FURTHER PERSPECTIVES ON THE HAIDA GWAII GLACIAL REFUGIUM.

Abstract

Byun et al. (1997) reported molecular evidence supporting a purported, long-term Pleistocene glacial refugium for bears (Ursus americanus) located on or near the Haida Gwaii Archipelago (Queen Charlotte Islands), British Columbia. They examined sequence data from the mitochondrial cytochrome b gene and uncovered two lineages, which differed by an average of 3.6%. The lineages were characterized as (Washington to Haida Gwaii) and (Pennsylvania to central Alaska). The geographically restricted coastal lineage led them to conclude that black bear persisted in the Hecate refugium and during early stages of deglaciation recolonized Haida Gwaii, the coastal mainland, Vancouver Island, and eventually the Olympic Peninsula (Byun et al. 1997, p. 1651). In support of this hypothesis, they cited several lines of evidence for a coastal refugium (summarized in Scudder and Gessler 1989) and other recent molecular studies (Soltis et al. 1991; O'Reilly et al. 1993; Talbot and Shields 1996). Our commentary does not reject the possibility of a Haida Gwaii or Hecate refugium for U. arnericanus, but we argue that the conclusions reached by Byun et al. (1997) may be premature and an artifact of limited sampling of the coastal lineage. Wooding and Ward (1997) also reported two lineages (clade A = continental, lade B = coastal) of U. arnericanus based on sequence and restriction fragment length polymorphism analysis of the mitochondrial control region. When results from both studies are combined with earlier studies (Cronin et al. 1991; Paetkau and Strobeck 1996), widespread north-south distributions for the continental and coastal lineages of U. americanus are observed, including areas of potential secondary contact. We present sequence variation from the mitochondrial cytochrome b gene for the American pine marten (Martes americana) and dusky shrew (Sorex monticolus) that may support an alternative biogeographic hypothesis. These mammals, like U. arnericanus, have extensive distributions (Fig. 1) associated with forested habitats in North America. Our analysis uncovered two distinctive lineages in both species that overlap the coastal and continental lineages of U. arnericanus. In light of phylogeographic work on other codistributed mammals (e.g., Cronin 1992; Hogan et al. 1993; Carr and Hicks 1997; Arbogast 1999), amphibians (Good 1989; Green et al. 1996), birds (Zink 1996), and plants (Soltis et al. 1997),