Meeting Abstract

P2.27  Monday, Jan. 5  Breeding variation of testosterone in the high latitude Rufous-collared sparrow, Zonotrichia capensis australis ADDIS, E.A.*; CLARK, A.D.; VASQUEZ, R.; WINGFIELD, J.C.; University of Washington, Seattle; University of Washington, Seattle; Universidad de Santiago, Chile; University of California, Davis addise@u.washington.edu

In vertebrates, testosterone regulates many aspects of reproductive function. In birds, testosterone is important for sperm production and the development of some secondary sex characteristics, including activation of sexual behavior and territorial aggression. The challenge hypothesis addresses trade-offs between circulating levels of testosterone and male breeding behavior in birds. Two important postulates of the challenge hypothesis are (1) testosterone levels are high during periods of social instability and territory establishment when male-male interactions are common and (2) testosterone levels decrease during the parental phase of breeding if males exhibit substantial parental care. Most tests of the challenge hypothesis have been conducted in northern temperate and arctic birds. Investigations of the Rufous-collared sparrow (Zonotrichia capensis) in Ecuador and Costa Rica show no correlation between testosterone and aggressive behavior, suggesting a decoupling of testosterone and aggression. To further explore this seeming discrepancy, we tested the challenge hypothesis in a subspecies of the Rufous-collared sparrow, Z.c.australis, breeding at high latitude in the southern hemisphere. These results were additionally compared with our previous exploration of testosterone and aggression in the Rufous-collared sparrow at mid-latitudes of the southern hemisphere.