Peery, Rhiannon , Raubeson, Linda A. .
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 the disjunct distribution of mesic forest species: ancient vicariance and inland dispersal.Under the ancient vicariance hypothesis, western hemlock populations would have been present in inland regions throughout the Pleistocene.Thus, coastal and inland populations would have been separated for millions of years.Under the inland dispersal hypothesis the inland populations would have gone extinct during the Pleistocene and western hemlock would have survived the glacial period only in refugia along the Pacific Coast. Then, after the glaciers receded, western hemlock would have returned to the inland region via dispersal through one of two routes: the Okanogan or Oregon highlands.To differentiate among these hypotheses we are examining patterns of DNA variation within the chloroplast genome and several different nuclear microsatellite loci.Four non-coding regions of chloroplast DNA (totaling 5,368 nucleotides) have been compared among populations from throughout the range of western hemlock but very little variation was found.Thus, the chloroplast sequence data suggest that the species has gone through several bottlenecks that have eliminated genetic variation within the chloroplast genome.Currently, nuclear microsatellite data are being collected and screened.The microsatellite data should be variable enough to determine the history of western hemlock populations in the northern Rocky Mountains.
1 - Central Washington University, Department of Biological Sciences, MS 7537, Ellensburg, Washington, 98926-7537, USA
Presentation Type: Paper
Location: Peruvian (Cliff Lodge)
Date: Wednesday, August 4th, 2004
Time: 10:15 AM