Abstract:
The genetic impact of barriers and Pleistocene glaciations on high latitude resident species has not been widely
investigated. The Clark’s nutcracker is an endemic North American corvid closely associated with Pinus-dominated
forests. The nutcracker’s encompasses known barriers to dispersal for other species, and glaciated and unglaciated
areas. Clark’s nutcrackers also irruptively disperse long distances in search of pine seed crops, creating the potential
for gene flow among populations. Using the highly variable mitochondrial DNA control region, seven microsatellite
loci, and species distribution modeling, we examined the effects of glaciations and dispersal barriers on population
genetic patterns and population structure of nutcrackers. We sequenced 900 bp of mitochondrial control region for
169 individuals from 15 populations and analysed seven polymorphic microsatellite loci for 13 populations across the
Clark’s nutcracker range. We used species distribution modeling and a range of phylogeographic analyses to
examine evolutionary history. Clark’s nutcracker populations are not highly differentiated throughout their range,
suggesting high levels of gene flow among populations, though we did find some evidence of isolation by distance
and peripheral isolation. Our analyses suggested expansion from a single refugium after the last glacial maximum,
but patterns of genetic diversity and paleodistribution modeling of suitable habitat were inconclusive as to the location
of this refugium. Potential barriers to dispersal (e.g. mountain ranges) do not appear to restrict gene flow in Clark’s
nutcracker, and postglacial expansion likely occurred quickly from a single refugium located south of the ice sheets.