MOORE, Ignacio T.; BENTLEY, George E.; WINGFIELD, John C.; BRENOWITZ, Eliot A.; Virginia Tech; University of Washington; University of Washington; University of Washington: Seasonal plasticity in the brain of a tropical bird
Seasonal changes in the brain mediate seasonal activities such as reproduction. At higher latitudes, seasonally breeding birds typically use changes in daylength to time these seasonal processes. In male birds, singing is often seasonal and serves to attract mates and defend territories. Seasonal singing and breeding behaviors are mediated by neural plasticity which includes growth of the neural song control system and increases in hypothalamic gonadotropin-releasing hormone (GnRH). These phenomena have been well documented in many northern latitude species, but have never been investigated in a tropical species despite the fact that the majority of bird species are tropical. Tropical environments experience changes in daylength that are relatively small and thus other environmental factors could be associated with seasonal breeding. We investigated whether seasonal plasticity in the brain exists in equatorial populations of Rufous-collared sparrows (Zonotrichia capensis), a congener of the intensively studied temperate white-crowned sparrow (Z. leucophrys). Rufous-collared sparrows breed seasonally on the equator where changes in rainfall are likely the primary environmental cue. During the breeding season, relative to the non-breeding season, male birds sing more and have higher plasma testosterone levels. Preliminary evidence suggests that the brains of these birds are plastic and related to breeding activity. Hypothalamic GnRH neurons are larger during the breeding season. Within the neural song control system, the nucleus HVC is significantly larger when breeding, with a similar trend in X, but no difference in RA. These results demonstrate that tropical birds can breed seasonally and exhibit associated plasticity in the brain in response to seasonal environmental cues other than photoperiod.
