Rapid evolution in the Nebria gregaria group (Coleoptera: Carabidae) and the paleogeography of the Queen Charlotte Islands

Morphological differentiation in the ground beetles of the Nebria gregaria group, found on the Queen Charlotte Islands, has been used as support for the glacial refugium proposed for the northwest coast of North America. Two members of this species group, N. charlottae and N. louiseae, are restricted to cobble beaches in this archipelago. A third, N. haida, is found only in alpine regions of the archipelago and the adjacent mainland. The remaining two species of the gregaria group, N. lituyae and N. gregaria, show highly restricted distributions in the mountains of the Alaska panhandle and on the beaches of the Aleutian Islands, respectively. To determine the relationships of the five species, we conducted phylogenetic analyses on nucleotide sequence data obtained from five regions of the mitochondrial DNA. In total, 1835 bp were analyzed. The results suggest that one species, N. lituyae, does not belong in the gregaria group, and that only seven mutations separated the two most divergent of the four remaining species. We also conducted random amplified polymorphic DNA fingerprinting analyses on genomic DNA extracted from the five species. Analyses of genetic diversity revealed a lack of molecular differentiation among the Queen Charlotte species, suggesting that these populations may be postglacial in origin and that together N. gregaria, N. charlottae, N. louiseae, and N. haida might represent local variations of a single species. These results are consistent with conclusions derived for the morphological and genetical differentiation among Gasterosteus populations in the archipelago.