Intrasexual competition facilitates the evolution of alternative mating strategies in a colour polymorphic fish

Abstract

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.

Prenatal exposure to low doses of atrazine affects mating behaviors in male guppies

“…When competition is high, males will invest more in forced copulations (Jirotkul, 1999) and aggressive behaviors, and focus less on courtship; this was apparent from the low numbers of males that performed courtship displays in the presence of a rival male in this study. Aggression between rival males is an important factor in gaining fertilizations because winning contests allows access to females (Bertram et al, 2011;Brown et al, 2007;Hurtado-Gonzales and Uy, 2010). More aggressive males will also guard mates to prevent sperm competition (Bateman and Toms, 1998;van Dongen, 2008;Watts, 1998).…”

“…Males may also gain some fertilizations by employing other strategies like forced copulations (Clutton-Brock and Parker, 1995). In species with high male-male competition, aggression between competing males may be a factor influencing access to females and monopoly of fertilizations (Bertram et al, 2011;Brown et al, 2007;Hurtado-Gonzales and Uy, 2010). Males performing sub-optimally in any of these mating behaviors will suffer reduced mating and reproductive success.…”

Close encounters of the three morphs: does color affect aggression in a polymorphic lizard?

“…One of the mechanisms that can help to maintain variation in a population is negative frequencydependent selection resulting from some processes, such as predation (Olendorf et al 2006;Qvarnström et al 2012), sexual selection (Sinervo and Lively 1996) and intraspecific competition (Seehausen and Schluter 2004), that guarantee an advantage to rare morphs. Morphs often adopt alternative strategies that are an outcome of male-male competition and maintain genetic variation and enhance the reproductive success of each morph under context-dependent control (Bleay et al 2007;Hurtado-Gonzales and Uy 2010). In this scenario, males of rare morphs should receive less aggression from other males, because they do not share the same resources, and thereby they should experience a fitness advantage (Seehausen and Schluter 2004;Qvarnström et al 2012).…”

Extreme Y chromosome polymorphism corresponds to five male reproductive morphs

“…Previous work suggests that P. parae morphs are also under negative frequency dependent selection [14][15][16][17] , and this could facilitate the establishment and maintenance of five distinct Y chromosomes within the same species. Most new mutations are expected to be lost through drift if they do not confer a high enough fitness advantage over alternative alleles 63 , but mutations resulting in a new morph would be at the lowest frequencies and thus have the highest fitness, allowing them to rapidly stabilize in the population.…”

“…Remarkably, males of this species are one of five distinct morphs that utilize different reproductive tactics, and differ in reproductive strategy, body size, color, and mating behaviour [13][14][15][16][17][18][19] (summarized in Table S1). There are three major morphs: parae, immaculata and melanzona.…”