired by preferred males were significantly more likely to survive the experimental infection compared to those sired by non-preferred males. We found no significant differences in the pathogen clearance or infection dynamics between the infected mice, suggesting that offspring from preferred males were better able to cope with infection and had improved tolerance rather than immune resistance.

Conclusion

Our results provide the first direct experimental evidence within a single study that partner preferences enhance offspring resistance to infectious diseases.

Sexual selection against natural hybrids may contribute to reinforcement in a house mouse hybrid zone

Sexual selection may hinder gene flow across contact zones when hybrid recognition signals are discriminated against. We tested this hypothesis in a unimodal hybrid zone between Mus musculus musculus and Mus musculus domesticus where a pattern of reinforcement was described and lower hybrid fitness documented. We presented mice from the border of the hybrid zone with a choice between opposite sex urine from the same subspecies versus hybrids sampled in different locations across the zone. While no preference was evidenced in domesticus mice, musculus males discriminated in favour of musculus signals and against hybrid signals. Remarkably, the pattern of hybrid unattractiveness did not vary across the hybrid zone. Moreover, allopatric populations tested in the same conditions did not discriminate against hybrid signals, indicating character displacement for signal perception or preference. Finally, habituation-discrimination tests assessing similarities between signals pointed out that hybrid signals differed from the parental ones. Overall, our results suggest that perception of hybrids as unattractive has evolved in border populations of musculus after the secondary contact with domesticus. We discuss the mechanisms involved in hybrid unattractiveness, and the potential impact of asymmetric sexual selection on the hybrid zone dynamics and gene flow between the two subspecies.

Rapid adaptation to mammalian sociality via sexually selected traits

BACKGROUND

Laboratory studies show that the components of sexual selection (e.g., mate choice and intrasexual competition) can profoundly affect the development and fitness of offspring. Less is known, however, about the total effects of sexual selection on offspring in normal social conditions. Complex social networks, such as dominance hierarchies, regulate the opportunity for mating success, and are often missing from laboratory studies. Social selection is an extended view of sexual selection that incorporates competition during sexual and nonsexual interactions, and predicts complex evolutionary dynamics. Whether social selection improves or constrains offspring fitness is controversial.

RESULTS

To identify fitness consequences of social selection, wild-derived mice that had bred under laboratory conditions for eight generations were re-introduced to naturalistic competition in enclosures for three consecutive generations (promiscuous line). In parallel, a control lineage bred in cages under random mate assignment (monogamous line). A direct competition experiment using second-generation animals revealed that promiscuous line males had greater reproductive success than monogamous line males (particularly during extra-territorial matings), in spite of higher mortality and equivalent success in social dominance and sperm competition. There were no major female fitness effects (though promiscuous line females had fewer litters than monogamous line females). This result suggested that selection primarily acted upon a sexually attractive male phenotype in the promiscuous line, a hypothesis we confirmed in female odor and mating preference trials.

CONCLUSIONS

We present novel evidence for the strength of sexual selection under normal social conditions, and show rapid male adaptation driven largely by sexual trait expression, with tradeoffs in survivorship and female fecundity. Re-introducing wild-derived mice to competition quickly uncovers sexually selected phenotypes otherwise lost in normal colony breeding.

Paternal imprinting of mating preferences between natural populations of house mice (Mus musculus domesticus)

The evolutionary divergence of cues for mate recognition can contribute to early stages of population separation. We compare here two allopatric populations of house mice (Mus musculus domesticus) that have become separated about 3000 years ago. We have used paternity assignments in semi-natural environments to study the degree of mutual mate recognition according to population origin under conditions of free choice and overlapping generations. Our results provide insights into the divergence of mating cues, but also for the mating system of house mice. We find frequent multiple mating, occurrence of inbreeding and formation of extended family groups. In addition, many animals show strong mate fidelity, that is, frequent choice of the same mating partners in successive breeding cycles, indicating a role for familiarity in mating preference. With respect to population divergence, we find evidence for assortative mating, but only under conditions where the animals had time to familiarize themselves with mating partners from their own population. Most interestingly, the first-generation offspring born in the enclosure showed a specific mating pattern. Although matings between animals of hybrid population origin with animals of pure population origin should have occurred with equal frequency with respect to matching the paternal or maternal origin, paternal matching with mates from their own populations occurred much more often. Our findings suggest that paternally imprinted cues play a role in mate recognition between mice and that the cues evolve fast, such that animals of populations that are separated since not more than 3000 years can differentially recognize them.

