Temporal variability in a multicomponent trait: nuptial coloration of female two-spotted gobies

Summary

Animals that breed more than once may face different environmental and physiological conditions at each reproductive event. Costs and benefits of sexual ornaments could therefore vary both within and between breeding seasons. Despite this, the ornaments are often assumed to be fixed, and temporal changes in ornamentation have rarely been investigated. Female two-spotted gobies (Gobiusculus flavescens) have colorful orange bellies when sexually mature and nest-holding males prefer females with more colorful bellies. This nuptial coloration is caused both by the carotenoids-rich gonads being directly visible through the skin and by the chromatophore pigmentation of the abdominal skin. Toward the end of the breeding season, males become rare and females become the more competitive sex. We show that female ornamentation of G. flavescens is a complex multicomponent trait and that the separate components, as well as their interactions, are variable. As gonads matured, they became more colorful while the abdominal skin became more transparent, causing more intense belly coloration in sexually mature females. However, coloration varied greatly also among fully mature females, suggesting that it may not only be a signal of readiness to spawn. Indeed, belly coloration predicted gonad carotenoid concentration, but there were several important seasonal differences in color expression. Females sampled toward the end of the breeding season were more colorful. This was due to seasonal increases in both gonad carotenoid concentration and skin coloration. Thus, at a time when competition over males is stronger and the terminal reproductive event approaches, females appear to invest more in signaling.