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Variation in mating preferences coupled with selective predation may allow for the maintenance of alternative mating strategies. Males of the South American live‐bearing fish Poecilia parae fall in one of five discrete morphs: red, yellow, blue, stripe‐coloured tail (parae) and female mimic (immaculata). Field surveys indicate that the red and yellow morphs are the rarest and that their rarity is consistent across years. We explored the role of variable female mating preference and selective predation by visual predators in explaining the rarity of red and yellow males, and more generally, the maintenance of this extreme colour polymorphism. We presented wild‐caught P. parae females and Aequidens tetramerus, the most common cichlid predator, with the five male colour morphs in separate trials to determine mating and prey preferences, respectively. We found that a large proportion of females shared a strong preference for the rare carotenoid‐based red and yellow males, but a distinct group also preferred the blue and parae morphs. The cichlid predator strongly preferred red and yellow males as prey. Together, these results suggest that the interaction between premating sexual selection favouring and predation acting against the red and yellow morphs may explain their rarity in the wild. The trade‐off between sexual and natural selection, accompanied by variation in female mating preferences, may therefore facilitate the maintenance of the striking colour polymorphism in P. parae.

The conspicuousness of animal signals is influenced by their contrast against the background. As such, signal conspicuousness will tend to vary in nature because habitats are composed of a mosaic of backgrounds. Variation in attractiveness could result in variation in conspecific mate choice and risk of predation, which, in turn, may create opportunities for balancing selection to maintain distinct polymorphisms. We quantified male coloration, the absorbance spectrum of visual pigments and the photic environment of Poecilia parae, a fish species with five distinct male color morphs: a drab (i.e., grey), a striped, and three colorful (i.e., blue, red and yellow) morphs. Then, using physiological models, we assessed how male color patterns can be perceived in their natural visual habitats by conspecific females and a common cichlid predator, Aequidens tetramerus. Our estimates of chromatic and luminance contrasts suggest that the three most colorful morphs were consistently the most conspicuous across all habitats. However, variation in the visual background resulted in variation in which morph was the most conspicuous to females at each locality. Likewise, the most colorful morphs were the most conspicuous morphs to cichlid predators. If females are able to discriminate between conspicuous prospective mates and those preferred males are also more vulnerable to predation, variable visual habitats could influence the direction and strength of natural and sexual selection, thereby allowing for the persistence of color polymorphisms in natural environments.

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Whenever males can monopolize females and/or resources used by females, the opportunity for sexual selection will be great. The greater the variation among males in reproductive success, the greater the intensity of selection on less competitive males to gain matings through alternative tactics. In the yellow dung fly, Scathophaga stercoraria, males aggressively compete for access to receptive, gravid females on fresh dung. Larger males are better able to acquire mates and to complete copulation successfully and guard the female throughout oviposition. Here we demonstrate that when an alternative resource is present where females aggregate (i.e. apple pomace, where both sexes come to feed), smaller males will redirect their searching for females from dung to the new substrate. In addition, we identify a class of particularly small males on the alternative substrate that appears never to be present searching for females on or around dung. Smaller males were found to have a mating 'advantage' on pomace, in striking contrast to the pattern observed on dung, providing further support for the existence of an alternative male reproductive tactic in this species.

