Female calls in lek-mating birds: indirect mate choice, female competition for mates, or direct mate choice?

I tested predictions from ultimate hypotheses of why femalegreat snipe Gallinago media give loud calls when visiting leks,using observational data and playback experiments. One hypothesisis that calls might be used in female—female competitionfor popular males, either (1) in an aggressive context towarda specific female, or (2) toward females in general to defendthe male. It has also been suggested that female calls (3) may not have an adaptive function, the capability of vocalizingbeing explained as a correlated response to selection on malesinging. Further, calls might function as (4) a copulationsolicitation toward a specific male. Finally, calls might havea function in mate choice, either (5) in indirect mate choiceas a fertility advertisement to incite male fighting, or (6)in direct mate choice as a mate-sampling aid to provoke quality-revealing responses from males. Disproportionately many female calls wereuttered when no other females were present on a male's territoryand in territories of males without mating success, contradictinghypotheses 1 and 2. Female calls were not associated with copulation;calls generally occurred several days before copulations, contradictinghypotheses 4 and 5. Playback of female calls attracted malesand increased fighting among males, even if females were presentnearby, contradicting hypothesis 3. Males changed their ownsongs in response to playback, and the response was relatedto their mating success. Taken together, the results are onlyconsistent with one of the hypotheses considered—femalecalls may function as a mate-sampling aid used in direct matechoice.     

Demonstrating mate choice copying in spiders requires further research

Mate choice copying-when individuals learn to prefer mates or mate types that have been chosen by others-can influence trait evo-lution and speciation(Varela et al.2018;Dion et al.2019).Most examples of mate choice copying are from fish,birds,and mammals including humans(Varela et al.2018).However,2 invertebrate examples-fruit flies and wolf spiders-have been used to argue that the phenomenon may be phylogenetically widespread,and perhaps the rule rather than the exception in nature(Varela et al.2018).Here,we revisit the evidence for mate choice copying in wolf spiders(Fowler-Fimn et al.2015)in light of new data(Gilman et al.2018).Then,we discuss why mate choice copying is a phenomenon that is likely to occur in wolf spiders,and why this deserves attention.     

Should females prefer to mate with low-quality males?

We analyse a model of mate choice when males differ in reproductive quality and provide care for their offspring. Females choose males on the basis of the success they will obtain from breeding with them and a male chooses his care time on the basis of his quality so as to maximise his long-term rate of reproductive success. We use this model to establish whether high-quality males should devote a longer period of care to their broods than low-quality males and whether females obtain greater reproductive success from mating with higher quality males. We give sufficient conditions for optimal care times to decrease with increasing male quality. When care times decrease, this does not necessarily mean that high-quality males are less valuable to the female because quality may more than compensate for the lack of care. We give a necessary and sufficient condition for high-quality males to be less valuable mates, and hence for females to prefer low-quality males. Females can prefer low-quality males if offspring produced and cared for by high-quality males do well even if care is short, and do not significantly benefit from additional care, while offspring produced and cared for by low-quality males do well only if they receive a long period of care.     

Why do pied flycatcher females mate with already-mated males?

The contribution of the pied flycatcher Ficedula hypoleuca male in parental care was studied to examine why some females mate with already-mated males. No difference in feeding rate was found between older and yearling monogamous males, when comparing nests at the same time. Monogamous and primary females were helped significantly more in parental care by the male than were secondary females of polygynous males. Females could only partly compensate for the absence of a male and of nestlings were reduced in nests with low male assistance. Differences in mate and territory quality were far too slight to make it advantageous for females to choose already-mated males instead of mating with monogamous males. We suggest that males, by being polyterritorial, deceive females into accepting polygyny; and females can be deceived since they do not have time to find out the marital status of males.     

How is female mate choice affected by male competition?

The plethora of studies devoted to the topics of male competition and female mate choice belie the fact that their interaction remains poorly understood. Indeed, on the question of whether competition should help or hinder the choice process, opinions scattered throughout the sexual selection literature seem unnecessarily polarised. We argue, in the light of recent theoretical and empirical advances, that the effect of competition on mate choice depends on whether it results in the choosy sex attaining high breeding value for total fitness, considering both direct and indirect fitness benefits. Specifically, trade-offs may occur between different fitness benefits if some are correlated with male competitive ability whilst others are not. Moreover, the costs and benefits of mating with competitive males may vary in time and/or space. These considerations highlight the importance of injecting a life-history perspective into sexual selection studies. Within this context, we turn to the sexual selection literature to try to offer insights into the circumstances when competition might be expected to have positive or negative implications for pre-copulatory female choice. In this regard, we elaborate on three stages where competition might impact upon the choice process: (i) during mate detection, (ii) mate evaluation, and (iii) in dictating actual mating outcomes. We conclude by offering researchers several potentially rewarding avenues for future research.     

Do malaria parasites mate non-randomly in the mosquito midgut?

