Meeting Abstract
Gonadal steroids, such as testosterone (T), mediate many reproductive and social behaviors in vertebrates. It is therefore useful to experimentally manipulate T levels in order to investigate how these hormone-mediated traits may be shaped by selection. One commonly used method to temporarily increase T within physiological ranges is to stimulate the hypothalamo-pituitary-gonadal (HPG) axis with injections of gonadotropin-releasing hormone (GnRH). However, despite their frequent use as an assay of HPG axis reactivity, the effects of GnRH injections on behavior are poorly understood. Here, we tested the effects of GnRH vs. saline injections on parental care in free-living male tree swallows (Tachycineta bicolor) during the chick rearing period. To measure effects on paternal care in the 24 h post-injection, we quantified RFID-logged nest visitation rate (i.e. provisioning) and nestling growth. Because prior work suggests that T often suppresses paternal care in songbirds, we expected to find temporarily reduced care in GnRH males vs. saline males. Surprisingly, we found the opposite: GnRH-injected males visited their nest boxes significantly more than controls, and their chicks tended to grow faster. Additionally, the degree to which males elevated T in response to GnRH positively correlated with the rate at which their chicks grew. Together, these data suggest that males experiencing a surge in T, or some other GnRH-controlled hormone, provision more than controls. Results also highlight the utility of GnRH challenges, which can temporarily elevate gonadal steroids within physiological limits and, in doing so, reveal behavioral and performance-related consequences of naturalistic hormonal fluctuations.
