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.     

Evidence of an emerging female preference for an artificial male trait and the potential for spread via mate choice copying in Poecilia latipinna

The initial purpose of the project described herein was to assess the preference of female Poecilia latipinna for an artificial novel male trait—an orange‐colored distal fringe added to the caudal fin of an otherwise wild‐type conspecific. Analysis of the preliminary data revealed consistent individual differences in the strength of female preference for either orange‐tailed or wild‐type males. This finding inspired the study's second aim—to evaluate whether the preference for orange‐tailed males observed among a subset of females could spread via mate choice copying to others in the population that initially preferred wild‐type males. Two experiments and a control were conducted wherein females were simultaneously presented with an orange‐tailed and a wild‐type dummy male using a standard dichotomous choice design. In the first experiment, female preference was assessed on two separate occasions in order to characterize the variability and consistency in preference for orange‐tailed versus wild‐type males. The second experiment addressed mate choice copying: Female preference was again assessed on two separate occasions, but involved pairing a model female with the non‐preferred male for a period of time between preference tests. A third set of control tests were conducted using the same protocol as the copying experiment except that subject females were unable to see the model paired with the non‐preferred male. Results showed that, although females collectively preferred neither the orange‐tailed nor the wild‐type dummy male in the first round of preference tests, the majority showed relatively strong individual preferences. The subset of females that preferred the orange‐tailed over the wild‐type male in the first round of testing all maintained their preferences in the second round whether or not they had observed a model in association with the non‐preferred wild‐type male between tests. However, females that preferred the wild type over the orange male in the first round of testing copied the model's choice of the non‐preferred orange‐tailed male in their second round of preference testing. These results highlight the importance of recognizing the likelihood that only a subset of females will express a preference as it first emerges within a population. In such instances, the preference may not be detected at the population level—a point frequently overlooked in studies of mate choice. Additionally, these data highlight the importance of assessing the preferences of individual females and their capacity to drive evolutionary change within populations. Lastly, this study offers evidence of a possible mechanism by which a novel male trait might spread via mate choice copying by exploiting an emerging sensory bias within a subset of females in the population.     

Female Attraction to Higher Pitched Male Enticement Calls in Barn Swallows

Current sexual selection studies demonstrate that female mate preference almost always favors exaggerated male traits, such as colorful plumage and elongated tails. However, such studies focused mainly on secondary sexual characteristics, i.e., traits that are fully developed at maturation, while ignoring others, which precludes generalization of the findings. We studied the expression of the male enticement call, a nestling‐like courtship trait, in relation to female attraction and to the expression of secondary sexual ornaments in the Japanese barn swallow Hirundo rustica gutturalis. First, we showed that the peak amplitude frequency of male enticement calls was, on average, lower than that of nestling food‐begging calls, indicating that higher pitched calls are more similar to nestling food‐begging calls than are lower pitched calls. Second, we conducted an experimental playback of male enticement calls during the courtship period with the female's mate removed, and found that females were more attracted to heightened‐pitch calls than to control calls. Lastly, the peak amplitude frequency of male enticement calls was negatively related to the ornamentation, as measured by throat coloration. Taken together, these findings suggest the following: (1) females are attracted to a more nestling‐like trait, and (2) similarity to nestling food‐begging calls increases with decreasing secondary sexual ornaments. Nestling‐like male traits that are not secondary sexual characteristics should be considered when studying the general pattern of female attraction to male traits.     

Female Preferences for Male Song Characters in the Bush-Cricket Isophya camptoxypha (Orthoptera, Tettigonioidea)

Female preferences for two male song characters (duration of syllables [DS], syllable repetition period [SRP]) have been studied in Isophya camptoxypha, an Eastern European duetting bush-cricket. Songs with modified DS or SRP were presented to virgin females and their response songs were recorded and counted. Female preference functions were unimodal for both characters. But while in the case of SRP the obtained female preference function reached its maximum at the mean value of that character, in the case of DS females preferred modified songs with a DS slightly higher than the natural range of that character. A comparison between the obtained preference functions and the DS and SRP values measured in sympatric Isophya species (with similar song structure) suggests that the two examined characters and female preferences for them may be effective components of the species-specific mate recognition system of I. camptoxypha. Moreover DS values may also convey information about the quality of the singing male.     

