The evolution of androgen receptor distribution in the spinal cord to support specialized sexual displays : a comparative analysis using a foot-flagging frog, Staurois parvus

This study examines the evolution of multimodal signaling behavior through a comparative investigation using three species--Staurois parvus, Rana pipiens, and Xenopus laevis. S. parvus is one of only about twenty frog species in the world that exhibits the communication signal known as foot-flagging, a conspicuous visual signal involving the outstretch of the frog’s hindlimb that evolved to attract female mates in the noisy environment in which they live. To regulate the production of this unique behavior, evolution might have coopted an existing mechanism in S. parvus physiology. Specifically, foot-flagging may have evolved along with androgen sensitivity of the spinal circuits controlling the foot, resulting in S. parvus having a significantly higher density of androgen receptor mRNA expression in lumbar areas of the spinal cord than both R. pipiens and X. laevis, two non foot-flagging species. However, results from this study indicate that there is no significant difference in the density of androgen receptor expression in spinal motor nucleus ten of the three species. Future studies should investigate the influence of androgens on aspects of the leg muscles involved in outstretching the hindlimb, including muscle fiber size and relaxation time between activation periods