Meeting Abstract
When migratory and sedentary populations co-occur, they experience the same biotic and abiotic cues, yet migratory individuals prepare for migration while sedentary individuals prepare to breed. The co-occurrence of migratory and sedentary populations during winter and early spring, a form of heteropatry, provides a unique opportunity for identifying the neuroendocrine mechanisms that regulate the timing of reproduction and migration. In a common garden experiment we tested 1) whether co-occurring migratory and sedentary male dark-eyed juncos (Junco hyemalis) maintain reproductive timing differences when held captive under natural photoperiod with abundant food, 2) whether seasonal elevation of circulating corticosterone (CORT) in migrants in early spring is associated with delayed reproduction and 3) whether and which genes are differentially expressed in migratory and sedentary juncos in early spring. To address these questions we compared the migratory and sedentary groups for circulating levels of testosterone (T), T in response to exogenous GnRH, circulating CORT, and differential gene expression in blood and pectoral muscle in early spring. We discuss our results, and the mechanisms regulating the timing of migration and breeding, in light of rapid climate change.
