Meeting Abstract
Animal migration can lead to a special case of population distribution known as seasonal sympatry, in which closely related migrant and resident populations occur in sympatry during winter, but are otherwise allopatric. Residents may initiate breeding prior to the departure of migrants, which could allow interbreeding. Alternatively, early departure of migrants and population differences in reproductive timing may prevent gene flow. Male dark-eyed juncos from seasonally sympatric populations are known to differ in timing of reproductive development as migrants lag behind residents in gonadal growth. Far less is known about female differences in reproductive timing. We caught 18 migrant and 15 resident female juncos early in the breeding season of the resident population (March-April) and collected ovarian tissue to compare expression of genes associated with reproduction using qPCR. We found that residents had significantly larger ovaries than migrants (p <0.001). We further found that resident ovaries may be more sensitive to luteinizing hormone (LH) than migrant females because mRNA transcripts for LH receptor were more abundant in residents (p=0.004). Transcript abundance for other receptors associated with reproduction, however, did not differ between populations. We also asked whether gene expression varied among migrants in relation to their migratory distance as estimated from feather isotope data. We conclude that migrant and resident females differ in timing of reproductive development, that gene expression for receptors associated with reproduction may explain some of the difference, and that reproductive timing in females may serve as an isolating mechanism to prevent interbreeding between resident and migratory populations.
