Effects of experimentally elevated testosterone on plasma glucocorticoids,body mass, and recapture rates in yellow-pine chipmunks, Tamias amoenus

In male yellow-pine chipmunks plasma levels of glucocorticoids (GCs) are lo w while plasma testosterone (T) levels peak during the mating season, sugge sting that T suppresses GC levels. To test this hypothesis, free-living, po st-reproductive males were implanted during summer with either a T-filled ( T-males) or an empty silastic implant (controls or C-males). Body mass and plasma levels of corticosterone, cortisol, and T were measured immediately before and 1 month after implantation. Exogenous testosterone increased T t o high physiological levels typical of reproductively active males. By 1 mo nth after implantation, T-males decreased their mean body mass and plasma G C levels, while C-males maintained their mean body mass and GC levels. Even though T-males lost mass, recapture success 1 month after implantation for T-males (71%) was equal to that of C-males (71%). However, the overwinter recapture rate of C-males (83%) was significantly greater than that of T-ma les (20%). The results support the hypothesis that high plasma T of males d uring mating has a suppressive effect on plasma GC levels. Additionally, ex perimentally elevated T significantly reduced the rate of recapture during the following spring, and this may reflect a reduction in local overwinter survival. The suppression of adrenocortical activity by T may contribute to the reductions in prehibernation body mass and post-emergence recapture su ccess. J. Exp. Zool. 287:378-383, 2000. (C) 2000 Wiley-Liss, Inc.