Gene flow accompanies divergence in Beringian birds

The generation and maintenance of biodiversity are driven by population divergence and speciation. We investigated divergence, gene flow, and speciation in Beringia, a region at the top of the North Pacific Ocean with a history of dramatic landscape alteration through Pleistocene glacial cycles. These cycles repeatedly split and connected the Asian and North American continents, separating and reconnecting avian populations. Glacial refugia within Beringia also isolated some populations for a time before potentially enabling them to reunite during interglacial periods. Prior work suggests gene flow plays an important role in the divergence of Beringian birds. To improve our understanding of the generation of avian diversity in Beringia, we tested models of demographic history in 11 lineages from five avian orders (Anseriformes, Gaviiformes, Charadriiformes, Piciformes, and Passeriformes) using population-, subspecies-, and species-level pairwise comparisons. We sequenced an average of 3,710 ultraconserved element (UCEs) loci from the nuclear genomes of these taxa to examine genetic differentiation and test models of divergence through diffusion analysis for demographic inference (δaδi). All of the inferred best-fit models of divergence included gene flow. Together with prior work, this corroborates that divergence with gene flow is the predominant mode of divergence and speciation in Beringian birds.