CRYPTIC FEMALE CHOICE: CRITERIA FOR ESTABLISHING FEMALE SPERM CHOICE

In this paper, I consider the criteria necessary to demonstrate the postcopulatory ability of females to favor the sperm of one conspecific male over another, that is, sperm choice. In practice it is difficult to distinguish between sperm competition and sperm choice, and sperm choice can be demonstrated only if the effects of sperm competition can be controlled. Few studies have used experimental protocols that do this, so evidence for sperm choice is limited. Moreover, in those studies in which sperm choice occurs, it does so to avoid incompatible genetic combinations and is therefore unlikely to result in directional sexual selection.     

FEMALE PREFERENCE FOR MALE COURTSHIP EFFORT CAN DRIVE THE EVOLUTION OF MALE MATE CHOICE

The evolution of male mate choice is constrained by costs of choice in species with a male‐biased operational sex ratio (OSR). Previous theoretical studies have shown that significant benefits of male choice are required, for example, by mating with more fecund females, in order for these costs to be offset and a male preference to spread. In a series of population genetic models we show the novel effect that male mating preference, expressed as a bias in courtship, can spread when females prefer, and thus are more likely to mate with, males who court more. We explore two female preference functions for levels of male courtship, one representing a threshold and the other a weighted female preference. The basic finding generally holds for both preference functions. However, the preference function greatly affects the spread of a male preference allele after the addition of competing males who can court more in total. Our results thus stress that a thorough understanding of the response of females to male courtship is a critical component to understanding male preference evolution in polygynous species.     

MALE MATE CHOICE AND THE EVOLUTION OF FEMALE PLUMAGE COLORATION IN THE HOUSE FINCH

The house finch (Carpodacus mexicanus) is a sexually dichromatic passerine in which males display colorful plumage and females are generally drab brown. Some females, however, have a subdued version of the same pattern of ornamental coloration seen in males. In previous research, I found that female house finches use male coloration as an important criterion when choosing mates and that the plumage brightness of males is a reliable indicator of male nest attentiveness. Male house finches invest substantially in the care of young and, like females, stand to gain by choosing high-quality mates. I therefore hypothesized that a female's plumage brightness might be correlated with her quality and be the basis for male mate choice. In laboratory mate choice experiments, male house finches showed a significant preference for the most brightly plumaged females presented. Observations of a wild population of house finches, however, suggest that female age is the primary criterion in male choice and that female plumage coloration is a secondary criterion. In addition, yearling females tended to have more brightly colored plumage than older females, and there was no relationship between female plumage coloration and overwinter survival, reproductive success, or condition. These observations fail to support the idea that female plumage coloration is an indicator of individual quality. Male mate choice for brightly plumaged females may have evolved as a correlated response to selection on females to choose brightly colored males.     

CRITERIA OF FEMALE MATE CHOICE IN DROSOPHILA LITTORALIS,D. MONTANA,AND D. EZOANA

We examined sexual selection by Drosophila littoralis, D. montana, and D. ezoana females on male courtship sounds to determine whether the females use absolute or relative criteria when choosing their mates. Behavior of the females was observed, when they were courted by a single male producing normal sounds, or by a single wing-manipulated male producing abnormal sounds; and when they were courted by one or both of these males in a choice situation. The females usually accepted short-winged (but not wingless) males producing abnormal sounds, if they had no alternatives. However, if they heard the sound produced by a normal male, they rejected the deficient male. Drosophila littoralis and D. ezoana females selected between two wing-manipulated males with different wing areas. Our results suggest that the females choose their mates on the basis of relative criteria if the signals emitted by the courting males are within the range of acceptable cues.     

MALE DOMINANCE, FEMALE MATE CHOICE, AND INTERSEXUAL CONFLICT IN THE ROSE BITTERLING (RHODEUS OCELLATUS)

An intersexual conflict arises when males and females differ in their reproductive interests. Although experimental studies have shown that females often mate with dominant males, it may not always be in the interest of a female to do so. Here we investigated the impact of male dominance on female mate choice and offspring growth and survival in the rose bitterling ( Rhodeus ocellatus ), a freshwater fish with a resource-based mating system. Three experimental mating trials were conducted using males of known dominance rank, but with different levels of constraint on male behavior. Thus, females were able to choose among; (1) males that were isolated from each other; (2) males that could see and smell each other, but could not directly interact; (3) males that could interact fully. Using a combination of behavioral observation and parentage analyses it was shown that female preferences did not correspond with male dominance and that male aggression and dominance constrained female mate choice, resulting in a potential intersexual conflict. The survival of offspring to independence was significantly correlated with female mate preferences, but not with male dominance. A lack of strong congruence in female preference for males suggested a role for parental haplotype compatibility in mate choice.     

