Meeting Abstract
14.5 Sunday, Jan. 4 Interactions of testosterone and paternal care in a tropically breeding sparrow LYNN, S. E.*; PRINCE, L. E. ; SCHOOK, D. E. ; MOORE, I. T. ; The College of Wooster; The College of Wooster; The College of Wooster; Virginia Tech slynn@wooster.edu
In most male birds that exhibit paternal care, elevated testosterone (T) reduces nestling provisioning, which can be detrimental to offspring survival. Two mechanisms may enable some males to avoid this potentially detrimental effect of responding to elevated T: (1) decreased sensitivity to Ts effects on behavior, and/or (2) decoupling of T secretion from territorial challenges. Both mechanisms have been documented, however whether selection for them is correlated or independent is unknown. We investigated the relationship of elevated T and paternal care in a tropical bird, the rufous-collared sparrow (Zonotrichia capensis). Z. capensis have a flexible breeding season and smaller clutch size than temperate congeners. Males also do not increase plasma T in response to territorial challenges. We implanted males with T or empty implants, and later observed paternal behavior 2-3 and 6-7 days post-hatch. During both observation periods, control males fed chicks significantly more often than T-implanted males. In fact, 100% of control males fed chicks during both observation periods, whereas 22% and 0% of T-implanted males fed chicks on days 2-3 and 6-7, respectively. Chicks of T-implanted males weighed less than control chicks, but tarsus growth, wing growth, and fledging success did not differ. Thus, we demonstrate a robust negative effect of T on nestling provisioning that may not impact reproductive success. Some of the differences we describe between this tropical bird and previous studies on higher latitude species may relate to life history characteristics of tropical breeders, including extreme flexibility in breeding schedule and small clutch size. Our data also suggest selection for mechanisms to avoid the costs of elevated T during the parental phase occurs independently.
