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).