EVOLUTION OF MATE CHOICE FOR GENOME-WIDE HETEROZYGOSITY

The extent to which indirect genetic benefits can drive the evolution of directional mating preferences for more ornamented mates, and the mechanisms that maintain such preferences without depleting genetic variance, remain key questions in evolutionary ecology. We used an individual-based genetic model to examine whether a directional preference for mates with higher genome-wide heterozygosity ( H ), and consequently greater ornamentation, could evolve and be maintained in the absence of direct fitness benefits of mate choice. We specifically considered finite populations of varying size and spatial genetic structure, in which parent–offspring resemblance in heterozygosity could provide an indirect benefit of mate choice. A directional preference for heterozygous mates evolved under broad conditions, even given a substantial direct cost of mate choice, low mutation rate, and stochastic variation in the link between individual heterozygosity and ornamentation. Furthermore, genetic variance was retained under directional sexual selection. Preference evolution was strongest in smaller populations, but weaker in populations with greater internal genetic structure in which restricted dispersal increased local inbreeding among offspring of neighboring females that all preferentially mated with the same male. These results suggest that directional preferences for heterozygous or outbred mates could evolve and be maintained in finite populations in the absence of direct fitness benefits, suggesting a novel resolution to the lek paradox.     

SEX DIFFERENCES IN MATE RECOGNITION AND CONSPECIFIC PREFERENCE IN SPECIES WITH MUTUAL MATE CHOICE

Sexual isolation is often assumed to arise because choosy females recognize and reject heterospecific males as mates. Yet in taxa in which both males and females are choosy, males might also recognize and reject heterospecific females. Here, we asked about the relative contribution of the sexes to the strong sexual isolation found in limnetic–benthic species pairs of threespine sticklebacks, which show mutual mate choice. We asked whether males and females of the two species recognize conspecifics and also prefer to mate with them. We found evidence for mate recognition by both sexes but only females prefer conspecifics. The nature of male courtship depended on which species of female they were courting, indicating that males recognized conspecific females and differentiated them from heterospecifics. However, males courted both species of females with equal vigor and changed courtship in a manner that would increase the chance of mating with heterospecifics. Females both recognized conspecifics and strongly preferred them. They responded very little to heterospecific male courtship and almost never mated with them. Therefore, males are likely to undermine sexual isolation, but females uphold it. Despite mutual mate choice and mate recognition in both sexes, females are primarily responsible for sexual isolation in these taxa.     

MUTUAL MATE CHOICE AND SEX DIFFERENCES IN CHOOSINESS

Sexual competition is associated closely with parental care because the sex providing less care has a higher potential rate of reproduction, and hence more to gain from competing for multiple mates. Sex differences in choosiness are not easily explained, however. The lower-caring sex (often males) has both higher costs of choice, because it is more difficult to find replacement mates, and higher direct benefits, because the sex providing more care (usually females) is likely to exhibit more variation in the quality of contributions to the young. Because both the costs and direct benefits of mate choice increase with increasing parental care by the opposite sex, general predictions about sex difference in choosiness are difficult. Furthermore, the level of choosiness of one sex will be influenced by the choosiness of the other. Here, we present an ESS model of mutual mate choice, which explicitly incorporates differences between males and females in life history traits that determine the costs and benefits of choice, and we illustrate our results with data from species with contrasting forms of parental care. The model demonstrates that sex differences in costs of choice are likely to have a much stronger effect on choosiness than are differences in quality variation, so that the less competitive sex will commonly be more choosy. However, when levels of male and female care are similar, differences in quality variation may lead to higher levels of both choice and competition in the same sex.     

GENETIC VARIATION FOR FEMALE MATE DISCRIMINATION IN DROSOPHILA MELANOGASTER

Comparisons between the Canton-S and Tai-Y strains of Drosophila melanogaster (both wild type) revealed variation in female mate discrimination based on chemical courtship signals present as hydrocarbons on the male cuticle. Mating tests indicated that 7-tricosene, which is the primary hydrocarbon on the Canton-S male cuticle but is nearly absent from Tai-Y, was a significant component of the signal. The discrimination was asymmetrical in that Canton-S females clearly distinguished between the two types of males in no-choice tests, but Tai-Y females did not. F₁ females expressed an intermediate ability to discriminate, and female progeny of backcrosses expressed a mating phenotype very similar to that of the parental strain to which the backcross was made. Analysis of independent effects from the X and both major autosomes indicated that the discrimination is controlled by gene(s) on chromosome 3.     

