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Systematics Section / ASPT

Peery, Rhiannon [1], Raubeson, Linda A. [1].

Postglacial recolonization of western hemlock (Tsuga heterophylla [Raf.] Sarg.).

After the last glacial period, western hemlock recolonized its current range from refugia. Disjunct populations of some otherwise coastal mesic forest plants, such as western hemlock, are found inland in the northern Rocky Mountains. Two contrasting hypotheses have been proposed to explain these disjunct distributions of mesic forest species: vicariance and inland dispersal. Under the vicariance hypothesis, western hemlock populations remained in inland regions during recent Pleistocene glaciations. Thus, coastal and inland populations would have been separated for many thousands of years. Under the inland dispersal hypothesis the inland populations would have gone extinct during the Pleistocene and western hemlock would have survived the most recent glacial period only along the Pacific Coast. Then, after the glaciers receded western hemlock would have returned to the inland regions via dispersal. To differentiate between these two hypotheses for western hemlock, we are examining patterns of nucleotide variation within the chloroplast genome. Four non-coding regions of chloroplast DNA have been compared among populations from throughout the range of western hemlock but little variation has been found. Areas of increased genetic variation should indicate locations of refugia. Western hemlock populations in Queen Charlotte Island, southern Cascades of Oregon, and inland areas of Montana show modestly-increased amounts of sequence diversity, suggesting that the vicariance hypothesis may best explain western hemlock recolonization. However, coalescence calculations, based on our sequence data and estimating the time to the MRCA (most recent common ancestor), do not allow us to reject the inland dispersal hypothesis.

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1 - Central Washington State University, Department of Biological Sciences, Ellensburg, Washington, 98926-7537, USA

postglacial recolonization
Tsuga heterophylla

Presentation Type: Oral Paper
Session: 25-3
Location: 410/Hilton
Date: Tuesday, August 16th, 2005
Time: 8:30 AM
Abstract ID:237

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