Polymerase chain reaction (PCR)-based genotyping of oocysts dissected from mosquito midguts has previously been used to investigate overall levels of inbreeding within malaria parasite populations. We present a re-analysis of the population structure of Plasmodium falciparum malaria using diploid genotypes at three antigen-encoding loci in 118 oocysts dissected from 34 mosquitoes. We use these data to ask whether mating is occurring at random within the mosquito midgut, as is generally assumed. We observe a highly significant deficit of heterozygous oocysts within mosquitoes at all three loci, suggesting that fusion of gametes occurs non-randomly in the mosquito gut. A variety of biological explanations, such as interrupted feeding of mosquitoes, positive assortative mating and outcrossing depression, could account for this observation. However, an alternative artefactual explanation--the presence of non-amplifying or null alleles--can account for the observed data equally well, without the need to invoke non-random mating. To evaluate this explanation further, we estimate the frequencies of null alleles within the oocyst population using maximum likelihood, by making the assumption that non-amplifying oocysts at any of the three loci are homozygous for null alleles. Observed levels of visible heterozygotes fit closely with those expected under random mating when non-amplifying oocysts are accounted for. Other lines of evidence also support the artefactual explanation. Overall inbreeding coefficients have been recalculated in the light of this analysis, and may be considerably lower than those estimated previously. In conclusion, we suggest that the deficit of heterozygotes observed is unlikely to indicate non-random mating within the mosquito gut and is better explained by misscoring of heterozygotes as homozygotes.     

Social behavior: how do fish find their shoal mate?

Fish form social aggregations called shoals which often consist of fish with similar morphologies. Experiments using zebrafish pigment variants demonstrate that fish can select shoal mates solely on the basis of their color patterns, and that early experience plays a key role in determining these shoaling preferences.     

Why do females mate multiply? A review of the genetic benefits

The aim of this review is to consider the potential benefits that females may gain from mating more than once in a single reproductive cycle. The relationship between non-genetic and genetic benefits is briefly explored. We suggest that multiple mating for purely non-genetic benefits is unlikely as it invariably leads to the possibility of genetic benefits as well. We begin by briefly reviewing the main models for genetic benefits to mate choice, and the supporting evidence that choice can increase offspring performance and the sexual attractiveness of sons. We then explain how multiple mating can elevate offspring fitness by increasing the number of potential sires that compete, when this occurs in conjunction with mechanisms of paternity biasing that function in copula or post-copulation. We begin by identifying cases where females use pre-copulatory cues to identify mates prior to remating. In the simplest case, females remate because they identify a superior mate and 'trade up' genetically. The main evidence for this process comes from extra-pair copulation in birds. Second, we note other cases where pre-copulatory cues may be less reliable and females mate with several males to promote post-copulatory mechanisms that bias paternity. Although a distinction is drawn between sperm competition and cryptic female choice, we point out that the genetic benefits to polyandry in terms of producing more viable or sexually attractive offspring do not depend on the exact mechanism that leads to biased paternity. Post-copulatory mechanisms of paternity biasing may: (1) reduce genetic incompatibility between male and female genetic contributions to offspring; (2) increase offspring viability if there is a positive correlation between traits favoured post-copulation and those that improve performance under natural selection; (3) increase the ability of sons to gain paternity when they mate with polyandrous females. A third possibility is that genetic diversity among offspring is directly favoured. This can be due to bet-hedging (due to mate assessment errors or temporal fluctuations in the environment), beneficial interactions between less related siblings or the opportunity to preferentially fertilise eggs with sperm of a specific genotype drawn from a range of stored sperm depending on prevailing environmental conditions. We use case studies from the social insects to provide some concrete examples of the role of genetic diversity among progeny in elevating fitness. We conclude that post-copulatory mechanisms provide a more reliable way of selecting a genetically compatible mate than pre-copulatory mate choice. Some of the best evidence for cryptic female choice by sperm selection is due to selection of more compatible sperm. Two future areas of research seem likely to be profitable. First, more experimental evidence is needed demonstrating that multiple mating increases offspring fitness via genetic gains. Second, the role of multiple mating in promoting assortative fertilization and increasing reproductive isolation between populations may help us to understand sympatric speciation.     

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

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

Gender differences in mate selection criteria: Sociobiological or socioeconomic explanation?

Past research has demonstrated clear gender differences in reported mate selection criteria. Compared to women, men place more importance on physical attractiveness and women place more importance than men do on the earning capacity of a potential mate. These gender differences have been explained using both sociobiological propositions and differences in the relative economic power of men and women. The present study tested the structural powerlessness hypothesis as an explanation for women's greater emphasis on the earning capacity of a potential spouse. Samples of college students (N = 997) and community members (N = 282) were asked to report expected personal income and to rate the importance of listed characteristics in a potential mate. Consistent with past research, men placed more emphasis on the item Good Looks, whereas women placed more importance on the item Good Financial Prospect. Contrary to the structural powerless model, women's expected income was positively related to ratings of the importance of a potential mate's earning capacity in the college sample and was unrelated to women's ratings of the item Good Financial Prospect in the community sample. Findings are discussed in terms of both evolutionary psychology and gender differences in access to financial resources.     