MATE CHOICE IN THE SAILFIN MOLLY,POECILIA LATIPINNA

We examined both female and male mate choice in the sailfín molly, Poecilia latipinna. Female mollies preferred larger males over smaller ones when comparing males from their own populations. Although the expression of this preference depends on a female's receptive state, the level of female preference does not appear to be associated with any other attribute of the female or of the males. When presented with males of the same size from different populations, females preferred native over foreign males in some but not all population combinations. These results cannot be explained by a bias for higher size-specific rates of courtship displays that is shared by all females. Males preferred larger over smaller females; larger males exhibited stronger preferences, and preference for the larger female also increased as the disparity in size between the two object females increased. We found no evidence that males preferred native over foreign females when encountered singly or in size-matched combinations. These results indicate that discrimination among populations arises because females exercise divergent directional preferences for size-specific trait values that are associated with differences among males in these values. This result implies an active role for sexual selection in contributing to the maintenance of the behavioral or morphological distinctions among males observed within and among populations.     

熟悉性对棕色田鼠和根田鼠择偶行为的影响

以两性配对共居至交配或生仔作不同熟悉处理,在Y字型选择箱中分别观察棕色田鼠,根田鼠的择偶行为和配偶识别。结果如下：（1）棕色田鼠雌雄两性均表现出对熟悉异性或配偶的喜好倾向;（2）在根 中,只有雌性表现出对熟悉雄鼠或配偶的选择倾向,雄鼠无明显的选择取向;（3）每种雌性田鼠对2种熟悉性不同的同种雄性的嗅舔时间均有显著差异性,而每种雄性田鼠对2种熟悉性不同的同种雌性的嗅舔时间均无显著差异性。这些结果表明：（1）熟悉性对棕色田鼠择偶行为的影响大于对根田鼠的影响;（2）嗅舔时间差别可反映不同田鼠的配偶识别能力,熟悉性对棕色田鼠配偶识别能力的影响大于对根田鼠的影响;（3）2种田鼠配偶识别的性别差异的一致性,提示这2种田鼠的雌性配偶识别能力均强于雄性田鼠,而雌鼠的配偶识别能力可能取决于雌鼠受酱或分娩刺激的生理状态;（4）棕色田鼠室内所表现的择偶行为的两性熟悉性特征与其单配制有关,根田鼠所表现的择偶行为的雌性熟悉性特征与其一雄多雌制有关。     

ASSORTATIVE MATE CHOICE AND DOMINANCE MODIFICATION: ALTERNATIVE WAYS OF REMOVING HETEROZYGOTE DISADVANTAGE

In genetic polymorphisms of two alleles, heterozygous individuals may contribute to the next generation on average more or fewer descendants than the homozygotes. Two different evolutionary responses that remove a disadvantageous heterozygote phenotype from the population are the evolution of strictly assortative mate choice, and that of a modifier making one of the two alleles completely dominant. We derive invasion fitness of mutants introducing dominance or assortative mate choice in a randomly mating population with a genetic polymorphism for an ecological trait. Mutations with small effects as well as mutants introducing complete dominance or perfect assorting are considered. Using adaptive dynamics techniques, we are able to calculate the ratio of fitness gradients for the effects of a dominance modifier and a mate choice locus, near evolutionary branching points. With equal resident allele frequencies, selection for mate choice is always stronger. Dominance is more strongly selected than assortative mating when the resident (common) alleles have very unequal frequencies at equilibrium. With female mate choice the difference in frequencies where dominance is more strongly selected is smaller than when mutants of both sexes can choose without costs. A symmetric resource-competition model illustrates the results.     

MECHANISMS OF FEMALE CHOICE IN RED JUNGLE FOWL

We examined mate preference behavior in red jungle fowl, Gallus gallus, to determine if the mechanism of mate preference used by females was relative or absolute. Under a relative model, females compare males and prefer the one with the most exaggerated form of secondary sex character, regardless of where the proffered males lie along the population distribution of the trait. Under an absolute or threshold model, females have a threshold for the character, above which they will exert a preference and below which they will not. Female red jungle fowl preferred roosters with longer combs and redder irises, but this preference was exerted only when hens mated quickly; females mating slowly mated at random. The threshold model was supported in two ways: i) chosen males from the fast-mating group had larger combs than chosen males in the slow-mating group; ii) when the same female was presented with two pairs of males in two different trials, one large-combed pair and one small-combed pair, hens mated significantly more slowly, and often refused to mate, when only short-combed roosters were available. Hens thus alter their behavior depending on the males they see, and they may not exert a preference at all if both males fall below the threshold. Further corroborating evidence comes from a set of mate choice trials using underdeveloped roosters, in which males had small combs and females mated slowly or did not mate. The method of choice used by females could affect the speed with which correlations develop between the genes for male traits and genes for female preferences. Sexual selection for good genes may be more consistent with an absolute than a relative method of female choice.