Female Mate Choice Based on Male Nuptial Coloration in Pale Chub, Zacco platypus.

Males of many animals exhibit conspicuous secondary sexual traits, which are often the result of sexual selection. During the breeding period of the pale chub (Pisces: Cyprinidae), males show various sexual traits, such as long anal fins, breeding tubercles on the head, and/or conspicuous red and greenish-blue nuptial colorations. Although these conspicuous sexual dimorphisms and dichromatisms indicate that this can serve as a model species for understanding sexual selection, it is unclear whether these male sexual traits are related to female mate choice. This study examined the relationships between female mate choice and male sexual traits under laboratory conditions. In a dichotomous choice experiment, no relationship was found between female preference and male body size, anal fin length or number of breeding tubercles. In addition, female preference was not detected for traits related to the greenish-blue nuptial color of males. Instead, females chose males based on the degree of expression of red nuptial coloration. Such female preference may be useful for selecting high-quality males with good foraging abilities or good immune function related to carotenoids and sexual hormones. The present study suggests that red nuptial coloration of the male pale chub evolved in part through female mate choice.