The evolution of preference strength under sensory bias: a role for indirect selection?

Evidence suggests that female preferences may sometimes arise through sensory bias, and that males may subsequently evolve traits that increase their conspicuousness to females. Here, we ask whether indirect selection, arising through genetic associations (linkage disequilibrium) during the sexual selection that sensory bias imposes, can itself influence the evolution of preference strength. Specifically, we use population genetic models to consider whether or not modifiers of preference strength can spread under different ecological conditions when female mate choice is driven by sensory bias. We focus on male traits that make a male more conspicuous in certain habitats-and thus both more visible to predators and more attractive to females-and examine modifiers of the strength of preference for conspicuous males. We first solve for the rate of spread of a modifier that strengthens preference within an environmentally uniform population; we illustrate that this spread will be extremely slow. Second, we used a series of simulations to consider the role of habitat structure and movement on the evolution of a modifier of preference strength, using male color polymorphisms as a case study. We find that in most cases, indirect selection does not allow the evolution of stronger or weaker preferences for sensory bias. Only in a "two-island" model, where there is restricted migration between different patches that favor different male phenotypes, did we find that preference strength could evolve. The role of indirect selection in the evolution of sensory bias is of particular interest because of ongoing speculation regarding the role of sensory bias in the evolution of reproductive isolation.     

Interaction Between Sexually Antagonistic Selection and Mate Choice in the Evolution of Female Responses to Male Traits

Theoretical analyses of selection on mutations affecting female responsiveness to male traits suggested that sexually antagonistic selection and traditional female choice are not exclusive alternatives. They can act simultaneously on the same female traits, and can either reinforce or act against each other. These analyses do not yield theoretical predictions regarding the relative frequency and importance of the two types of selection on female responsiveness, as the balance between them is affected by complex factors, including the frequency distribution of male traits, and the mechanisms of male action. Male–female interactions differ from many other evolutionary interactions involving potential evolutionary conflict, in that male and female genomes are irretrievably mixed in their offspring, thus increasing the possibility of indirect payoffs to one participant from the traits of its partner.     

Poecilia picta,a Close Relative to the Guppy,Exhibits Red Male Coloration Polymorphism: A System for Phylogenetic Comparisons

Studies on the evolution of female preference and male color polymorphism frequently focus on single species since traits and preferences are thought to co-evolve. The guppy, Poecilia reticulata, has long been a premier model for such studies because female preferences and orange coloration are well known to covary, especially in upstream/downstream pairs of populations. However, focused single species studies lack the explanatory power of the comparative method, which requires detailed knowledge of multiple species with known evolutionary relationships. Here we describe a red color polymorphism in Poecilia picta, a close relative to guppies. We show that this polymorphism is restricted to males and is maintained in natural populations of mainland South America. Using tests of female preference we show female P. picta are not more attracted to red males, despite preferences for red/orange in closely related species, such as P. reticulata and P. parae. Male color patterns in these closely related species are different from P. picta in that they occur in discrete patches and are frequently Y chromosome-linked. P. reticulata have an almost infinite number of male patterns, while P. parae males occur in discrete morphs. We show the red male polymorphism in P. picta extends continuously throughout the body and is not a Y-linked trait despite the theoretical prediction that sexually-selected characters should often be linked to the heterogametic sex chromosome. The presence/absence of red male coloration of P. picta described here makes this an ideal system for phylogenetic comparisons that could reveal the evolutionary forces maintaining mate choice and color polymorphisms in this speciose group.     

