PARENT SESSION

Systematics/Zoogeography 4 -- Session Chair: Ronald Van Den Bussche-- Nelson Hall East, Goodwin Forum

GENETIC STRUCTURE AND HISTORICAL BIOGEOGRAPHY OF DISJUNCT AND DECLINING POPULATIONS OF WESTERN GRAY SQUIRRELS IN WASHINGTON. G J. Kenagy¹, Xiaoguang Zheng¹, Brian S. Arbogast¹, Janie Booth¹, Jeff Bradley¹, Mary Linders² and Kenneth Warheit². ¹ Burke Museum and Department of Biology, University of Washington, Seattle, WA, USA; ² Washington Department of Fish & Wildlife, 600 Capitol Way N, Olympia, WA, USA.

ABSTRACT- To investigate the genetic structure and historical biogeography of three isolated populations of western gray squirrels (Sciurus griseus) in Washington State, at the northern geographic limit of this latitudinally wide-ranging species, we sampled 48 individuals from 14 localities within three major population areas in Washington. We sampled an additional 32 individuals from 26 localities across the core of the geographic range to the south, in Oregon and California. We analyzed sequence variation for 377 base pairs of the mitochondrial DNA control region. Our gene tree revealed three significantly distinguishable clades, despite a modest level of differentiation within the species as a whole. Of 20 haplotypes across the entire geographic range, only three were found in the Washington populations, and these were not found outside of Washington. However, the three Washington populations did not nest together in the mitochondrial gene tree but fell instead into two separate clades. The northern populations of this species, in Washington, coincide with northern marginal pockets of oak and pine habitat that represent postglacial habitat recolonizations. The expansion of western gray squirrel populations has apparently been limited by availability of such habitat. The decreased molecular diversity within and among the three Washington populations represents a cause for concern with the conservation status of this species in Washington State. The processes of natural extinction and habitat limitation at the northern margin of the geographic range, combined with anthropogenic habitat destruction represent the conditions that have led to the sensitive status of this species in Washington State.

KEY WORDS: geographic range margin, conservation, historical biogeography, Sciurus griseus