A role of her own: female cowbirds, Molothrus ater, influence the development and outcome of song learning

Previous work has shown that captive female cowbirds, Molothrus ater, can influence the outcome of male song development by affecting retention or deletion of song elements and by stimulating improvization. Here we looked for evidence of female influence during the process of learning, as males progress from subsong to plastic song to stereotyped song. In a longitudinal study, we measured the rate and timing of vocal development in captive, juvenile male brown-headed cowbirds, M. a. artemisiae. Half the young males were housed with female cowbirds from their own population (South Dakota: SD) and half with female cowbirds from a M. a. ater population (Indiana: IN). Both populations of females prefer local songs and differ in the time of breeding, with SD females breeding 2 weeks later than IN females. The results showed significant effects of female presence on the age at which males advanced through stages of vocal development: the SD males with SD females, as opposed to SD males with IN females, developed stereotyped song earlier, reduced motor practise earlier, and produced more effective playback songs. Longitudinal observations of social interactions showed that the two groups of females reliably differed in social responses to males. Degree of social proximity of females to males in the winter predicted song maturity, rate of rehearsal and song potency. Thus, females can stimulate the progression of song learning, as well as prune song content. Copyright 2000 The Association for the Study of Animal Behaviour.     

Independent Mating Preferences for Male Body Size and Coloration in Female Trinidadian Guppies

Although females in numerous species generally prefer males with larger, brighter and more elaborate sexual traits, there is nonetheless considerable intra‐ and interpopulation variation in mating preferences amongst females that requires explanation. Such variation exists in the Trinidadian guppy, Poecilia reticulata, an important model organism for the study of sexual selection and mate choice. While female guppies tend to prefer more ornamented males as mates, particularly those with greater amounts of orange coloration, there remains variation both in male traits and female mating preferences within and between populations. Male body size is another trait that is sexually selected through female mate choice in some species, but has not been examined as extensively as body coloration in the guppy despite known intra‐ and interpopulation variation in this trait among adult males and its importance for survivorship in this species. In this study, we used a dichotomous‐choice test to quantify the mating preferences of female guppies, originating from a low‐predation population in Trinidad, for two male traits, body length and area of the body covered with orange and black pigmentation, independently of each other. We expected strong female mating preferences for both male body length and coloration in this population, given relaxation from predation and presumably relatively low cost of choice. Females indeed exhibited a strong preference for larger males as expected, but surprisingly a weaker (but nonetheless significant) preference for orange and black coloration. Interestingly, larger females demonstrated stronger preferences for larger males than did smaller females, which could potentially lead to size‐assortative mating in nature.     

Sexual selection and assortative mating: an experimental test

Mate choice and mate competition can both influence the evolution of sexual isolation between populations. Assortative mating may arise if traits and preferences diverge in step, and, alternatively, mate competition may counteract mating preferences and decrease assortative mating. Here, we examine potential assortative mating between populations of Drosophila pseudoobscura that have experimentally evolved under either increased (‘polyandry’) or decreased (‘monogamy’) sexual selection intensity for 100 generations. These populations have evolved differences in numerous traits, including a male signal and female preference traits. We use a two males: one female design, allowing both mate choice and competition to influence mating outcomes, to test for assortative mating between our populations. Mating latency shows subtle effects of male and female interactions, with females from the monogamous populations appearing reluctant to mate with males from the polyandrous populations. However, males from the polyandrous populations have a significantly higher probability of mating regardless of the female's population. Our results suggest that if populations differ in the intensity of sexual selection, effects on mate competition may overcome mate choice.     

Mate choice opportunity leads to shorter offspring development time in a desert insect

We describe indirect genetic benefits of mate choice in two allopatric populations of cactophilic Drosophila mojavensis. By manipulating mate choice opportunity, we show that greater mate choice among sexually mature adults leads to shorter offspring egg-to-adult development times; the extent of this reduction was influenced by population origin and by host plant environment. We performed multiple-choice mating trials with individually marked flies to investigate whether differential male mating success was a consequence of female choice, male interaction, or both. We demonstrate that male copulation frequency was not random and instead, was determined by female choice. Virgin females in these trials were no less discriminating than females that had been previously exposed to males. These results suggest that there are indirect benefits of female mate choice that are population and environment specific, consistent with the hypothesis of ecologically influenced 'good genes' sexual selection.     

