Discussion
The main goal of this study
was to test competing hypotheses for the location of glacial refugia in
an alpine beetle species, including a hypothesis focusing on the role of
drainage basins as refugia. By focusing on analyses of population
structure and TMRCA estimates from paired populations of the
cold-specialized, riparian beetles in the alpine N. ingenscomplex, we found strong evidence that population structure and patterns
of lineage divergence are correlated with drainage basins in the Sierra
Nevada Mountains, California. This supports the hypothesis that drainage
basins, and by extension microhabitat preferences of a species, allow
for persistence in multiple refugia across the mountain range. We also
provide evidence that post-glacial gene flow can readily obscure the
signature of glacial refugia, if not carefully dissected, and that
episodes of glaciation enhanced lineage diversity in this alpine species
complex through both isolation and hybridization.