Mating effort and female receptivity: how do male guppies decide when to invest in sex?

Sub-acute exposure of male guppies (Poecilia reticulata) to environmentally relevant concentrations of PFOA and GenX induces significant changes in the testis transcriptome and reproductive traits

Poly- and perfluoroalkyl substances (PFAS) are frequently detected in the environment and are linked to adverse reproductive health outcomes in humans. Although legacy PFAS have been phased out due to their toxicity, alternative PFAS are increasingly used despite the fact that information on their toxic effects on reproductive traits is particularly scarce. Here, we exposed male guppies (Poecilia reticulata) for a short period (21 days) to an environmentally realistic concentration (1 ppb) of PFOA, a legacy PFAS, and its replacement compound, GenX, to assess their impact on reproductive traits and gene expression. Exposure to PFAS did not impair survival but instead caused sublethal effects. Overall, PFAS exposure caused changes in male sexual behaviour and had detrimental effects on sperm motility. Sublethal variations were also seen at the transcriptional level, with the modulation of genes involved in immune regulation, spermatogenesis, and oxidative stress. We also observed bioaccumulation of PFAS, which was higher for PFOA than for GenX. Our results offer a comprehensive comparison of these two PFAS and shed light on the toxicity of a newly emerging alternative to legacy PFAS. It is therefore evident that even at low concentrations and with short exposure, PFAS can have subtle yet significant effects on behaviour, fertility, and immunity. These findings underscore the potential ramifications of pollution under natural conditions and their impact on fish populations.

Black and orange coloration predict success during male–male competition in the guppy

Investigating how intrasexual competition and intersexual mate choice act within a system is crucial to understanding the maintenance and diversity of sexually-dimorphic traits. These two processes can act in concert by selecting for the same trait, or in opposition by selecting for different extremes of the same trait; they can also act on different traits, potentially increasing trait complexity. We asked whether male–male competition and female mate choice act on the same male traits using Trinidadian guppies, which exhibit sexual size dimorphism and male-limited color patterns consisting of different colors arranged along the body and fins. We used behavioral assays to assess the relationship between color and competitive success and then compared our results to the plethora of data on female choice and color in our study population. Males initiated more contests if they were larger than their competitor. Males won contests more often if they had more black coloration than their competitor, and the effect of black was stronger when males had less orange than their competitor. Additionally, males won more often if they had either more structural color (iridescence) and more orange, or less structural color and less orange than their competitor, suggesting multiple combinations of color traits predict success. Females from our study population exhibit a strong preference for more orange coloration. Thus, traits favored in male contests differ from those favored by intersexual selection in this population. These results suggest that inter- and intrasexual selection, when acting concurrently, can promote increased complexity of sexually selected traits.

Visual Background Choice and Light Environment Affect Male Guppy Visual Contrast

Male guppies (Poecilia reticulata) have multiple colored spots and perform courtship displays near the edges of streams in Trinidad in shallow water flowing through rainforest. Depending upon the orientation of the pair, the female sees the male displays against gravel or other stream bed substrates or against the spacelight—the roughly uniform light coming from the water column away from the bank. We observed courting pairs in two adjacent natural streams and noted the directions of each male display. We found that the female sees the male more often against spacelight than against gravel when females either faced the spacelight from the opposite bank or from downstream, or both. Visual modelling using natural substrate reflectances and field light measurements showed higher chromatic contrast of males against spacelight than against substrates independent of the two ambient light environments used during displays, but achromatic contrast depended upon the ambient light habitat. This suggests that courtship involves both chromatic and achromatic contrast. We conclude that the orientation of courting pairs and the ambient light spectrum should be accounted for in studies of mate choice, because the visual background and light affect visibility, and these differ with orientation.

Male mate choice in mosquitofish: personality outweighs body size

Background

Despite its important implications in behavioural and evolutionary ecology, male mate choice has been poorly studied, and the relative contribution of personality and morphological traits remains largely unknown. We used standard two-choice mating trials to explore whether two personality traits (i.e., shyness and activity) and/or body size of both sexes affect mate choice in male mosquitofish Gambusia affinis. In the first set of trials involving 40 males, we tested whether males would prefer larger females and whether the preference would be affected by males’ body length and personality traits, and females’ activity level. In the second set of trials (using another 40 males), we tested whether males would prefer more active females and whether the preference would be affected by males’ body length and personality traits.

Results

Both shyness and activity in males were significantly repeatable and constituted a behavioural syndrome. No overall directional preference for large (or small) females with the same activity levels was detected because larger males preferred larger females and smaller males chose smaller females. Males’ strength of preference for larger females was also positively correlated with the activity level of larger females but negatively with the activity level of smaller females. Males spent more time associating with active females regardless of their body lengths, indicating males’ selection was more influenced by female activity level than body size. Males’ preference for inactive females was enhanced when females became active. There was no convincing evidence for the effect of males’ personality traits or body length on their preferences for females’ activity level.