Male Mating History Influences Female Mate Choice in the Trinidadian Guppy (Poecilia reticulata)

Based on the phenotype‐linked fertility hypothesis, sexual selection should favour females that can accurately assess the recent mating history of available sexual partners and preferentially avoid mating with recently‐mated males [who may be sperm depleted (SD)] so as to minimize the risk of their eggs not being fertilized. This hypothesis has received to date only limited attention and empirical support. Therefore, in the current study, we investigated experimentally whether females of a vertebrate species, the Trinidadian guppy (Poecilia reticulata), are able to assess the recent mating history of males, and thus potentially their functional fertility, and choose to avoid mating with males that appear to have recently mated and who may be sperm limited. Individual virgin females were first given a dichotomous choice between a male that had not been recently observed to interact sexually with another female (i.e. not sperm‐depleted) and another male that had been observed to interact sexually with a female (i.e. potentially sperm‐depleted) as sexual partners. Paired males were matched for body length and coloration. Immediately following this test, the focal females were subjected to a free‐swimming mate‐choice test using the same paired stimulus males. As predicted, on average, female guppies avoided the apparently recently‐mated (and potentially sperm‐depleted) male and exhibited a significant preference for the other male not recently observed mating (and thus not likely sperm limited) during both tests. We do not yet fully understand the underlying mechanisms of this preference. Therefore, further research on the particular cues that females use to assess the recent mating history and fertility status of males is required.     

Female choice linked to male dorsal fin height in a shortfin molly

Sexual selection is a possible mechanism of speciation. This could be true even in systems where female mate choice has not been clearly observed, because pre-existing biases may be expressed if female decision-making results in male trait evolution. In some mollies, males have enlarged dorsal fins and courtship display is the prevailing mating process. In others, male dominance is thought to play a greater role. We tested females of a species in the latter group, Poecilia mexicana, for consistent preference related to dorsal fin morphology. We found that females were biased toward larger dorsal fins. This latent preference could be an important driver in trait evolution.     

雌性偏好促进象型类的性别异时进化（英文）

性双型的特征通常被认为产生于种内争夺交配优先权的斗争。例如,现生和化石的雄性长鼻类动物具有较大的体型和较粗壮的上门齿。本研究阐释了如下现象:化石象型类动物(Elephantiformes,长鼻类的主要类群)一些性双型特征与其进化历史具有相关性,而与性别竞争并非直接相关。在中新世的葛氏铲齿象(Platybelodon grangeri)和狭齿嵌齿象(Gomphotherium angustidens)中,雄性比雌性倾向于具有进化中更进步的特征,如同雄性在进化中领先雌性一步。这种现象可能与雌性偏好的机制相耦合。在象型类动物进化的早期(繁荣期),性别选择压促使雄性比雌性产生更加显著的进步特征;然而,在它们进化的晚期(衰退期),性别选择压似乎减弱,性别的异时进化也减少。这种新的发现或许在大型有蹄类的演化过程中有一定的普遍意义,因为那些繁荣的类群中通常性双型显著,如鹿科和牛科;而衰落的类群中通常性双型不显著。     

Male receiver bias for red agonistic signalling in a yellow-signalling widowbird: a field experiment

Receiver bias models of signal evolution are typically regarded as alternatives or complements to ornament evolution due to coevolving mate choice, whereas sexually or socially selected agonistic signals are rarely studied with respect to receiver psychology. Against the background of convergent evolution of red agonistic signals from yellow ancestors in the genus Euplectes (widowbirds and bishops), we experimentally test the function of a yellow signal in the montane marsh widowbird (E. psammocromius), as well as a hypothesized receiver bias for redder (longer wavelength) hues. In a field experiment in southern Tanzania, males that had their yellow wing patches blackened lost their territories or lost territorial contests more often than controls or reddened males, which together with a longer wavelength hue in territory holders, indicates an agonistic signal function. Males painted a novel red hue, matching that of red-signalling congeners, retained their territories and won contests more often than controls. To our knowledge, this is the first demonstration of a receiver bias driving agonistic signal evolution. Although the sensory or cognitive origin of this bias is yet unknown, it strengthens our view that genetically constrained signal production (i.e. carotenoid metabolism), rather than differential selection, explains the carotenoid colour diversification in Euplectes.     

Female age: Male preference and reproductive success in primates

A survey of the literature on male sexual preferences according to the age of the female partner supported the hypothesis that adult males should prefer older females of higher parity. Reproductive success was also surveyed by age and parity, and younger females of lower parity were universally found to have lower success than older females of higher parity. This appears to be true for either age or parity independently, as well as in combination. These findings are discussed and applied to human societies, where similar trends would be expected.     

