Genomic diversity, population structure, and migration following rapid range expansion in the balsam poplar, Populus balsamifera

Rapid range expansions can cause pervasive changes in the genetic diversity and structure of populations. The post-glacial history of the Balsam Poplar, Populus balsamifera, involved the colonization of most of northern North America, an area largely covered by continental ice sheets during the last glacial maximum. To characterize how this expansion shaped genomic diversity within and among populations, we developed 412 SNP markers that we assayed for a range-wide sample of 474 individuals sampled from 34 populations. We complemented the SNP dataset with DNA sequence data from 11 nuclear loci from 94 individuals, and used coalescent analyses to estimate historical population size, demographic growth, and patterns of migration. Bayesian clustering identified three geographically separated demes found in the Northern, Central, and Eastern portions of the species range. These demes varied significantly in nucleotide diversity, the abundance of private polymorphisms, and population substr...