Genetic structure and discordance between genetic markers
Our findings support a correlation between genetic differentiation and landscape features. Whereas our nuclear markers revealed spatial clusters, mtDNA haplotypes exhibited a mosaic distributional pattern. Such mito-nuclear discordance is a common phenomenon in animal studies (Toews & Brelsford, 2012), and various hypotheses and drivers have been proposed this phenomenon, including adaptive introgression, sex-biased asymmetries, incomplete lineage sorting (ILS), and demographic disparities (Bazin, Glémin, & Galtier, 2006; Rheindt & Edwards, 2011; Toews & Brelsford, 2012). In terms of our study species, where females are highly philopatric and less mobile than males (Chen et al., 2016), female-biased dispersal does not explain the observed discordance. Moreover, we did not detect any signal of positive selection, so selection is less likely to be a driver of the patterns we observed. Additionally, the small genetic differences between haplotypes imply relatively recent divergence. Therefore, we propose that the mito-nuclear discordance in our focal species can be attributed to ILS. It is important to note that unpredictable biogeographic patterns derived from mtDNA data is a characteristic feature of ILS, yet all other mechanisms can also result in substantial geographic inconsistencies between mtDNA and nuclear DNA (Funk & Omland, 2003; Toews & Brelsford, 2012).