Role of familiarity and preference in reproductive success in ex situ breeding programs

Success of captive-breeding programs centers on consistent reproduction among captive animals. However, many individuals do not reproduce even when they are apparently healthy and presented with mates. Mate choice can affect multiple parameters of reproductive success, including mating success, offspring production, offspring survival, and offspring fecundity. We investigated the role of familiarity and preference on reproductive success of female Columbia Basin pygmy rabbits (Brachylagus idahoensis) as measured by litter production, litter size, average number of young that emerged from the burrow, and average number of young that survived to 1 year. We conducted these studies on pygmy rabbits at the Oregon Zoo (Portland, Oregon, U.S.A.) and Washington State University (Pullman, Washington, U.S.A.) from February to June 2006, 2007, and 2008. Before mating, we housed each female adjacent to 2 males (neighbors). Female preference for each potential mate was determined on the basis of behavioral interactions observed and measured between the rabbits. We compared reproductive success between females mated with neighbor and non-neighbor males and between females mated with preferred and nonpreferred males. Our findings suggest that mating with a neighbor compared with a non-neighbor and mating with a preferred neighbor compared with a nonpreferred neighbor increased reproductive success in female pygmy rabbits. Litter production, average number of young that emerged, and average number of young that survived to 1 year were higher in rabbits that were neighbors before mating than in animals who were not neighbors. Pairing rabbits with a preferred partner increased the probability of producing a litter and was significantly associated with increased litter size. In captive breeding programs, mates are traditionally selected on the basis of genetic parameters to minimize loss of genetic diversity and inbreeding coefficients. Our results suggest that integrating genetic information with social dynamics and behavioral measures of preference may increase the reproductive output of the pygmy rabbit captive-breeding program. Our findings are consistent with the idea that allowing mate choice and familiarity increase the reproductive success of captive-breeding programs for endangered species.

Estrogenic involvement in social learning, social recognition and pathogen avoidance

Sociality comes with specific cognitive skills that allow the proper processing of information about others (social recognition), as well as of information originating from others (social learning). Because sociality and social interactions can also facilitate the spread of infection among individuals the ability to recognize and avoid pathogen threat is also essential. We review here various studies primarily from the rodent literature supporting estrogenic involvement in the regulation of social recognition, social learning (socially acquired food preferences and mate choice copying) and the recognition and avoidance of infected and potentially infected individuals. We consider both genomic and rapid estrogenic effects involving estrogen receptors α and β, and G-protein coupled estrogen receptor 1, along with their interactions with neuropeptide systems in the processing of social stimuli and the regulation and expression of these various socially relevant behaviors.

Behavioral evaluation of quinestrol as a sterilant in male Brandt's voles

The theoretical, ecological, physiological, and mathematical aspects of fertility control in mammals have already been well studied, but little attention has been given to the behavioral effects, especially in rodents. We investigated the effects of quinestrol, a synthetic estradiol analog, on social behavior and reproductive physiology in male Brandt's voles (Lasiopodomys brandtii). Over seven successive days, four concentration gradients of quinestrol (none, 0.001%, 0.003%, and 0.006%) were separately mixed into feed and provided to male Brandt's voles. Reproductive parameters, including the reproductive organ indexes, testosterone level and reproductive ability, were observed and collected 2 weeks after finished feeding treatment and again after 4 weeks. Dyadic social encounters and female preferences were then recorded for the control males (no quinestrol) and the highest concentration group (0.006%). Results showed that quinestrol reduced the consumption of feed. Physiological data revealed that quinestrol had also effectively reduced the reproductive organs indexes, testosterone levels, female pregnancy rates and litter size. This phenomenon was especially evident in the highest concentration group only after 2 weeks of feeding. Behavioral results showed that both frequency and duration of female preference were unbiased between control and treated males. In social conflict tests, control pairs (CC) had lower latency toward initial attack than treated pairs (TT) and pairs of one control and one treated male (CT). Among the three pairs, there was no evident difference in patterns of mutual attack and agonistic behavior. In CT pairs, sterile males have the same winning rate and agonistic behavior as control males. Our data revealed that quinestrol has anti-fertility capabilities with little behavioral side effects on Brandt's voles, which suggested quinestrol's potential as a sterilant for Brandt's voles. The palatability, however, should be improved before field practice.

