Meeting Abstract

20.6  Jan. 5  Temporal effects of testosterone treatment on song control region growth in adult male House Finches STRAND, C.R.*; DEVICHE, P.; Arizona State University, Tempe christy.strand@asu.edu

In adult male songbirds, increases in circulating testosterone (T) levels and singing behavior induce the growth of specific brain regions that control singing behavior (song control regions; SCRs). However, in some species this growth occurs early in the breeding season, before significant changes in singing behavior occur and before maximal T levels are reached. Furthermore, birds in captivity have shown maximal growth of one SCR, the HVC, after one week of T treatment. The growth of the HVC is partially due to an increase in neuron number. To investigate the timing of the effect of T on the growth of the SCRs and singing behavior in adult male House Finches (Carpodacus mexicanus), we divided the birds into three groups: (1) Control group�no T; (2) 14 days of T treatment (14T); and (3) 21 days of T treatment (21T). To quantify singing behavior, birds were observed for 1 hour every other morning beginning on the fourth day of the experiment. Singing behavior was rare and was not influenced by T treatment. SCR volumes were larger than controls in the 21T group, while the 14T group was not different from either group. Similarly, there were more neurons in the HVC in the 21T group compared to controls, but not in the 14T group. SCR growth appears to occur slower in adult male House Finches in captivity, than in other species investigated. The �rapid� growth in other species is likely dependent on the combination of increased T and singing. The attenuated effect of T in the present experiment may be due to the lack of singing behavior. Thus, our results demonstrate effects of T on SCR growth independently of increases in singing behavior, which may help to identify the mechanisms of T alone on SCR growth.