Meeting Abstract
Nutrition influences reproductive functions across vertebrates, but the effects of food availability on the functioning of the hypothalamic-pituitary-gonadal (HPG) axis and the mechanisms mediating these effects in wild birds remain unclear. We investigated the influence of mild chronic food restriction on the HPG axis of photostimulated House Finches (Haemorhous mexicanus). Food-restricted birds had underdeveloped testes with smaller seminiferous tubules than control (ad libitum fed) birds. Baseline plasma testosterone (T) increased in response to photostimulation in control but not in food-restricted birds. However, food availability did not affect the plasma T increase resulting from a gonadotropin-releasing hormone (GnRH) or a luteinizing hormone (LH) challenge. Thus, decreased testis size and low plasma T secretion during food restriction did not result from decreased sensitivity of the pituitary gland to GnRH or of the testes to LH. The number of hypothalamic GnRH-I immunoreactive cells was higher in food-restricted than control finches, suggesting accumulation from non-release. Food availability did not influence plasma CORT, indicating that the observed HPG axis inhibition did not follow increased activity of the hypothalamic-pituitary-adrenal axis. This study is among the first to examine multilevel functional changes in the HPG axis in response to food restriction in a wild bird. The results indicate that food availability affects both hypothalamic and gonadal function and further investigations are needed to clarify the mechanisms by which nutritional signals mediate these effects. Supported by National Science Foundation Award 1026620 to P.D.
