Population structure was examined using STRUCTURE v2.1 [21,40]. Each STRUCTURE analysis was performed without any prior population assignment and was performed using 10,000 replicates and 5000 burn-in cycles under the admixture model applying the infer α option with a separate α estimated for each population under the F model (where α is the Dirichlet parameter for degree of admixture). Runs were performed under the λ = 1 option where λ parameterizes the allele frequency prior and is based on the Dirichlet distribution of allele frequencies. A uniform prior distribution of allele frequencies over all loci is used when λ = 1. Structured association was performed using the STRAT software [8] that performs association tests with population structure information that is provided by a prior analysis with STRUCTURE [21].
