Ecotypic mode of regional differentiation of black cottonwood (Populus trichocarpa) due to restricted gene migration: further evidence from a field test on the northern coast of British Columbia
Abstract:A previous common-garden test located in southern British Columbia revealed that black cottonwood (Populus trichocarpa Torr. & A. Gray) sources from the southern region were distinctly superior in growth and health conditions than their northern counterparts, and restricted gene migration between the two regions was proposed as the main cause of the observed ecotypic mode of regional differentiation. Confirmation of the observed pattern of regional differentiation and the proposed underlying mechanism is very important as it will not only enhance our understanding of the evolution of the species, but also have substantial practical implications. In this study, we examined the performance of 483 clones from 30 populations (drainages) across the entire range in British Columbia in a field trial on the northern coast. Three-year test results confirmed the ecotypic mode of genetic differentiation between the two regions as previously observed in the south, providing further evidence supporting the proposition of restrict gene migration as the underlying mechanism. The southern populations were 87% taller than and twice as healthy as their northern counterparts. Regional differences accounted for most of the detected nonrandom variation, with over 80% in both height and health condition. Of the 30 fastest growing clones that were free of any damages, 27 were from the southern region, whereas only three were from the northern region. Performance was very consistent between sites in the two regions at both population and clonal levels.
Document Type: Research Article
Affiliations: 1: B.C. Ministry of Forests, Lands, and Natural Resource Operations, Tree Improvement Branch, P.O. Box 9518, Stn Prov. Govt, Victoria, BC V8W 9C2, Canada. 2: B.C. Ministry of Forests, Lands, and Natural Resource Operations, Kalamalka Forestry Centre, 3401 Reservoir Road, Vernon, BC V1B 2C7, Canada.
Publication date: February 11, 2012
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