Ancestry informative markers were employed to test for population stratification using the STRUCTURE v2.2 software (Pritchard et al., 2000). This software places individuals in K clusters of potential putative populations separated by marker frequencies. A no-admixture ancestry model with K set to 1 was initially used to infer the Dirichlet parameter lambda of the distribution of allele frequencies. The value of lambda thus obtained was later used under an admixture model with allele frequencies correlated using a burn-in length of 50,000 followed by 50,000 Markov Chain Monte Carlo iterations which was sufficient to yield stable results.