Fitness effects of female mate choice: preferred males are detrimental for Drosophila melanogaster females

The evolution of female mate choice, broadly defined to include any female behaviour or morphology which biases matings towards certain male phenotypes, is traditionally thought to result from direct or indirect benefits which females acquire when mating with preferred males. In contrast, new models have shown that female mate choice can be generated by sexual conflict, where preferred males may cause a fitness depression in females. Several studies have shown that female Drosophila melanogaster bias matings towards large males. Here, we use male size as a proxy for male attractiveness and test how female fitness is affected by reproducing with large or small males, under two different male densities. Females housed with large males had reduced lifespan and aged at an accelerated rate compared with females housed with small males, and increased male density depressed female fitness further. These fitness differences were due to effects on several different fitness components. Female fitness covaried negatively with male courtship rate, which suggests a cost of courtship. Mating rate increased with male size, whereas female fitness peaked at an intermediate mating rate. Our results suggest that female mate choice in D. melanogaster is, at least in part, a by-product of sexual conflict over the mating rate.     

Female Mate Preferences Among Pan troglodytes schweinfurthii of Kanyawara, Kibale National Park, Uganda

Studies of reproduction among chimpanzees traditionally have focused on the mating strategies of males. However, less is known about the mating strategies of female chimpanzees and whether they demonstrate mate choice. I investigated sexual behavior and female mate preference in the chimpanzees of the Kanyawara community. To estimate mate preferences, I analyzed female proceptivity and resistance rates of 6 estrous females toward a total of 13 males as well as male solicitation and aggression rates toward females. Males solicited some females more often than others for mating and preferred them throughout estrus, not only during the periovulatory period (POP), when conception was most likely. In contrast, though females had strong mate preferences in both non-POP and POP, their mate preferences were not consistent between the 2 phases. The shift in mate preferences is evidence of a promiscuous yet tactical mating strategy to confuse paternity. Further, females were more proceptive and generally less resistant toward eschewed males in non-POP and more proceptive and less resistant toward preferred males in POP. Hence, the results indicate that females attempted to mate selectively during the fertile phase. Kanyawara female chimpanzees appear to change their mating strategies and selectivity during estrus and thus may pursue a mixed reproductive strategy. The tactic may allow females to deceive males, indicating that promiscuity among chimpanzee females may be more strategic than previously thought.     

When less is best: female brown-headed cowbirds prefer less intense male displays

Sexual selection theory predicts that females should prefer males with the most intense courtship displays. However, wing-spread song displays that male brown-headed cowbirds (Molothrus ater) direct at females are generally less intense than versions of this display that are directed at other males. Because male-directed displays are used in aggressive signaling, we hypothesized that females should prefer lower intensity performances of this display. To test this hypothesis, we played audiovisual recordings showing the same males performing both high intensity male-directed and low intensity female-directed displays to females (N?=?8) and recorded the females' copulation solicitation display (CSD) responses. All eight females responded strongly to both categories of playbacks but were more sexually stimulated by the low intensity female-directed displays. Because each pair of high and low intensity playback videos had the exact same audio track, the divergent responses of females must have been based on differences in the visual content of the displays shown in the videos. Preferences female cowbirds show in acoustic CSD studies are correlated with mate choice in field and captivity studies and this is also likely to be true for preferences elucidated by playback of audiovisual displays. Female preferences for low intensity female-directed displays may explain why male cowbirds rarely use high intensity displays when signaling to females. Repetitive high intensity displays may demonstrate a male's current condition and explain why these displays are used in male-male interactions which can escalate into physical fights in which males in poorer condition could be injured or killed. This is the first study in songbirds to use audiovisual playbacks to assess how female sexual behavior varies in response to variation in a male visual display.     

Does sexual experience affect the strength of male mate choice for high‐quality females in Drosophila melanogaster?

Although females are traditionally thought of as the choosy sex, there is increasing evidence in many species that males will preferentially court or mate with certain females over others when given a choice. In the fruit fly, Drosophila melanogaster, males discriminate between potential mating partners based on a number of female traits, including species, mating history, age, and condition. Interestingly, many of these male preferences are affected by the male''s previous sexual experiences, such that males increase courtship toward types of females that they have previously mated with and decrease courtship toward types of females that have previously rejected them. D. melanogaster males also show courtship and mating preferences for larger females over smaller females, likely because larger females have higher fecundity. It is unknown, however, whether this preference shows behavioral plasticity based on the male''s sexual history as we see for other male preferences. Here, we manipulate the sexual experience of D. melanogaster males and test whether this manipulation has any effect on the strength of male mate choice for large females. We find that sexually inexperienced males have a robust courtship preference for large females that is unaffected by previous experience mating with, or being rejected by, females of differing sizes. Given that female body size is one of the most common targets of male mate choice across insect species, our experiments with D. melanogaster may provide insight into how these preferences develop and evolve.     

