Despite introgressive hybridization, North American birches (Betula spp.) maintain strong differentiation at nuclear microsatellite loci

Extensive chloroplast introgression has been documented in polyploid Betula species of eastern North America. However, the extent to which the nuclear genomes of these species are differentiated is unknown. Therefore, we evaluated genetic differentiation among largely sympatric Betula papyrifera, B. alleghaniensis, and B. lenta using nuclear microsatellite markers. Principal components analysis (PCA) and analysis of molecular variation (AMOVA) were used to evaluate genetic differentiation. Bayesian model-based clustering was used to identify putatively admixed individuals. Despite a high incidence of allele sharing, all of the species were significantly differentiated even within zones of sympatry. A number of individuals were identified as possibly admixed between B. papyrifera and B. alleghaniensis and between B. alleghaniensis and B. lenta. Admixture estimates between B. alleghaniensis and B. papyrifera increased significantly moving northward into the sympatric zone, suggesting the ...