Phylogeographic structure within high-latitude North American birds is likely shaped by a history of isolation in refugia during Pleistocene glaciations. Previous studies of individual species have come to diverse conclusions regarding the number and location of likely refugia, but no studies have explicitly tested for biogeographic concordance in a comparative phylogeographic framework. Here we use a hierarchical approximate Bayesian computation analysis of mitochondrial DNA sequences from 653 individuals of 6 bird species that are currently co-distributed in the boreal forest of North America to test for biogeographic congruence. We find support for congruent phylogeographic patterns across species, with shallow divergence dating to the Holocene within each species. Combining genetic results with paleodistribution modeling, we propose that these species shared a single Pleistocene refugium south of the ice sheets in eastern North America. Additionally, we assess modern geographic genetic structure within species, focusing on Newfoundland and disjunct high-elevation populations at the southern periphery of ranges. We find evidence for a “periphery effect” in some species with significant genetic structure among peripheral populations and between peripheral and central populations. Our results suggest that reduced gene flow among peripheral populations, rather than discordant biogeographic histories, can explain the small differences in genetic structure and levels of genetic diversity among co-distributed boreal forest birds.
LAY SUMMARY
Six currently co-distributed eastern boreal birds share a recent phylogeographic history, expanding from a single common Pleistocene glacial refugia, likely located south of the ice sheets in eastern North America.
This research helps us understand whether species within communities respond in similar ways to large-scale geologic and climatic events.
Differences in genetic diversity among boreal species are most likely due to modern processes such as isolation in peripheral populations, as opposed to discordant histories.
We found significant isolating effects of Newfound and southern periphery populations in Northeastern North America, though this appeared to vary across species.
