Keisuke Atsumi, Osamu Kishida, Itsuro Koizumi

Because sexual selection typically acts on males, evolution of conspicuous ornamentation in females has been understudied. Genetic correlation between sexes and sexual or social selection on females have been proposed to explain female ornamentation, but they cannot fully explain observed patterns 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 the possibility of this hypothesis in two sympatric, non-territorial, promiscuous fish species. Both sexes of Tribolodon hakonensis and T. sachalinensis display species-specific conspicuous coloration in the breeding season. We conducted visual-based mate choice experiments using T. hakonensis males and compared their association times between conspecific and heterospecific females. Males spent more time near conspecifics, indicating that T. hakonensis males used visual cues to recognize conspecifics. Because the females presented to the males did not differ in body size, shape and behavior between the two species, the male preference for conspecifics was probably based on the females nuptial coloration. These results suggest that female ornamentation may evolve or be maintained by not only sexual or social selection within a species but also interspecies interactions (e.g. hybridization).