Pleistocene range expansions promote divergence with gene flow between migratory and sedentary populations of Calothorax hummingbirds

We investigate the influence of postglacial population expansion on genetic structure of reproductively isolated populations that come into secondary contact and produce hybrid zones. We test migratory behaviour to explain geographic patterns of genetic diversity and phylogeographic structure in migratory and sedentary populations of hummingbirds in the Chihuahuan Desert. We assessed genetic structure, demographic expansion and introgression in Calothorax hummingbirds using mitochondrial DNA (mtDNA) and nuclear microsatellites (nSSRs), and ecological niche modelling (ENM) to predict where migratory and sedentary populations resided during Pleistocene climate events. Bayesian analysis yielded three clusters. However, only two clusters match mtDNA haplogroups, one parental in the south (pulcher) and a cluster with two admixed taxa (sedentary and migratory lucifer) that cannot be attributed to any pure parental population. Demographic expansion, gene flow and admixture in the lucifer range...