Meeting Abstract
Population differences in migratory behavior and reproductive timing can lead to reduced gene flow and population divergence. Some migratory and sedentary (resident) populations that are sympatric in winter become allopatric after migration in a pattern of distribution known as heteropatry. If residents begin to breed prior to the departure of migrants, a window exists in which interbreeding may occur. In a previous study, male dark-eyed juncos from heteropatric populations were held in spring in a captive common garden, and migrants were shown to lag behind residents in testis size and testosterone. Far less is known about the impact of migration on the reproductive development of females, despite the obvious importance of female timing to gene flow. Although females rarely come into full reproductive condition in captivity, female European Starlings held on long-day photoperiod and exposed to multiple estradiol injections, exhibited elevated yolk proteins, an indicator of reproductive readiness. We predicted that migrant female juncos would be less responsive than residents to estradiol injections. We injected 38 females with estradiol for 5 days and then collected a blood sample. We sampled at two time points while females were held at a natural photoperiod of the wintering grounds: mid-March, prior to migration, and early May, during migration for migrants and early breeding season for residents. We sampled again in mid-June after all females had been advanced to a 16L: 8D photoperiod. Blood samples will be analyzed for triglycerides as indicators of VLDL, a female yolk protein. The data will bear on whether female reproductive readiness plays a role in the frequency of interbreeding between heteropatric populations, enabling us to better understand the role of migration in population divergence.