The evolution of female mate choice by sexual conflict

Although empirical evidence has shown that many male traits have evolved via sexual selection by female mate choice, our understanding of the adaptive value of female mating preferences is still very incomplete. It has recently been suggested that female mate choice may result from females evolving resistance rather than attraction to males, but this has been disputed. Here, we develop a quantitative genetic model showing that sexual conflict over mating indeed results in the joint evolution of costly female mate choice and exaggerated male traits under a wide range of circumstances. In contrast to tradition explanations of costly female mate choice, which rely on indirect genetic benefits, our model shows that mate choice can be generated as a side-effect of females evolving to reduce the direct costs of mating.     

Secondary sexual ornamentation and non-additive genetic benefits of female mate choice

Ornamental secondary sexual traits are hypothesized to evolve in response to directional mating preferences for more ornamented mates. Such mating preferences may themselves evolve partly because ornamentation indicates an individual's additive genetic quality (good genes). While mate choice can also confer non-additive genetic benefits (compatible genes), the identity of the most 'compatible' mate is assumed to depend on the choosy individual's own genotype. It is therefore unclear how choice for non-additive genetic benefits could contribute to directional mating preferences and consequently the evolution of ornamentation. In free-living song sparrows (Melospiza melodia), individual males varied in their kinship with the female population. Furthermore, a male's song repertoire size, a secondary sexual trait, was negatively correlated with kinship such that males with larger repertoires were less closely related to the female population. After excluding close relatives as potential mates, individual females were on average less closely related to males with larger repertoires. Therefore, female song sparrows expressing directional preferences for males with larger repertoires would on average acquire relatively unrelated mates and produce relatively outbred offspring. Such non-additive genetic fitness benefits of directional mating preferences, which may reflect genetic dominance variance expressed in structured populations, should be incorporated into genetic models of sexual selection.     

Sexual selection and speciation in mammals,butterflies and spiders

Recently refined evolutionary theories propose that sexual selection and reproductive conflict could be drivers of speciation. Male and female reproductive optima invariably differ because the potential reproductive rate of males almost always exceeds that of females: females are selected to maximize mate 'quality', while males can increase fitness through mate 'quantity'. A dynamic, sexually selected conflict therefore exists in which 'competitive' males are selected to override the preference tactics evolved by 'choosy' females. The wide variation across taxa in mating systems therefore generates variance in the outcome of intrasexual conflict and the strength of sexual selection: monandry constrains reproductive heterozygosity and allows female choice to select and maintain particular (preferred) genes; polyandry promotes reproductive heterozygosity and will more likely override female choice. Two different theories predict how sexual selection might influence speciation. Traditional ideas indicate that increased sexual selection (and hence conflict) generates a greater diversity of male reproductive strategies to be counteracted by female mate preferences, thus providing elevated potentials for speciation as more evolutionary avenues of male-female interaction are created. A less intuitively obvious theory proposes that increased sexual selection and conflict constrains speciation by reducing the opportunities for female mate choice under polyandry. We use a comparative approach to test these theories by investigating whether two general measures of sexual selection and the potential for sexual conflict have influenced speciation. Sexual size dimorphism (across 480 mammalian genera, 105 butterfly genera and 148 spider genera) and degree of polyandry (measured as relative testes size in mammals (72 genera) and mating frequency in female butterflies (54 genera)) showed no associations with the variance in speciosity. Our results therefore show that speciation occurs independently of sexual selection.     

Genetic dissimilarity,genetic diversity,and mate preferences in humans

It is clear that genes at the major histocompatibility complex (MHC) are involved in mate preferences in a range of species, including humans. However, many questions remain regarding the MHC's exact influence on mate preference in humans. Some research suggests that genetic dissimilarity and individual genetic diversity (heterozygosity) at the MHC influence mate preferences, but the evidence is often inconsistent across studies. In addition, it is not known whether apparent preferences for MHC dissimilarity are specific to the MHC or reflect a more general preference for genome-wide dissimilarity, and whether MHC-related preferences are dependent on the context of mate choice (e.g., when choosing a short-term and long-term partner). Here, we investigated whether preferences for genetic dissimilarity are specific to the MHC and also whether preferences for genetic dissimilarity and diversity are context dependent. Genetic dissimilarity (number of alleles shared) influenced male, but not female, partner preferences, with males showing a preference for the faces of MHC-dissimilar females in both mating contexts. Genetic diversity [heterozygosity (H) and standardized mean (d²)] influenced both male and female preferences, regardless of mating context. Females preferred males with greater diversity at MHC loci (H) and males preferred females with greater diversity at non-MHC loci (d²) in both contexts. Importantly, these findings provide further support for a special role of the MHC in human sexual selection and suggest that male and female mate preferences may work together to potentially enhance both male and female reproductive success by increasing genetic diversity in offspring.     

