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

Abstract

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 occurrence of hybridization in previously glaciated habitats. In contrast, admixture proportions of B. papyrifera and B. alleghaniensis did not show a significant geographic trend, which points to recent ancestry as the likely cause of allele sharing between these two species. We suggest that allele sharing of B. papyrifera and B. alleghaniensis results from a combination of ongoing gene flow and historic introgression via pollen swamping during northward colonization into postglacial environments.

How Many Tree Species of Birch Are in Alaska? Implications for Wetland Designations

“…kenaika having a diploid genetic pattern, possibly a function of being a balanced allotetraploid, whereas the patterns in B. papyrifera are consistent with chromosome counts indicating that it is a pentaploid (Furlow, 1997). The general difference of samples from Alaska and Alberta (Western group) from the Eastern samples is consistent with the patterns detected by Thomson et al (2015), who observed distinct chloroplast haplotypes in western Canada, in addition to some samples that had haplotypes more common in eastern North America. We find two aspects of these results especially intriguing.…”

“…However, at the species level, hybridization and introgression appears to be a common thread (Wang et al, 2013(Wang et al, , 2016Zohren et al, 2016;Tsuda et al, 2017). One study, using microsatellite data (Thomson et al, 2015), focused on North American Betula, finding distinct geographic groupings and a signature of recent introgression. However, as far as we are aware, wide sampling from Alaska has not been included in any genetic based study of Betula.…”

Unidirectional diploid–tetraploid introgression among British birch trees with shifting ranges shown by restriction site‐associated markers

“…The genus Betula (birches) comprises about 60 species of trees and shrubs, among which polyploids are common (Ashburner & McAllister 2013;Wang et al 2016) and hybridization is frequent (e.g. Ashburner & McAllister 2013;Thomson et al 2015;Wang et al 2014b;Palm e et al 2004;Anamthawat-J onsson & T omasson 1990;Anamthawat-J onsson & Th orsson 2003;Anamthawat-J onsson et al 2010). The genus is widespread in the Northern Hemisphere with species ranging from north of the Arctic Circle (B. nana) to the subtropics (B. alnoides).…”

Multiplex and characterization of new EST-derived microsatellite and transferability among five Eucalyptus species (Myrtaceae)

“…These markers were classified as transferable because there was amplification and polymorphism in all species and the hybrid tested. Loci with high transferability between various species are useful genetic markers for interspecific research on topics such as speciation and hybridization (THOMSON et al, 2015). Aside from two markers that were already described by other studies, the loci EUCeSSR479 were only tested for E. urophylla and E. tereticornis and EMBRA1732 only for E. grandis and E. globulus, demonstrating herein that they can be used at least in other two species (E. saligna and E. brassiana) and a hybrid (E. grandis x E. urophylla) ( Table 2).…”