The effects of breeding protocol in C57BL/6J mice on adult offspring behaviour

Animal experiments have demonstrated that a wide range of prenatal exposures can impact on the behaviour of the offspring. However, there is a lack of evidence as to whether the duration of sire exposure could affect such outcomes. We compared two widely used methods for breeding offspring for behavioural studies. The first involved housing male and female C57Bl/6J mice together for a period of time (usually 10–12 days) and checking for pregnancy by the presence of a distended abdomen (Pair-housed; PH). The second involved daily introduction of female breeders to the male homecage followed by daily checks for pregnancy by the presence of vaginal plugs (Time-mated; TM). Male and female offspring were tested at 10 weeks of age on a behavioural test battery including the elevated plus-maze, hole board, light/dark emergence, forced swim test, novelty-suppressed feeding, active avoidance and extinction, tests for nociception and for prepulse inhibition (PPI) of the acoustic startle response. We found that length of sire exposure (LSE) had no significant effects on offspring behaviour, suggesting that the two breeding protocols do not differentially affect the behavioural outcomes of interest. The absence of LSE effects on the selected variables examined does not detract from the relevance of this study. Information regarding the potential influences of breeding protocol is not only absent from the literature, but also likely to be of particular interest to researchers studying the influence of prenatal manipulations on adult behaviour.

Preference status does not indicate intrinsic quality differences in Drosophila pseudoobscura

The good genes hypothesis states that choosers prefer individuals of high intrinsic quality to individuals of lower intrinsic quality. Variation in longevity is thought to reflect, in part, intrinsic quality differences of individuals in addition to the costs of mating and reproduction. Here we report longevity variation of Drosophila pseudoobscura, a species in which previous experiments have demonstrated that individual mate preferences (pre-touching mate assessments) of females and males are associated with enhanced numbers of eclosed (adult) offspring and higher egg-to-adult survival (offspring viability). Using mate assessment arenas and protocols similar to those in a previous experiment that demonstrated fitness benefits to breeders and their offspring of mating with individuals they preferred, we tested the following predictions: (i) preferred discriminatees live longer than non-preferred discriminatees; (ii) males live longer than females; and (iii) virgins live longer than mated individuals. The experiment yielded 938 individuals for longevity analysis. Sex and mating status affected longevity: males lived longer than females, virgin females lived longer than mated females, but there were no differences in longevity for mated and virgin males. Non-preferred discriminatees of both sexes survived as long as preferred discriminatees, a result inconsistent with the prediction of the good genes hypothesis for mate preferences. To our knowledge, this is the first demonstration of the cost of reproduction for females in D. pseudoobscura and of longevity variation of preferred and non-preferred discriminatees.

Female prairie vole mate-choice is affected by the males' birth litter composition

Experimental testing and retrospective examination of breeding records were used to examine the influence of sex composition and/or size of males' birth litters on female mate-choice. Sexually naïve female prairie voles (Microtus ochrogaster) avoided males derived from all-male litters, but showed no preference for, or aversion to, males from single-male litters or from more typical mixed-sex litters. Examination of the pregnancy status of females after two weeks of pairing with a male allowed us to estimate the probabilites of a pups' intrauterine position relative to siblings for various litter sizes. The typical prairie vole pup derived from a mixed-sex litter comprised of 4.4 pups, and had a 13% chance of being isolated from siblings in utero and a 22% chance of being between siblings in utero. Pups from single-sex litters tended to be larger at weaning than did pups from mixed-sex litters; however, male size did not influence female choice behavior. These results suggest that some aspect of the perinatal experience of prairie vole pups from single sex litters can influence social interactions later in life.

Reproductive compensation in broad-nosed pipefish females

The differential allocation hypothesis assumes that animals should weigh costs and benefits of investing into reproduction with a current mate against the expected quality of future mates, and predicts that they should invest more into reproduction when pairing with a high-quality mate. In the broad-nosed pipefish (Syngnathus typhle), males care for the embryos in a brood pouch and females compete for access to male mating partners. Both sexes prefer mating with large partners. In the present study, we show that the same female provides both large and small mating partners with eggs of similar size, weight and lipid content when mated to two males in succession. Importantly, however, eggs provided to small males (less preferred) had higher egg protein content (11% more) than those provided to large males (preferred). Thus, contrary to the differential allocation hypothesis, eggs did not contain more resources when females mated with a larger male. Instead, the pattern observed in our results is consistent with a compensatory reproductive strategy.