Sperm competition risk and mate choice in male Trinidadian guppies, Poecilia reticulata

Mate Discrimination Using Chemical Cues by Male Guppies

Males often perform mate choice with the aim of maximizing reproductive success. To identify profitable mates, the males of some animals are known to use visual and chemical cues derived from females. In this study, we aimed to examine mate discrimination by male guppies (Poecilia reticulata) using chemical cues received from females under different reproductive statuses, i.e., virgin females, pregnant females, females after copulation with another male, and post-partum females. We conducted a dichotomous choice experiment for each combination of chemical stimuli from females under different reproductive statuses. In experiment 1, in which females were removed from water that was subsequently used as a chemical stimulus, male preferences did not differ significantly in all combinations of chemical stimuli from females under different reproductive statuses. However, in experiment 2, in which females remained within bottles containing the water used as a chemical stimulus, with the exception of one combination of chemical stimuli, significant differences in male preferences were detected for chemical stimuli derived from females under different reproductive statuses. Overall, males generally showed a preference for chemical stimulus received from females after copulation with other males. The findings of this study indicate that male guppies can discriminate the reproductive status of females based solely on chemical cues that may disappear or degenerate within a short period of time, thereby facilitating profitable mate choice.

The Effects of a Male Audience on Male and Female Mating Behaviour in the Blood-Sucking Bug Rhodnius prolixus

Social context is a key factor affecting sexual behaviour and cannot be neglected in gregarious species, such as triatomine blood-sucking bugs. Here we study the influence of the social context on the sexual reproductive behaviour of males and females of Rhodnius prolixus Stål. Specifically, we identify and compare the frequencies and sequence of sexual behaviours exhibited by a focal pair in presence or absence of a male audience. We expect that in presence of a male audience females increase their selectiveness level since the risk of losing infertile eggs decreases in presence of more candidates and females can benefit from copulating with a better quality male. Besides, in presence of potential rivals, we expect changes in the sexual behaviour of focal males, associated to a reduction in the risk of sperm competition. As expected, in presence of a male audience, females significantly increased the exhibition of rejection behaviour. Moreover, focal males exhibited shorter latencies to mount the female, longer duration of copula, and differences in their stereotyped behaviour exhibited during copula. We discuss the influence of the social context on the reproductive behaviour of females and males of R. prolixus.

Males can't afford to be choosy: Male reproductive investment does not influence preference for female size in Limia (Poeciliidae)

Reproductive investment was initially thought to be the key selective force behind male mate preference for female characters, like size or ornamentation (i.e., the preference by males for certain females). Yet, evidence of polygynous species, where male reproductive investments are often inexpensive compared to those of females, have also been described to possess male preference. Our study aims to understand how reproductive investment influences the selection of choosy males in polygynous systems using two species of livebearing fishes varying in reproductive investment: Limia perugiae, in which males invest heavily into reproduction, and L. zonata in which males invest minimally into reproduction. We hypothesized that male reproductive investment when combined with fecundity selection will favour the evolution of male mate preference and thereby lead to males that invest heavily into reproduction being choosier than males that invest minimally. When male Limia were exposed to two females simultaneously, one from the small size class and one from the large size class, L. zonata chose large females over small ones, whereas L. perugiae allocated the same amount of time regardless of female size class. Although we fail to find support for our original hypotheses, our study highlights the need for a more thorough examination of non-model species like Limia. We suggest future studies analyse reproductive investment as it interacts with cryptic choice, multiple sensory cues as well as expand comparisons to multiple Limia species, especially those endemic to Cuba, Grand Cayman, and Jamaica.

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.

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.

A conceptual review of mate choice: stochastic demography, within-sex phenotypic plasticity, and individual flexibility

Mate choice hypotheses usually focus on trait variation of chosen individuals. Recently, mate choice studies have increasingly attended to the environmental circumstances affecting variation in choosers' behavior and choosers' traits. We reviewed the literature on phenotypic plasticity in mate choice with the goal of exploring whether phenotypic plasticity can be interpreted as individual flexibility in the context of the switch point theorem, SPT (Gowaty and Hubbell 2009). We found >3000 studies; 198 were empirical studies of within‐sex phenotypic plasticity, and sixteen showed no evidence of mate choice plasticity. Most studies reported changes from choosy to indiscriminate behavior of subjects. Investigators attributed changes to one or more causes including operational sex ratio, adult sex ratio, potential reproductive rate, predation risk, disease risk, chooser's mating experience, chooser's age, chooser's condition, or chooser's resources. The studies together indicate that “choosiness” of potential mates is environmentally and socially labile, that is, induced – not fixed – in “the choosy sex” with results consistent with choosers' intrinsic characteristics or their ecological circumstances mattering more to mate choice than the traits of potential mates. We show that plasticity‐associated variables factor into the simpler SPT variables. We propose that it is time to complete the move from questions about within‐sex plasticity in the choosy sex to between‐ and within‐individual flexibility in reproductive decision‐making of both sexes simultaneously. Currently, unanswered empirical questions are about the force of alternative constraints and opportunities as inducers of individual flexibility in reproductive decision‐making, and the ecological, social, and developmental sources of similarities and differences between individuals. To make progress, we need studies (1) of simultaneous and symmetric attention to individual mate preferences and subsequent behavior in both sexes, (2) controlled for within‐individual variation in choice behavior as demography changes, and which (3) report effects on fitness from movement of individual's switch points.