Why do territorial male Tengmalm's owls fail to obtain a mate?

Non-breeding may occur because non-breeders are immature or somehow physiologically incapable of breeding, or because of a lack of resources (e.g. food resources, mating partners) needed to breed. There is, however, a lack of experimental evidence on whether bachelor males possessing territories and nest-sites are able to breed when supplemented with extra food or provided with mating partners. In vole-eating Tengmalm's owl, Aegolius funereus, we provided supplementary food and transferred females in nest-boxes of non-breeding males. Bachelor males that we supplemented with food did not attract mates at a higher frequency than unfed control males, which suggests that a lack of food did not influence the ability to attract a mating partner. In contrast, bachelor males presented with a female seemed to breed more frequently than bachelor males in the control group without mate addition. This suggests that scarcity of females may be an important reason for the high proportion of non-breeding males in the population (c. 25%) and excludes the possibility that non-breeding males are physiologically unable to breed. The operational sex ratio of the owl population at the time of mating may be male-biased, and some males may thus remain unpaired. Habitat and nest-box quality also seemed to be lower among bachelors than among breeding males. Received: 22 September 1997 / Accepted: 29 December 1997     

Can cytoplasmic incompatibility inducing Wolbachia promote the evolution of mate preferences?

The maternally inherited bacterium, Wolbachia pipientis, manipulates host reproduction by rendering uninfected females reproductively incompatible with infected males (cytoplasmic incompatibility, CI). Hosts may evolve mechanisms, such as mate preferences, to avoid fitness costs of Wolbachia infection. Despite the potential importance of mate choice for Wolbachia population dynamics, this possibility remains largely unexplored. Here we model the spread of an allele encoding female mate preference for uninfected males alongside the spread of CI inducing Wolbachia. Mate preferences can evolve but the spread of the preference allele depends on factors associated with both Wolbachia infection and the preference allele itself. Incomplete maternal transmission of Wolbachia, fitness costs and low CI, improve the spread of the preference allele and impact on the population dynamics of Wolbachia. In addition, mate preferences are found in infected individuals. These results have important consequences for the fate of Wolbachia and studies addressing mate preferences in infected populations.     

Divergence in mate choice systems: does evolution play by rules?

Understanding the genetic bases of phenotypes associated with the earliest stages of divergence will reveal a great deal about species formation. I review a number of model systems, most involving plant–insect interactions, that have already revealed genetic aspects of incipient speciation. It is suggested that progress in understanding the causal forces driving mating signal evolution and incipient speciation will be expedited in model systems where; (1) ecological and evolutionary information is available, (2) different aspects of mating behaviors that function in mate and/or species recognition are known, (3) genetic analysis of single phenotypes is undertaken, (4) analysis of sexual selection and isolation is performed under natural conditions (or in the wild), and (5) comparative data from related species are available to assess phylogenetic trends.     

Is mate fidelity related to site fidelity? A comparative analysis in Ciconiiforms

We tested for an association between divorce rate and site fidelity in 42 avian species belonging to the order Ciconiiforms, using comparative methods that account for the influences of phylogenetic relationships on the data. Our methods enabled us to detect evidence of correlated evolution and provided information on the temporal ordering of evolutionary changes in these two variables. We found a significant correlation between divorce rate and site fidelity, indicating that species with little or no site fidelity are more likely to divorce. Our data suggest that the coupled evolution of divorce and site fidelity can be summarized by three major events. The first event corresponds to a transition from species showing high divorce rate and low or no site fidelity to species that tended to reuse the same nests over consecutive breeding seasons. This was followed by a transition towards higher mate fidelity, with the preservation of pair bonds over consecutive breeding attempts. In a third stage, divorce rate and the rate of site fidelity varied, independently of each other. We discuss our results within the context of the ancestor species and the past environments in which the traits originated, and address the importance of the potential for individual recognition in shaping the observed patterns of covariation between mate fidelity and site fidelity in Ciconiiforms. Copyright 2000 The Association for the Study of Animal Behaviour.     

(Under)water love-linking mate choice and cognition in fish and frogs

Aims and Objectives This Special Column aims at complementing our knowledge and deepening our understanding of the complex processes involved in learning and neurobiological mechanisms in the context of sexual selection.     

Territorial behavior in Southeast Asian langurs: Resource defense or mate defense?

Between-group antagonism or territoriality in primates may serve two different but compatible functions: resource defense or mate defense. Females are expected to be involved more strongly in the first, males in the second. The resource defense hypothesis predicts that home range overlap should decrease as defensibility and population density increase, and that females should be involved in hostile between-group interactions. The mate defense hypothesis predicts that between-group relations should be hostile and that males should take the primary role in antagonistic encounters. In a comparative study of 12 populations of 6 Presbytis species in Southeast Asia, we found support for the mate defense hypothesis; only males produce loud calls, between-group antagonism is entirely a male affair, and neither defensibility nor population density determine spatial exclusivity or the level of antagonism. We discuss the differences between our findings and traditional interpretations of territorial behavior.