Meeting Abstract

P1.208  Friday, Jan. 4  Melatonin and the reproductive axis of European starlings GUARDADO , D*; BENTLEY, G.E; PERFITO, N; University of California, Berkeley ; University of California, Berkeley ; University of California, Berkeley daisy.guard@gmail.com

Melatonin is secreted by the pineal gland at night and thus, for many organisms it provides a measure of day length throughout the year. Day length information is critical for seasonal breeders to time changes in their reproductive physiology that are costly in terms of time and energy. The melatonin signal in seasonally breeding mammals is essential for appropriate timing of changes in gonadal size and activity. Such a dependence upon the melatonin signal for reproductive timing is not as clearly defined in birds. Despite a handful of studies to the contrary, the current dogma is that melatonin does not influence the reproductive axis in birds. In our study, we investigated the effects of exogenous melatonin on the reproductive axis of European starlings (Sturnus vulgaris) housed in a semi-natural environment. Male and female adult starlings were given melatonin or control silastic implants during naturally increasing long days (March) and a second group of each sex was given implants or controls after the breeding season had ended but still during long days (August). Melatonin treatment did not affect testis volume or follicle development during either time period. Melatonin implants increased hypothalamic expression of GnIH only in photorefractory starlings. In addition, hypothalamic expression of GnRH, a stimulatory reproductive hormone, was not affected by treatment in either group, although it did change according to season. This study aims to understand how starlings under natural breeding conditions respond to exogenous melatonin and how this response relates to previous knowledge from laboratory studies.