GENETIC CORRELATION BETWEEN A FEMALE MATING PREFERENCE AND THE PREFERRED MALE CHARACTER IN SEAWEED FLIES (COELOPA FRIGIDA)

The mating preferences of female seaweed flies Coelopa frigida were determined by observing their acceptance or rejection of males of known size. The inversion karyotype of both males and females was also determined. Females exhibited a preference to mate with large males, and evidence is presented that a genetic correlation exists between the female preference and the preferred trait. Females carrying the inversion karyotype associated with large male size showed a strong preference for large males; females carrying the inversion associated with small male size also exhibited a preference for large males, but it was significantly less strong. This finding suggests that a Fisherian process may be operating.     

Male Sexual Signals and Female Choice in Drosophila grimshawi (Diptera: Drosophilidae)

Sexual selection and sexual signaling have been prominent topics in recent behavioral studies, but limited data have led to controversy regarding these topics. For example, the Hawaiian Drosophila are often cited as examples in which female choice has resulted in the evolution of elaborate male courtship signals, but relatively few data exist to test these claims adequately. We studied D. grimshawi, a lek-forming Hawaiian Drosophila, to determine whether there was evidence for female choice without male competition and to elucidate the possible cues females use to discriminate. Male mating success was found to be nonrandom and males that courted females intensely and deposited many pheromone-containing streaks on the substrate were the most successful. Hence, multiple cues seem to be involved in male mating success in this species. Some males performed only one display, however, and may represent an alternate male mating tactic. The protein content of the adult male diet significantly influenced the level of pheromone streak deposition, and thus, foraging environment may affect the outcome of sexual selection.     

Female preference for multi-modal courtship: multiple signals are important for male mating success in peacock spiders

A long-standing goal for biologists has been to understand how female preferences operate in systems where males have evolved numerous sexually selected traits. Jumping spiders of the Maratus genus are exceptionally sexually dimorphic in appearance and signalling behaviour. Presumably, strong sexual selection by females has played an important role in the evolution of complex signals displayed by males of this group; however, this has not yet been demonstrated. In fact, despite apparent widespread examples of sexual selection in nature, empirical evidence is relatively sparse, especially for species employing multiple modalities for intersexual communication. In order to elucidate whether female preference can explain the evolution of multi-modal signalling traits, we ran a series of mating trials using Maratus volans. We used video recordings and laser vibrometry to characterize, quantify and examine which male courtship traits predict various metrics of mating success. We found evidence for strong sexual selection on males in this system, with success contingent upon a combination of visual and vibratory displays. Additionally, independently produced, yet correlated suites of multi-modal male signals are linked to other aspects of female peacock spider behaviour. Lastly, our data provide some support for both the redundant signal and multiple messages hypotheses for the evolution of multi-modal signalling.     

Countergradient variation in the sexual coloration of guppies (Poecilia reticulata): drosopterin synthesis balances carotenoid availability

Trinidad guppies (Poecilia reticulata) are distributed along an environmental gradient in carotenoid availability that limits the carotenoid content of the orange spots of males. The amount of synthetic red pteridines (drosopterins) in the orange spots covaries with the carotenoid content, such that the ratio of the two types of pigments is roughly conserved across streams. Carotenoids and drosopterins have different spectral properties and thus the ratio of the two types of pigments affects the shape of the orange spot reflectance spectrum. Geographic conservation of the carotenoid:drosopterin ratio suggests that males may be under selection to maintain a particular hue. We tested this hypothesis by comparing the pigmentation and coloration of guppies from six streams in the field to that of second-generation descendants of the same populations raised on three dietary carotenoid levels in the laboratory. The results show clearly that the geographic variation in drosopterin production is largely genetic and that the hue of the orange spots is conserved among populations in the field, relative to the laboratory diet groups. This is a countergradient pattern because genetic differences between populations in drosopterin production mask the effect of carotenoid availability on the hue of the orange spots. The potential for countergradient sexual selection to contribute to reproductive isolation between populations is discussed.