Sexual signaling in the European bitterling: females learn the truth by direct inspection of the resource

In many taxa females appear to base their mate choice on multiple traits. But the relative importance of different traits in mate choice has rarely been determined. Here we show that females of a freshwater fish, the European bitterling, Rhodeus sericeus, base their mate choice on multiple traits that differ in their reliability as indicators of expected reproductive success and are used at different stages of the decision process. The initial decision to inspect a male is based on male behavior and red coloration, whereas the final spawning decision is based on the quality of the live unionid mussel, Anodonta anatina, that the male is defending as an oviposition site. Male traits may indicate which males are worth inspecting by reflecting male quality, such as reproductive condition and genetic constitution. Male traits do not, however, reflect mussel quality, as bright males also court females vigorously toward mussels that yield a low probability of survival of the offspring. Females, on the other hand, are choosier than males in their choice of spawning site and seem to gain reliable information about the survival probability of the eggs by inspecting the mussel directly.