We investigated the relative importance of resource use and geography on genetic differentiation in the sister-species pair of generalist and specialist bark beetles: Dendroctonus ponderosae and D. jeffreyi (Coleoptera: Scolytidae). In two regions, where the distributions of these species overlap, we collected specimens of the generalist from multiple host species and specimens of the specialist from its single host species. Using allozyme techniques, we uncovered genetic differentiation between generalist populations on different host species in the same region (one locus in each region). However, a much stronger pattern of differentiation was found between specialist populations in the two distantly separated regions (three loci). With mtDNA, we found no significant differentiation between regions in the specialist, or among host species in the generalist, although there was some differentiation between regions in the generalist (AMOVA, P < 0.05). Overall, the generalist populations maintained approximately 10 times the genetic variation in mtDNA as the specialist populations, which suggests that the specialist either has generally smaller population sizes than the generalist, or has experienced a historical population bottleneck.

We used molecular phylogenetic techniques to study the systematic relationships and host specificity of Psoroptes mange mites, which are pests of numerous domestic and wild ungulates. Phylogenetic analysis of DNA sequence data from the internal transcribed spacer region 1 (ITS1) of nuclear ribosomal DNA indicated that populations of Psoroptes are not host specific. Furthermore, the currently used taxonomy of Psoroptes is not concordant with the phylogeny derived from ITS1. During the course of the study, we discovered apparent paralogous ITS sequences within individual mites as a result of varying polymerase chain reaction reaction conditions. This finding concords with other studies of ITS and suggests a cautious approach when interpreting data from ITS sequences. Host DNA contamination was also found to be a significant problem in data collection, and we report on the development of methods to overcome the problems of contamination in parasitic mites.

In this paper, we provide a molecular phylogeny of the 19 species in the bark beetle genus Dendroctonus. These beetles collectively attack plant species in four different genera of the conifer family Pinaceae. Given substantial variation in diet breadth, in both the types and numbers of plant species utilized, we asked two general questions concerning the evolution of resource use in this group: 1) “How conservative is the evolution of host use in these insects?” and 2) “Does specialization tend to be derived (that is, a “dead-end’’)?”

Ecological explanations for the prevalence of resource specialists are abundant, whereas phylogenetic evidence on their origins is scarce. In this paper, we provide a molecular phylogenetic study of the 19 specialist or generalist species in the bark beetle genus Dendroctonus, which collectively attack species in four different genera in the conifer family Pinaceae. Given substantial variation in diet breadth, we asked two general questions concerning the evolution of resource use in this group. How conservative is the evolution of host use in these insects? Does specialization tend to be derived (i.e., a "dead end")?To answer these questions, we estimated the phylogeny of Dendroctonus using mitochondrial DNA sequences and mapped transitions in resource use on the resulting phylogeny estimate. The evolution of affiliations with Pinus and Picea hosts in Dendroctonus was conservative among beetle species (PTP test; P < 0.012), but there was no significant correspondence between the phylogeny of these beetles and the phylogeny among their Pinaceae hosts (among genera, P = 0.28; among Pinus species, P = 0.82).Degree of specialization, as measured in the proportion of hosts used, was bimodally distributed with "generalist" species utilizing greater than or equal to 60% of the congeneric hosts within their range and six specialist species utilizing less than or equal to 40% of the available hosts. Among the generalists, we found a strong correlation between the number of hosts encountered and the number of hosts utilized (R = 0.97, P < 0.0001), whereas there was no significant correlation among the specialists (R = 0.27, P = 0.59). The evolution of specialization in Dendroctonus proved highly labile-specialists arose from generalists at least six separate times (without reversal) all in derived positions, and closer examination of some specialists revealed instances where they appear to have lost particular host species from their diet. However, evidence from the ecological literature also suggests that several Dendroctonus generalists may have increased their range of host genera within the Pinaceae.