Do Males Form Social Associations Based on Sexual Attractiveness in a Fission-Fusion Fish Society?

Recent theory predicts that males should choose social environments that maximize their relative attractiveness to females by preferentially associating with less attractive rivals, so as to enhance their mating success. Using the Trinidadian guppy (Poecilia reticulata), a highly social species, we tested for non-random social associations among males in mixed-sex groups based on two phenotypic traits (body length and coloration) that predict relative sexual attractiveness to females and sexual (sperm) competitiveness. Based on a well-replicated laboratory dichotomous-choice test of social group preference, we could not reject the null hypothesis that focal males chose randomly between a mixed-sex group that comprised a female and a rival male that was less sexually attractive than themselves and another mixed-sex group containing a sexually more attractive male. The same conclusion was reached when females were absent from the two groups. As might be expected from these laboratory findings, free-ranging males in the field were not assorted by either body length or colour in mixed-sex shoals. The apparent lack of an evolved and expressed preference in wild male guppies from our study population to form social associations with other males based on their relative sexual attractiveness and competitiveness might be due to the fission-fusion dynamics of guppy shoals in nature. Such social dynamics likely places constraints on the formation of stable phenotype-based social associations among males. This possibility is supported by a simulation model which assumes group departure rules based on relative body size and coloration in males.

Evidence for cryptic speciation in directly transmitted gyrodactylid parasites of Trinidadian guppies

Cryptic species complexes are common among parasites, which tend to have large populations and are subject to rapid evolution. Such complexes may arise through host-parasite co-evolution and/or host switching. For parasites that reproduce directly on their host, there might be increased opportunities for sympatric speciation, either by exploiting different hosts or different micro-habitats within the same host. The genus Gyrodactylus is a specious group of viviparous monogeneans. These ectoparasites transfer between teleosts during social contact and cause significant host mortality. Their impact on the guppy (Poecilia reticulata), an iconic evolutionary and ecological model species, is well established and yet the population genetics and phylogenetics of these parasites remains understudied. Using mtDNA sequencing of the host and its parasites, we provide evidence of cryptic speciation in Gyrodactylus bullatarudis, G. poeciliae and G. turnbulli. For the COII gene, genetic divergence of lineages within each parasite species ranged between 5.7 and 17.2%, which is typical of the divergence observed between described species in this genus. Different lineages of G. turnbulli and G. poeciliae appear geographically isolated, which could imply allopatric speciation. In addition, for G. poeciliae, co-evolution with a different host species cannot be discarded due to its host range. This parasite was originally described on P. caucana, but for the first time here it is also recorded on the guppy. The two cryptic lineages of G. bullatarudis showed considerable geographic overlap. G. bullatarudis has a known wide host range and it can also utilize a killifish (Anablepsoides hartii) as a temporary host. This killifish is capable of migrating overland and it could act as a transmission vector between otherwise isolated populations. Additional genetic markers are needed to confirm the presence of these cryptic Gyrodactylus species complexes, potentially leading to more in-depth genetic, ecological and evolutionary analyses on this multi-host-parasite system.

Incomplete behavioural isolation and asymmetric female preference in darter sister species (Percidae: Etheostoma)

In this study, female preferences and behavioural isolation were estimated in a pair of allopatric sister species, Etheostoma duryi and Etheostoma flavum. Dichotomous mate preference trials were conducted to determine whether females prefer to associate with conspecific over heterospecific males and free-spawning assays were conducted to determine whether those preferences translated into behavioural isolation. Dichotomous mate choice trials revealed asymmetric female preference, as female E. flavum preferred conspecific males, whereas female E. duryi showed no preference. Free-spawning assays indicated that behavioural isolation remains incomplete between E. duryi and E. flavum (IB = 0·19). In addition to female mating preferences, male behaviour also appeared to influence mating outcomes as male E. flavum consistently courted conspecific females more often in free-spawning assays whereas male E. duryi did not. The data therefore suggest that despite marked divergence in male nuptial colour, divergence in female preferences between these species may not be sufficient to maintain species boundaries upon secondary contact. These results contrast with similar work in a sympatric darter species pair and may be explained by considering the contributions of reinforcement and differences in colour pattern as well as colour value.

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.

Molecular evidence for multiple paternity in a population of the Viviparous Tule Perch Hysterocarpus traski

Population density might be an important variable in determining the degree of multiple paternity. In a previous study, a high level of multiple paternity was detected in the shiner perch Cymatogaster aggregata, a species with high population density and a high mate encounter rate. The tule perch Hysterocarpus traski is phylogenetically closely related to C. aggregata, but it has relatively lower population density, which may result in distinct patterns of multiple paternity in these 2 species. To test the hypothesis that mate encounter rate may affect the rate of successful mating, we used polymorphic microsatellite markers to identify multiple paternity in the progeny arrays of 12 pregnant females from a natural population of tule perch. Multiple paternity was detected in 11 (92%) of the 12 broods. The number of sires per brood ranged from 1 to 4 (mean 2.5) but with no correlation between sire number and brood size. Although the brood size of tule perch is considerably larger than that of shiner perch (40.7 vs. 12.9, respectively), the average number of sires per brood in tule perch is much lower than that in shiner perch (2.5 vs. 4.6, respectively). These results are consistent with the hypothesis that mate encounter rate is an important factor affecting multiple mating.