BackgroundIntense competition for access to females can lead to males exploiting different components of sexual selection, and result in the evolution of alternative mating strategies (AMSs). Males of Poecilia parae, a colour polymorphic fish, exhibit five distinct phenotypes: drab-coloured (immaculata), striped (parae), structural-coloured (blue) and carotenoid-based red and yellow morphs. Previous work indicates that immaculata males employ a sneaker strategy, whereas the red and yellow morphs exploit female preferences for carotenoid-based colours. Mating strategies favouring the maintenance of the other morphs remain to be determined. Here, we report the role of agonistic male-male interactions in influencing female mating preferences and male mating success, and in facilitating the evolution of AMSs.ResultsOur study reveals variation in aggressiveness among P. parae morphs during indirect and direct interactions with sexually receptive females. Two morphs, parae and yellow, use aggression to enhance their mating success (i.e., number of copulations) by 1) directly monopolizing access to females, and 2) modifying female preferences after winning agonistic encounters. Conversely, we found that the success of the drab-coloured immaculata morph, which specializes in a sneak copulation strategy, relies in its ability to circumvent both male aggression and female choice when facing all but yellow males.ConclusionsStrong directional selection is expected to deplete genetic variation, yet many species show striking genetically-based polymorphisms. Most studies evoke frequency dependent selection to explain the persistence of such variation. Consistent with a growing body of evidence, our findings suggest that a complex form of balancing selection may alternatively explain the evolution and maintenance of AMSs in a colour polymorphic fish. In particular, this study demonstrates that intrasexual competition results in phenotypically distinct males exhibiting clear differences in their levels of aggression to exclude potential sexual rivals. By being dominant, the more aggressive males are able to circumvent female mating preferences for attractive males, whereas another male type incorporates subordinate behaviours that allow them to circumvent male aggression and female mating preferences. Together, these and previous results indicate that exploiting different aspects of social interactions may allow males to evolve distinct mating strategies and thus the long term maintenance of polymorphisms within populations.

Male secondary sexual traits of animals are richly diversified in form and complexity, yet there are many species in which their precise function remains unknown. Within the genus Drosophila, species belonging to the melanogaster and obscura species groups have evolved a remarkable variety of sex combs, male‐limited secondary sexual traits located on the tarsi of both front legs. Information concerning sex comb function is minimal or absent, except for D. melanogaster, where previous studies indicate that the sex combs are used for grasping the female prior to copulation. These studies, however, do not unambiguously demonstrate comb function, because it has not been possible to ascribe observed behavioral outcomes of the various comb manipulations to changes in the combs per se. We used microscale laser surgery to manipulate comb size in D. melanogaster and D. bipectinata, and tested the hypothesis that the sex combs function as grasping devices in courtship, making them essential for copulation to ensue. Results of high‐resolution behavioral analysis in small observation arenas demonstrated that in both species in which sex combs were surgically eliminated, males were unable to grasp, mount or copulate. The combless foretarsi of these altered males slipped off the end (D. melanogaster) and sides (D. bipectinata) of the female abdomen when courting males attempted to grasp. In most cases, males whose sex combs were reduced but not completely removed exhibited similar copulation probabilities as surgical control males, a result we demonstrated in observation chambers as well as under more ecologically realistic conditions inside population cages where males and females interacted on the surface of fruit substrates. Thus, the sex combs in D. melanogaster and D. bipectinata are grasping devices, essential for mounting and copulation.

Background. Gold mining activities in forested areas across Guyana have been a common practice for more than a century. The intensification of artisanal and small-scale gold mining (ASGM) in recent decades caused by global market demand is contributing to the mobilization of mercury into aquatic systems. Indigenous populations who consume high levels of locally sourced fish are greater at risk for methylmercury poisoning from ingestion of contaminated fish. Objectives. The aim of the present study was to investigate the levels of mercury contamination and identify the risk factors associated with hair mercury levels in four indigenous communities in Guyana. Methods. Concentrations of total mercury were measured in hair samples from 99 participants from four indigenous communities in the south Rupununi region in Guyana. The findings of this study were compared with those of previous studies to assess the prevalence of mercury contamination in indigenous communities across Guyana. Results. Hair mercury levels were found to be above the World Health Organization (WHO) reference value for residents who live close to ASGM activities and who consume high quantities of locally sourced fish. Our results are not only consistent with those obtained in previous studies, but also evidence that mercury poisoning has become a generalized problem for indigenous communities in Guyana. Conclusions. Fish is the main source of protein for many riverine communities and consumption of mercury-contaminated fish poses a serious health hazard for these vulnerable populations. The situation is especially dire for community members of Parabara with 100% of participants showing elevated (>15 μg*g−1) hair mercury levels. It is therefore crucial that Parabara residents be evaluated by relevant health agencies for clinical symptoms related to mercury toxicity. Participant Consent. Obtained Ethics Approval. The study protocol was approved by the Institutional Review Board of the Ministry of Public Health, Guyana. Competing Interests. The authors declare no competing financial interests.