Indications for female mate choice in grey-cheeked mangabeys <Emphasis Type="Italic">Lophocebus albigena johnstoni</Emphasis> in Kibale National Park,Uganda

Female sexual strategies affect male strategies and can play an important role in shaping mating systems. We investigated female sexual behaviour within five groups of grey-cheeked mangabeys in Kibale National Park, Uganda, and tested the hypothesis that females exhibit mate choice using as indications the prevalence of (1) females soliciting matings by presenting to males and (2) females refusing to mate with approaching males. In addition, we describe how these behaviours as well as grooming and copulation calls are distributed over high-ranking, low-ranking and migrating males and discuss these patterns with regard to trade-offs that could play a roll in female mate choice in multi-male groups. Females were promiscuous and initiated almost half of the matings, with both resident and migrating males. More than half of male mating approaches were refused by peak females. Female mate choice in this species may depend on individual female preferences, oestrus phase and male tactic.     

Female Cowbird Song Perception: Evidence for Plasticity of Preference

The goal of the research reported here was to look for evidence of modifiability of preference for male song in female cowbirds, Molothrus ater. To this end, we investigated whether social experience affected the breadth and consistency of females’ playback preferences for geographic variants of male song. In three experiments, we varied female cowbirds’ exposure to males. Wild‐caught juvenile females showed a preference for local song in their first year when housed without males in sound‐attenuating chambers, as we had found previously with adult females. But we found that neither adult nor juvenile females showed a preference for local over distant song after they had been housed in large, outdoor aviaries with other females but without male residents. Aviary housing with local males did lead to preferences for local songs. These data represent the first unqualified evidence that adult and juvenile female cowbird preferences for song are modifiable. These data add to the growing body of literature suggesting that receivers, as well as signalers, rely on learning during development of their communication system.     

A review of the potential of surface flow constructed wetlands to enhance macroinvertebrate diversity in agricultural landscapes with particular reference to Integrated Constructed Wetlands (ICWs)

Discriminating female mate preferences enhance the variance in reproductive success among males of a population and create a potential for sexual selection, which can account for trait evolution and diversification. Fish color patterns are among the prime targets of mate choice-driven sexual selection. Populations of the cichlid Tropheus from Lake Tanganyika display remarkable geographic color pattern variation, but the role of female choice in their rapid and rich phenotypic diversification is unclear. Males and females establish a pair bond prior to spawning monogamously, but as brood care is strictly maternal, female investment in reproduction is high and the operational sex ratio is male-biased. Therefore, variance in male reproductive success can accrue if individual males succeed repeatedly in securing a mate. To test this prediction in the red colored Tropheus moorii “Chimba”, four pairs of males were presented to a series of females and female mate preferences were inferred from pairwise interactions. There was a significant difference in mating success between the males of each pair (P < 0.001 over all trials), as—with one exception—females shared preferences for the same males. Male courtship activity was strongly correlated with female choice. Our experiment suggests that female choice contributes to the variance in male reproductive success in the tested population.     

Mate sampling and the sexual conflict over mating in seaweed flies

The order in which females encounter, or sample, males in apopulation may have important consequences for mate choice,with the information gathered about males influencing boththe preference function and degree of choosiness of females.Sexual selection may be affected as a result. Sampling of particularsubsets of males may be a crucial component of individual variation in mate preferences within populations. However, the sequencein which males are sampled may also be important in specieswithout traditional, active mate choice, such as when sexualselection involves sexual conflict over mating. This wouldoccur if the likelihood of a female mating with a male of acertain phenotype changes as a result of previous encounters.We examined the effects of encountering males differing inbody size, a sexually selected phenotype, in the seaweed flyCoelopa frigida. Sexual selection occurs in this species asa result of a sexual conflict over mating. We show that theoutcome of the sexual conflict is independent of the orderin which males are encountered by female seaweed flies, withthe overall mating advantage to large males being unaffected.In addition, we explored female preference functions and evaluatethe heterogeneity in female willingness to mate. We suggestthat consideration of mate sampling theory is valuable whenexamining mate choice in species in which sexual selectionis driven by sexual conflict.     

