Meeting Abstract

P2.135  Tuesday, Jan. 5  Population differences in reproductive biology of free-living Cassin’s Sparrows, Aimophilla cassinii. HURLEY, LL*; DEVICHE, P; Arizona State Univ. llhurley@asu.edu

Seasonally breeding birds use various proximate cues to regulate their reproductive cycle. In relatively stable seasonal environments, the primary cue used often is day length. In less predictable environments such as Southwest USA deserts, supplementary factors associated with weather (e.g., monsoon precipitation) may also play an important role. Little is known regarding the specific role and mechanisms by which effects of these factors are integrated to regulate the activity of the reproductive system. To begin addressing this question, we compared seasonal changes in reproductive morphology (testis size and cloacal protuberance: CP) and molt in Cassin’s Sparrows, Aimophila cassinii, belonging to two geographically separate populations (Arizona and Colorado) that employ temporally different breeding strategies: Colorado birds breed in spring whereas Arizona birds initiate breeding in response to summer monsoon-associated environmental changes. These populations were found to exhibit quantitatively similar time courses of seasonal changes in testis and CP sizes as well as prebasic (post-breeding) molt, but exhibited a temporal shift in breeding activity so dramatic that Colorado birds were in the first stages of prebasic molt when Arizona birds were just becoming reproductively active. We are currently conducting additional experiments aimed at determining the neuroendocrine basis of these intraspecific population shifts in seasonal reproductive timing.