Meeting Abstract

46.4  Jan. 6  Volume of song control nuclei in a songbird with near monomorphic song: Influences of sex and season JAWOR, Jodie*; MACDOUGALL-SHACKLETON, Scott, A.; University of Southern Mississippi, Hattiesburg, MS, USA; University of Western Ontario, London, Ontario, Canada jodie.jawor@usm.edu

Song production and learning is controlled in songbirds by a series of brain nuclei called the song control system (SCS). Many songbirds are strikingly sexually dimorphic in song production and SCS morphology; females typically possess smaller repertoires and SCS nuclei than males. Additionally, SCS nuclei volume can vary seasonally with larger volume in the breeding season; this has been linked to seasonally varying testosterone (T) levels. Here we report on sexual and seasonal differences in the SCS of northern cardinals (Cardinalis cardinalis) a species with nearly monomorphic song production. We also compared SCS volumes with levels of T in both sexes. Brains from 10 females and 10 males were collected prior to breeding (5 of each sex, no song in population) and early in the breeding season (5 of each sex, frequent song in population). SCS volume was determined from Nissl stained sections; T at the time of capture was determined via EIA. We found a significant sex by season effect on the volume of the song nucleus HVC; female HVC was smaller than male HVC and HVC in both sexes was smaller in the non-breeding season. There was no co-variation between T and HVC volume regardless of season. Our results suggest that even in species with near monomorphic song production female HVC is smaller. This may be linked to overall sexual differences in T levels in adults, or to hormone levels during development. Interestingly, even though male HVC volume differed with season, the level of change is not as large as that observed in other species. This may potentially allow male cardinals to have a prolonged period of song production, or produce song outside of the breeding season.