Strong Differentiation in Mitochondrial Dna of Dendroctonus brevicomis (Coleoptera: Scolytidae) on Different Subspecies of Ponderosa Pine

Abstract

Earlier phylogenetic analysis of the bark beetle genus Dendroctonus based on mitochondrial DNA (mtDNA) uncovered large genetic distances between 2 populations of Dendroctonus brevicomis, 1 in California and 1 in Colorado. The genetic distance between the 2 populations was equivalent to that observed between fully recognized sister species of Dendroctonus and suggested the presence of 2 cryptic species. To test this hypothesis, we sampled D. brevicomis from 12 populations across its range. Using polymerase chain reaction, we amplified a 1,250-bp region of the mtDNA gene cytochrome oxidase I (COX I). A restriction site survey using 8 enzymes revealed 8 fixed differences between western (California, Oregon, Idaho, and British Columbia) and eastern (Colorado, Utah, Arizona, New Mexico) populations, suggesting that D. brevicomis is composed of 2 cryptic species. Moreover, the distribution of these 2 groups corresponds with the distributions of Pinus ponderosa variety scopulorum and variety ponderosa , the principal hosts of D. brevicomis over the majority of its range. We suggest that these populations of D. brevicomis may have become reproductively isolated as a consequence of the geographic separation of the host varieties.