Sexual Dichromatism and Temporary Color Changes in the Reproduction of Fishes

SYNOPSIS. Studies on color patterns of fishes have focused on relationships between bright, relatively permanent colors, such as those of fishes inhabiting coral reef and tropical freshwater habitats, and ecological factors, such as competitors, predators, and the visual background. By comparison, the functions of, and hence the selective pressures acting on, temporary changes in nuptial coloration have received much less attention. Temporary color changes associated with reproduction occur in many freshwater and marine groups. Nuptial coloration in fishes functions both in agonistic interactions among males and courtship of females, so that it is subject to both intrasexual and intersexual selection as well as natural selection. Temporal variation in nuptial color patterns is sensitive to temporal changes in the male's physical condition, motivation, and social status. Physiological processes, such as neuronal and endocrine changes, play important roles in the expression of breeding colors, including rapid responses to changes in social conditions. The importance of proximal mechanisms and ultimate selective processes in mediating rapid changes in the blue, melanin—based breeding colors of pupfish, and the red, carotenoid—based color patterns in guppies are discussed in the context of signal function and evolution.