Conclusions

Our study supports the importance of body size in male mate choice but highlights that personality traits may outweigh body size preferences when males choose mating partners.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12983-022-00450-3.

Alternative reproductive tactics in male freshwater fish influence the accuracy of species recognition

Sexual conflict can result in coercive mating. Because males bear low costs of heterospecific mating, coercive males may engage in misdirected mating attempts toward heterospecific females. In contrast, sexual selection through consensual mate choice can cause mate recognition cues among species to diverge, leading to more accurate species recognition. Some species show both coercive mating and mate choice-associated courtship behaviors as male alternative reproductive tactics. We hypothesized that if the selection pressures on each tactic differ, then the accuracy of species recognition would also change depending on the mating tactic adopted. We tested this hypothesis in the guppy (Poecilia reticulata) and mosquitofish (Gambusia affinis) by a series of choice experiments. Poecilia reticulata and G. affinis males both showed imperfect species recognition and directed all components of mating behavior toward heterospecific females. They tended to direct courtship displays more frequently toward conspecific than heterospecific females. With male P. reticulata, however, accurate species recognition disappeared when they attempted coercive copulation: they directed coercions more frequently toward heterospecific females. We also found that heterospecific sexual interaction had little effect on the fecundity of gravid females, which suggests that prepregnancy interactions likely underpin the exclusion of G. affinis by P. reticulata in our region.

Courtship behaviour influences social partner choice in male guppies

Although male courtship displays have evolved primarily to sexually attract females, they also generate inadvertent public information that potentially reveals the courter’s relative sexual attractiveness and the perceived quality and sexual receptivity of the female being courted to nearby eavesdropping male competitors, who in turn may use this information to bias their social partner choices. We tested this hypothesis by first presenting individual eavesdropping male guppies (Poecilia reticulata) the opportunity to simultaneously observe two demonstrator males whose courtship behaviour was manipulated experimentally to differ, following which we tested them for their preference to associate socially with either demonstrator males. Test males preferentially associated with the demonstrator male who they had previously observed courting a female over the other (non-courting) demonstrator. This social association preference was not expressed in the absence of a female to court. Our findings highlight the potential for sexual behaviour influencing male-male social associations in nature.

Exploring the threat-sensitive predator avoidance hypothesis on mate competition in two wild populations of Trinidadian guppies

The intensity of mate competition is often influenced by predation pressure. The threat-sensitive predator avoidance hypothesis predicts that prey should precisely adjust their fitness-related activities to the level of perceived acute predation risk and this effect should be stronger under high background risk. Individuals should compensate during periods of moderate risk for lost opportunities during high risk. Our study examined the interaction between acute and background predation risk on mate competition. Under laboratory conditions, we explored the effects of acute risk (low vs. high) using chemical alarm cue (AC; control (results presented in Chuard et al. (2016)) The effects of adult sex ratio on mating competition in male and female guppies (Poecilia reticulata) in two wild populations. Behav Process 129:1-10), 25 % concentration, and 100 % concentration), and population of origin (low vs. high background risk) on mate competition in guppies (Poecilia reticulata). Surprisingly, males favored courtship over forced mating under acute predation risk irrespective of background risk, potentially benefiting from a female preference for bold males. We discuss our results in the context of chemical threat-sensitivity and resource differences in defendability (e.g. mates vs. food).

Male mate choice in livebearing fishes: an overview

Although the majority of studies on mate choice focus on female mate choice, there is growing recognition of the role of male mate choice too. Male mate choice is tightly linked to 2 other phenomena: female competition for males and ornamentation in females. In the current article, I review the existing literature on this in a group of fishes, Poeciliidae. In this group, male mate choice appears to be based on differences in female quality, especially female size, which is a proxy for fecundity. Some males also have to choose between heterospecific and conspecific females in the unusual mating system of the Amazon molly. In this case, they typically show a preference for conspecific females. Whereas male mate choice is relatively well documented for this family, female ornamentation and female competition are not.

