Sexual dimorphism and species differences in HVC volumes of cowbirds.
Cowbirds exhibit extensive variation in their social, territorial, and reproductive behaviors. Nissl-stained brain sections of specimens from a previous study (J. C. Reboreda, N. S. Clayton, & A. Kacelnik, 1996) were used to study the gross anatomy of a song control nucleus in 3 South American cowbirds (bay-winged, Molothrus badius; shiny, M. bonariensis; and screaming, M. rufoaxillaris). Cowbird high vocal center (HVC) volumes were consistently higher in males than in females in all 3 species. The largest HVC size of females found in bay-winged cowbirds is consistent with observations that females of this species, but not of the other 2 species, occasionally sing. The extent of the sexual dimorphism of relative HVC size was highest for the sexually dichromatic and promiscuous shiny cowbirds and smaller for the monochromatic and monogamous bay-winged and screaming cowbirds, suggesting that selection pressures associated with morphological traits and social systems are reflected in brain architecture.
Hauber
M E
ME
Field of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853-2702, USA. meh20@cornell.edu
Clayton
N S
NS
Kacelnik
A
A
Reboreda
J C
JC
DeVoogd
T J
TJ
D000818:Animals; D005260:Female; D008297:Male; D012737:Sex Factors; D012726:Sexual Behavior, Animal / Q000502:physiology*; D020308:Songbirds / Q000033:anatomy & histology* / Q000502:physiology; D013045:Species Specificity; D013687:Telencephalon / Q000033:anatomy & histology* / Q000502:physiology; D014828:Vocalization, Animal / Q000502:physiology*