A ROLE FOR RECEIVER BIAS IN ROSE BITTERLING MATE CHOICE?

Abstract

The evolution of costly secondary sex traits in males may arise as a result of male-male competition or female mate choice. Female mating decisions may be associated with either direct or indirect benefits, and may evolve as a consequence of selection for signal detection in a non-mating context. We raised fish in the laboratory fed only on green coloured food and subsequently tested their foraging preferences by presenting them with plastic strips of different colours and recording the number of bites directed at each. We conducted separate tests on juveniles and sexually mature fish, and compared the responses of males and females. Male rose bitterling (Rhodeus ocellatus) display red, carotenoid-based nuptial colouration but its function in the mating system is unclear; there is little evidence that male colour plays a role in female mating decisions although there is a weak relationship between colour and dominance among males. We tested for a bias towards red in a non-mating context and found that bitterling show a strong response to red food items, irrespective of age, sex or prior experience. This correlation between a sexually selected trait and an intrinsic attraction to red appears to support the receiver bias hypothesis for the evolution of red nuptial colouration in bitterling. We discuss how this trait could be maintained under sexual selection in the absence of strong preference or any obvious fitness benefits.