Alternative mating strategies may favour the persistence of a genetically based colour polymorphism in a pentamorphic fish

Abstract

Males of the pentamorphic fish, Poecilia parae , show a striking colour polymorphism that ranges from drab coloration resembling females to brilliant black and red stripes. We tested the hypothesis that the observed polymorphism may persist because each morph uses a unique but equally successful mating strategy. We quantified the mating behaviour, testes investment and sperm morphometrics of each morph. We found that the smallest morph (immaculata), which resembles drab females, used a ‘sneaker’ tactic (i.e. forgoing courtship and mostly ‘stealing’ copulations) as a mating strategy. Immaculata males also had larger testes, and produced larger ejaculates and sperm with longer flagella, which should provide advantages during sperm competition. The largest morph (parae) and the coloured blue, red and yellow morphs used a combination of courtship and sneaker tactics. However, they achieved greater copulation success as a result of courtships. The testes investment of parae and yellow morphs were similar but larger than those of the blue and red males. Our results suggest that male morphs of the pentamorphic Poecilia parae use unique mating strategies that exploit different aspects of pre- and postcopulatory sexual selection, which, in turn, may help maintain their relatively stable frequencies in the wild.