Meeting Abstract

P3.196  Monday, Jan. 6 15:30  Seasonal Patterns of Testosterone Production and Singing Behavior but not Variation in Song Control Region Volumes in Ramphocelus carbo (Thraupinae), an Endemic Amazon Songbird. QUISPE, R*; GAHR, M; Max Planck Institute for Ornithology rquispe@orn.mpg.de

In songbirds, the development and production of song are regulated by a network of interconnected brain nuclei known as the song control system. One central nucleus of this neural system is the HVC. The HVC functions as a sensorimotor integrator that projects to the descending motor pathway and to the anterior forebrain pathway involved in song learning. In several species, the HVC volume change seasonally, paralleling changes in the reproductive and singing activity. The HVC is sensitive to androgens and estrogens, and its size is thought to depend partly on circulating testosterone levels, being larger during the breeding season. Studies of high-latitude songbirds have served as important models for understanding the seasonal neuroplasticity of the song control system. However, in equatorial songbird species the mechanism seems to be different, as they are suppose to show a lower degree of seasonality in their annual cycles. In the equatorial lowland Amazon, there is little to no annual variation in photoperiod, but there are seasonal fluctuations in rainfall. In our study, we tracked changes in HVC volume and testosterone plasma level of male Silver-beaked Tanagers (Ramphocelus carbo) for one year in an equatorial population of the Brazilian Amazon. In addition we followed the singing activity of males during the transition from dry season to rainy season. Our results demonstrate a highly seasonal pattern in plasma testosterone levels and singing activity. Nevertheless, we found no significant variation in HVC volumes across the year. This study provides valuable information about the neuroplasticity, song behavior and significance of the environment on an endemic Amazon songbird.