Meeting Abstract
The energetic status of wild vertebrates can profoundly affect their reproductive system activity, but the mechanisms mediating these effects remain poorly understood. Addressing this issue, we investigated the reproductive system activity of captive adult male Abert’s Towhees, Melozone aberti, that were either subjected to mild chronic food restriction (FR) to decrease their body condition or fed ad libitum (CTRL), and were initially exposed to short days (SD) followed with transfer to long days (LD). The food restriction regime decreased the body mass, fat reserves, and pectoral muscle size. Transfer from SD to LD increased the size of the cloacal protuberance (a proxy for testis size) and plasma testosterone (T). These increases were similar in FR and CTRL birds, suggesting that food restriction does not limit photoinduced testicular growth or baseline T secretion. Under SDs, an injection either of gonadotropin-releasing hormone (GnRH) or of luteinizing hormone (LH) increased T in CTRL but not FR towhees. Thus, food restriction during SDs attenuated the pituitary gland and/or testis sensitivity to acute stimulation. During LD exposure, T increased in response to GnRH or LH challenge in both FR and CTRL birds. In addition, T increased more in CTRL than FR birds after LH, but not GnRH injection. This observation again suggests that the androgen response of the testes to LH stimulation is food availability- and/or energetic status-related. Collectively, the data identify food availability and/or energetic status as important factors modulating the sensitivity of the reproductive axis to GnRH or LH stimulation, and indicate that this modulation is day length-dependent. Support: ASU GPSA Award (S.D.) and NSF Award 1026620 (P.D.)
