Condition dependence of advertisement calls in male African clawed frogs

Abstract

Variations in the costs or benefits of signaling may result in variations in signaling strategies. The adverse conditions hypothesis suggests that reliable signaling can be improved under stress or adverse environmental conditions, but the empirical cases are limited. In the present study, we manipulated food availability in male Xenopus laevis in order to determine whether certain characteristics of advertisement call in X. laevis are condition-dependent and how food depletion modulates the association between individual condition and signaling performance. The results showed that although frogs tend to decrease their within-bout call rate compared to other call characteristics (calling effort and dominant frequency) under food constraint, none of them was statistically significantly affected by food restriction. However, within-bout call rate was positively coupled with adaptive immunocompetence in starved frogs, and the correlation was decoupled in those with free access to food. These results support that within-bout call rate is a condition-dependent characteristic of advertisement call and even mild adverse conditions may enhance reliable signaling in X. laevis, probably due to enlarging the relative fitness difference between high- and low-condition individuals.