Male courtship decisions are influenced by light environment and female receptivity

The appearance of animal colour signals depends jointly upon the ambient light spectrum and the signal's reflectance spectra. Light environment heterogeneity might, therefore, allow individuals to enhance their signal by signalling in an environment that increases signal efficacy. We tested this hypothesis by providing male guppies (Poecilia reticulata), a choice of three light environments in which to display their colour signal to females: green, lilac, and clear. We paired males with both receptive and non-receptive females to test whether female response might affect male behavioural decisions. Males preferred the clear environment in all trials and this environment also resulted in males having the highest average visual contrast. Sexual behaviour was influenced by complex interactions between female receptivity, light environment, and male colour pattern contrast. Males spent significantly more time in the environment in which their colour signal had the highest contrast, but only when paired with receptive females. Significant interactions between light environment and individual male colour components were also seen only in receptive trials. Our results suggest that males use light environment to enhance their colour pattern, but only in the presence of receptive females.

The effects of perceived mating opportunities on patterns of reproductive investment by male guppies

Males pay considerable reproductive costs in acquiring mates (precopulatory sexual selection) and in producing ejaculates that are effective at fertilising eggs in the presence of competing ejaculates (postcopulatory sexual selection). Given these costs, males must balance their reproductive investment in a given mating to optimise their future reproductive potential. Males are therefore expected to invest in reproduction prudently according to the likelihood of obtaining future matings. In this study we tested this prediction by determining whether male reproductive investment varies with expected future mating opportunities, which were experimentally manipulated by visually exposing male guppies (Poecilia reticulata) to high or low numbers of females in the absence of competing males. Our experiment did not reveal consistent effects of perceived future mating opportunity on either precopulatory (male mate choice and mating behaviour) or postcopulatory (sperm quality and quantity) investment. However, we did find that male size and female availability interacted to influence mating behaviour; large males visually deprived of females during the treatment phase became more choosy and showed greater interest in their preferred female than those given continuous visual access to females. Overall, our results suggest males tailor pre- rather than postcopulatory traits according to local female availability, but critically, these effects depend on male size.

Covariation and repeatability of male mating effort and mating preferences in a promiscuous fish

Although mate choice by males does occur in nature, our understanding of its importance in driving evolutionary change remains limited compared with that for female mate choice. Recent theoretical models have shown that the evolution of male mate choice is more likely when individual variation in male mating effort and mating preferences exist and positively covary within populations. However, relatively little is known about the nature of such variation and its maintenance within natural populations. Here, using the Trinidadian guppy (Poecilia reticulata) as a model study system, we report that mating effort and mating preferences in males, based on female body length (a strong correlate of fecundity), positively covary and are significantly variable among subjects. Individual males are thus consistent, but not unanimous, in their mate choice. Both individual mating effort (including courtship effort) and mating preference were significantly repeatable. These novel findings support the assumptions and predictions of recent evolutionary models of male mate choice, and are consistent with the presence of additive genetic variation for male mate choice based on female size in our study population and thus with the opportunity for selection and further evolution of large female body size through male mate choice.

Do unattractive friends make you look better? Context-dependent male mating preferences in the guppy

Recent theory predicts that in species where females tend to mate with the relatively most ornamented males, males may increase their attractiveness to females, and hence mating success, by preferentially associating with females that are surrounded by less ornamented competitors. Despite this prediction, we still lack explicit experimental evidence that males strategically prefer females surrounded by less attractive competitors to maximize their relative attractiveness. In this paper, we provide a comprehensive test of this hypothesis in the guppy (Poecilia reticulata), a species where a female's perception of a male's attractiveness depends on his coloration relative to that of surrounding males. We found that males preferentially associated with females that were surrounded by relatively drab competitors, and that the strength of an individual male's preference was negatively correlated with his level of ornamentation. A series of control experiments made it possible to exclude the potentially confounding effects of male-male competition or social motivations when drawing these conclusions. The ability of males to choose social context to increase their relative attractiveness has important evolutionary consequences, for example, by contributing towards the maintenance of variability in male sexual ornamentation despite the strong directional selection exerted by female preferences.

Recent social history alters male courtship preferences

Phenotypically plastic mating behavior may allow males to modify their reproductive behavior to suit the prevailing social conditions, but we do not know if males only react to immediate social stimuli or change their inherent mate preferences according to their social history. Here we examine the effect of social experiences on the subsequent reproductive behavior of male guppies under standard conditions, allowing us to distinguish the effect of past and immediate social conditions. Males experienced experimental conditioning periods during which they interacted with three females, either of variable size or of similar size. Females arrived either simultaneously or consecutively. In subsequent standard assays, only males that had experienced females of variable size preferentially courted large females. Further, males exposed to sequential female arrival courted subsequent females more vigorously than males that had experienced simultaneous female arrival. In contrast, males did not alter their coercive mating attempts in relation to their recent social history. These results demonstrate that males use past experiences to modify their subsequent reproductive behavior rather than reacting only to immediate stimuli, and reveal the sophisticated ways in which males alter their reproductive tactics to suit the social environment and maximize fitness across changing selective landscapes.