Genome-wide admixture and ecological niche modeling reveal the maintenance of species boundaries despite long history of interspecific gene flow

1.The maintenance of species boundaries despite interspecific gene flow has been a continuous source of interest in evolutionary biology. Many hybridizing species have porous genomes with regions impermeable to introgression, conferring reproductive barriers between species. 2.We used ecological niche modeling to study the glacial and postglacial recolonization patterns between the widely hybridizing spruce species Picea glauca and P. engelmannii in western North America. 3.Genome-wide estimates of admixture based on a panel of 311 candidate gene single nucleotide polymorphisms (SNP) from 290 genes were used to assess levels of admixture and introgression, and to identify loci putatively involved in adaptive differences or reproductive barriers between species. 4.Our paleoclimatic modeling suggests these two closely related species have a long history of hybridization and introgression, dating to at least 21,000 years ago, yet species integrity is maintained by a combination of strong e...