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The tale of two mice in Northwest temperate rain forests: genetic signature of habitat shifts associated with glacial cycles

Two highly abundant native species of mice inhabit the forests of Washington and nearby parts of the Pacific Northwest. They appear virtually identical, as small brown-gray mice with long tails, but the Deer Mouse (Peromyscus maniculatus) is found over most of the North American continent, whereas Keen’s Mouse (Peromyscus keeni) lives only within the forests of Washington and the nearby Pacific Coast to southeastern Alaska. Burke researchers have investigated the historical background of the local Keen’s Mouse in comparison to the geographically wide-spread distribution of the Deer Mouse by comparing their DNA sequences. Despite their similar physical appearance, the two species show a strong difference in mitochondrial DNA. Graduate student Xiaoguang Zheng was able to calculate migration rates of the genes over the past 2 million years. The two mice have been maintained together as distinct species, with complex and not well understood ecological interactions, during a series of habitat shifts that have occurred in response to climate changes and glaciers that have come and gone from our area about 20 times during this period.

mice in Northwest temperate rain forests
mice in Northwest temperate rain forests
mice in Northwest temperate rain forests


Xiaoguang Zheng was a Burke Museum graduate student and obtained his Ph.D. in Zoology in December 2003. He has returned to China to develop a research program in molecular ecology and biodiversity at the Kunming Institute of Zoology.
Brian Arbogast was a postdoctoral fellow at the Burke Museum and is now an Assistant Professor at Humboldt State University in California.
Jim Kenagy is Curator of Mammals at the Burke Museum and Professor of Zoology in the Biology Department.

X. Zheng, B.S. Arbogast, and G.J. Kenagy. 2003. Historical demography and genetic structure of sister species: deermice (Peromyscus) in the North American temperate rainforest. Molecular Ecology 12:711-724. 

Technical Summary:

To investigate the evolutionary and biogeographical history of Peromyscus keeni and P. maniculatus within the coastal forest ecosystem of the Pacific Northwest of North America, we sampled 128 individuals from 43 localities from southeastern Alaska through Oregon. We analyzed mitochondrial DNA variation using DNA sequence data from the mitochondrial cytochrome-b (cyt-b) gene and control region, and we found two distinct clades consistent with the morphological designation of the two species. The sequence divergence between the two clades was 0.0484 substitutions per site for cyt-b and 0.0396 for the control region, suggesting that divergence of the two clades occurred during the middle to late Pleistocene. We also examined the historical demography of the two clades using stepwise and exponential expansion models, both of which indicated recent rapid population growth. Furthermore, using the program MIGRATE we found evidence of migration from populations north of the Fraser River (British Columbia) to the south in both clades. This study demonstrates the utility of these model-based demographic methods in illuminating the evolutionary and biogeographic history of natural systems.

Peromyscus maniculatus
Peromyscus keeni