Historical variation in hatching success in a moving hybrid zone of Carolina and Black-capped chickadees (Poecile carolinensis and P. atricapillus)

FERRETTI VALENTINA; BAINS, ASHVEEN; LEE, RACHEL; CURRY, ROBERT

Vancouver

Congreso; 5th North American Ornithological Conference; 2012

Studies of hybridization in the wild can address some fundamental questions in ecology and evolutionary biology such as the mechanisms of reproductive isolation, and the disruption of local adaptations, among others. Moving hybrid zones, although rare, can provide a temporal window in which to study the dynamics of inter-specific mating and its fitness consequences. Populations impacted by moving hybrid zones will likely suffer changes in fitness over time depending on the position of the interbreeding zone. Here, we study temporal variation in hatching success in the leading and trailing ends of a moving hybrid zone of Carolina and black-capped chickadees (Poecile carolinensis and P. atricapillus). From 2000 to 2011 we monitored nesting activity and hatching success in artificial nests in two study sites located 40 miles apart: Hawk Mountain Sanctuary (HM) and Nolde Forest (NF, both in Berks County, Pennsylvania). At the start of our study NF was located well within the chickadee contact zone, while HM was located north of the leading edge supporting a pure Black-capped chickadee population. Towards the end of our study, however, the leading edge of the contact zone had reached HM, with NF now closer to the trailing edge. We found no differences in hatching success across years within sites; yet, when individual years were used in paired comparisons (i.e., comparisons between the two first and two last years of study), hatching success at HM showed a significant decline, while experiencing a significant increase at NF. Moreover, we found hatching success during the last two years to be significantly higher in NF. Our results provide partial evidence for a hybrid disadvantage. It remains to be tested whether they are a result of an effect of Haldane’s rule in the hybridizing populations.