Visual preference of males for conspecific mates in mutually ornamented fish: possible support for the species recognition hypothesis

Abstract

Because sexual selection typically acts on males, the evolution of conspicuous ornamentation in females has been insufficiently studied. Genetic correlation between the sexes and sexual or social selection on females have been proposed to explain female ornamentation, but they cannot fully explain certain patterns observed in nature such as female ornamentation in non-territorial, promiscuous species. The species recognition hypothesis, which postulates that ornamentation is adaptive because it prevents maladaptive hybridization, might plausibly explain female ornamentation. We examined this in two sympatric, non-territorial, promiscuous fish species, Tribolodon hakonensis (TH) and Tribolodon sachalinensis (TS), in which both sexes display species-specific conspicuous coloration in the breeding season. We conducted experiments on visual mate choice of male TH for conspecific and heterospecific females, and compared their association times. TH spent more time near conspecifics, indicating that they used visual cues to recognize them. Because the females of the two species presented to the males did not differ in body size, shape or behavior, male preference for conspecifics was probably based on female nuptial coloration. These results suggest that female ornamentation may evolve or be maintained not only by sexual or social selection within a species but also by interspecific interactions (e.g., hybridization).