Meeting Abstract
The life-history trade-off between self-maintenance and reproduction is mediated by two hormonal networks: the hypothalamic-pituitary-adrenal axis (HPA), which mediates the stress response, an essential aspect of self-maintenance, and hypothalamic-pituitary-gonadal axis (HPG), which mediates reproduction. HPA and HPG have a capacity for a significant crosstalk, and, under some environmental conditions, activation of the HPA can suppress the HPG, potentially interfering with reproduction. If we are to predict how animals will respond to environmental changes that alter this trade-off, we need to know more about how the HPA and HPG interact. We experimentally investigated whether chronic disturbance affects gonadal development and the gonad’s ability to produce and release testosterone (T) in a songbird, the Dark-eyed Junco (Junco hyemalis). In the high-disturbance treatment, captive males were repeatedly exposed to stressors for three weeks; controls were undisturbed except for animal husbandry. To assess impact of disturbance on the HPG, we measured baseline levels of testosterone (T) in peripheral blood within 5 min of capture, and gonadal capacity to produce T 30 min after an injection with GnRH. We then measured gonadal mass and gene expression related to the signaling of the HPG. Birds in the high-disturbance treatment showed significantly lower baseline T levels than control birds. However, neither GnRH-induced levels nor gonadal mass showed significant differences between treatments, suggesting that the gonadal capacity to produce T is not affected by disturbance. We conclude that high levels of disturbance in the wild may reduce expression of T and T-mediated traits. Analysis of gonadal gene expression will shed light on the mechanisms by which disturbance affects HPG function.