Female mating preference for own males on species and population level in Chromaphyosemion killifishes (Cyprinodontiformes, Nothobranchiidae)

Chromaphyosemion killifishes are a very promising taxon for the examination of general principles and mechanisms underlying speciation. The polygamous mating system and high degree of sexual dimorphism in this group suggest that sexual selection and female mating preferences play a crucial role in the current radiation process. Because the emergence of mating preferences for individuals of the own population during allopatry is a necessary precondition for speciation by sexual selection, either via diverging mate recognition traits or reinforcement, we examined whether females of different nominal species (Chromaphyosemion bivittatum vs. Chromaphyosemion volcanum) or populations (C. bivittatum “Toko” vs. C. bivittatum “Ilor”) prefer their own males as mating partners. For this purpose, two different methods were used. First, we conducted simultaneous choice tests where females could choose between two different males, and second, we counted the eggs produced by females in consecutive matings with different males. Both approaches produced the same result: females of the populations under examination preferred to mate with their own males. Preference for own males was symmetrical in all tests. Males, on the other hand, do not discriminate between females, not even on the level of nominal species. Thus, our results are in accordance with the hypothesis that female choice is an important factor for speciation in Chromaphyosemion. Additionally, we present some preliminary data on post-zygotic isolation between the populations.     

Age and experience affect female choice in the guppy (Poecilia reticulata)

Female choices of males, and how these choices are influenced by ecological and social factors, have been studied extensively. However, little is known about the effects of age and breeding experience on female mating decisions. We used video techniques to examine female mate choice in guppies based on the area of carotenoid (orange) pigmentation on the body. Females were presented with paired images of males, one ornamented and the other plain. Visual preference for each male was measured. Age-related changes in the criteria of choice were examined by comparing the responses of the same mature but sexually inexperienced 6-mo-old and 12-mo-old females. Effects of breeding experience on female choice were examined by comparing mate preferences of 12-mo-old female virgins with their preferences after they had mated and produced a brood. Female preferences for ornamented males with large areas of carotenoid pigment changed with age but not with mating experience. Six-month-old virgin females preferred ornamented males, whereas 12-mo-old virgin and postpartum females did not differentiate between males based on orange coloration. The results are discussed in light of life-history theory and have important implications for studies of sexual selection as well as for the design of mate-choice studies.     

Sexual conflict over mating in Gnatocerus cornutus? Females prefer lovers not fighters

Female mate choice and male–male competition are the typical mechanisms of sexual selection. However, these two mechanisms do not always favour the same males. Furthermore, it has recently become clear that female choice can sometimes benefit males that reduce female fitness. So whether male–male competition and female choice favour the same or different males, and whether or not females benefit from mate choice, remain open questions. In the horned beetle, Gnatocerus cornutus, males have enlarged mandibles used to fight rivals, and larger mandibles provide a mating advantage when there is direct male–male competition for mates. However, it is not clear whether females prefer these highly competitive males. Here, we show that female choice targets male courtship rather than mandible size, and these two characters are not phenotypically or genetically correlated. Mating with attractive, highly courting males provided indirect benefits to females but only via the heritability of male attractiveness. However, mating with attractive males avoids the indirect costs to daughters that are generated by mating with competitive males. Our results suggest that male–male competition may constrain female mate choice, possibly reducing female fitness and generating sexual conflict over mating.     

No evidence of inbreeding avoidance in a polygynous ungulate: the reindeer (Rangifer tarandus)

In polygynous species, mate choice is an integrated part of sexual selection. However, whether mate choice occurs independently of the genetic relatedness among mating pairs has received little attention, although inbreeding may have fitness consequences. We studied whether genetic relatedness influenced females' choice of partner in a highly polygynous ungulate--the reindeer (Rangifer tarandus)--in an experimental herd during two consecutive rutting seasons; the herd consisting of 75 females in 1999 and 74 females in 2000 was exposed to three 4.5-year-old adults and three 1.5-year-old young males, respectively. The females' distribution during peak rut was not influenced by their genetic relatedness with the dominant males of the mating groups. Further, genetic relatedness did not influence the actual choice of mating partner. We conclude that inbreeding avoidance through mating group choice as well as choice of mating partner, two interconnected processes of female mate choice operating at two different scales in space and time, in such a highly female-biased reindeer populations with low level of inbreeding may not occur.