Poster Presentation The International Congress of Neuroendocrinology 2014

Increased hypothalamic-pituitary-adrenal axis activity may facilitate transition into active breeding (#216)

Molly J Dickens 1 , George E Bentley 2
  1. Integrative Biology, University of California, Berkeley, Berkeley, CA, USA
  2. Integrative Biology and Helen Wills Institute for Neurobiology, University of California, Berkeley, Berkeley, CA, USA

That the hypothalamic pituitary adrenal (HPA) axis regulates the glucocorticoid response to stress is well known.  Less understood is the role that seasonal increases in HPA activity play in facilitating reproduction; i.e., do they underlie the physiological transition to active breeding or are they symptomatic of increased physiological demands at that time? In this study, wild caught male and female European starlings (n=12 per sex) were housed outdoors in a large, semi-natural environment. Early in the breeding season, half of the birds were moved into a smaller, indoor flight aviary. Although they were provided with nest boxes, nesting material and natural light, indoor birds did not progress into active breeding as the outdoor birds did. Each nest box outdoors was occupied by a pair and nests were complete or near complete, but indoors, only one nest (of six) neared completion. Half of the outdoor females were laying or preparing to lay eggs while no indoor females showed evidence for laying preparedness. Outdoor males had significantly lower circulating testosterone (0.07+/-0.03ng/mL) compared to indoor males (1.3+/-0.4ng/mL). We had predicted that transferring birds to the indoor setting would result in dysregulation of the HPA axis, and thus disruption of reproduction, due to chronic stress associated with the captive environment. We observed increases in baseline and stress-induced corticosterone in the outdoor birds, while the indoor birds showed no changes in these measurements. We hypothesize that the sudden increase in HPA activity outdoors facilitates the transition into active breeding and captivity affects reproduction by inhibiting this seasonal shift in HPA response.  We present neural and gonadal gene expression data that provide insight to the potential mechanisms underlying this phenomenon.