Age- and sex-related variation in song-control regions in Cassin's finches, Carpodacus cassinii.
Male Cassin's finches (Carpodacus cassinii) sing long, complex songs that incorporate many elements mimicked from other species. Although one-year-old males (males in their first breeding season) are sexually competent and do breed, they sing a simpler song (fewer syllable types) than do males two or more years old (called after-second-year males). Females do occasionally sing, but with much less stereotypy and complexity than breeding males of any age. We collected brains from free-living breeding after-second-year males (identified by their red plumage), one-year-old males (identified by their female-like brown plumage), and adult females to examine sex- and age-related differences in three song-control nuclei: HVC, Area X and RA. Nuclei volumes were reconstructed by measuring the Nissl-defined area in every second section. There was a large sex difference in all three nuclei, with female volumes 40-50% that of males. There was no difference in HVC volume between age classes of males. However, one-year-old (brown) males had significantly larger Area X volume than did the older (red) males, with red males' Area X about 75% the volume of brown males'. These data raise questions regarding the functional significance of Area X and related nuclei in relation to song development in vocal mimics.
Macdougall-Shackleton
Scott A
SA
Department of Psychology, University of Western Ontario, London, ON N6A 5C2, Canada. smacdou2@uwo.ca
Ball
Gregory F
GF
Edmonds
Eric
E
Sul
Raeme
R
Hahn
Thomas P
TP
D000367:Age Factors; D000818:Animals; D005260:Female; D046369:Finches / Q000033:anatomy & histology* / Q000502:physiology; D008297:Male; D009929:Organ Size; D012727:Sex Characteristics; D013687:Telencephalon / Q000033:anatomy & histology* / Q000502:physiology; D013737:Testis / Q000033:anatomy & histology / Q000502:physiology; D014828:Vocalization, Animal / Q000502:physiology*