Effects of specialization on genetic differentiation in sister species of bark beetles

We investigated the relative importance of resource use and geography on ge netic differentiation in the sister-species pair of generalist and speciali st bark beetles: Dendroctonus ponderosae and D. jeffreyi (Coleoptera: Scoly tidae). In two regions, where the distributions of these species overlap, w e collected specimens of the generalist from multiple host species and spec imens of the specialist from its single host species. Using allozyme techni ques, we uncovered genetic differentiation between generalist populations o n different host species in the same region (one locus in each region). How ever, a much stronger pattern of differentiation was found between speciali st populations in the two distantly separated regions (three loci). With mt DNA, we found no significant differentiation between regions in the special ist, or among host species in the generalist, although there was some diffe rentiation between regions in the generalist (AMOVA, P < 0.05). Overall, th e generalist populations maintained approximately 10 times the genetic vari ation in mtDNA as the specialist populations, which suggests that the speci alist either has generally smaller population sizes than the generalist, or has experienced a historical population bottleneck.