A common endocrine signature marks convergent evolution of an elaborate dance display in frogs

Unrelated species often evolve similar phenotypic solutions to the same environmental problem, a phenomenon known as convergent evolution. But, how do these 'common traits' arise? We address this question from a physiological perspective by assessing how convergence of an elaborate gestural display in frogs ("foot flagging") is linked to changes in the androgenic hormone systems that underlie it. We show that the emergence of this rare display in unrelated anuran taxa is marked by a robust increase in the expression of androgen receptor (AR) mRNA in the musculature that actuates leg and foot movements, but we find no evidence of changes in abundance of AR expression in these frogs' central nervous system (CNS). Meanwhile, the magnitude of the evolutionary change in muscular AR and its association with the origin of foot flagging differ among clades, suggesting that these variables evolve together in a mosaic fashion. Finally, while gestural displays do differ between species, variation in the complexity of a foot-flag routine does not predict differences in muscular AR. Altogether, these findings suggest that androgen-muscle interactions provide a conduit for convergence in sexual display behavior, potentially providing a 'path of least resistance' for the evolution of motor performance