Meeting Abstract

59.3  Wednesday, Jan. 6  Novel mechanisms regulating a sexual signal: testosterone inhibition of pheromone production in red-sided garter snakes PARKER, M ROCKWELL*; MASON, ROBERT T; Oregon State Univ., Corvallis parkermi@science.oregonstate.edu

Most vertebrates coordinate reproduction using multiple signals, but species that utilize single signals to encode multiple pieces of information are powerful models for understanding the regulation of signal production. Red-sided garter snakes utilize a single cue, the sexual attractiveness pheromone, to signal sex, season, condition, and reproductive state to conspecifics. This powerful sexual signal is regulated by estrogen: males given estrogen implants produce female sex pheromone. However, the presence of testicular androgens may inhibit pheromone production since castrated males produce low quality female sex pheromone. She-male garter snakes, naturally occurring males who produce a low quality female sex pheromone, have high aromatase activity in their skin resulting in local, feminizing estrogens. Since castrates exhibit the same “intermediate” pheromone phenotype as she-males, we tested the aromatase pathway hypothesis. We created seven experimental groups: SHAM, E2 (estrogen implant), GX (castrated), GX+ATD (aromatase inhibitor), FLUT (androgen inhibitor), T (testosterone), and GX+T. We found that castration induced attractivity (GX males were courted more than SHAM and wild males in the field), but blockage of aromatase activity in castrates (GX+ATD) resulted in unattractive males. The GX+T group was also unattractive, suggesting that T inhibits aromatase activity that can be induced by castration (T implants given a month post-castration). Collectively, we have shown that pheromone production in garter snakes is primarily signaled by estrogen, but these results suggest testosterone actively inhibits a quiescent pathway involving aromatase that may be the underlying source of sexual signal evolution in this system.