[Pre-print] Spatial and temporal assessments of genetic structure in an endangered Garry oak ecosystem on Vancouver Island

Abstract

Garry oak (Quercus garryana Dougl. ex Hook.) is a deciduous tree whose ecosystem is listed “at-risk” throughout its range in British Columbia (B.C.), Canada, under the Canadian Species at Risk Act (SARA). Garry oak ecosystems host the most diverse flora for coastal B.C. yet they account for less than 0.3% of the province’s landbase. Due to the loss and degradation of Garry oak habitat, many associated plant and animal species that rely on these sensitive ecosystems are endangered. Microsatellite markers were used to investigate temporal changes in fine-scale population genetic structure of 121 Garry oak trees from the Nanaimo region (Vancouver Island, B.C.) using diameter at breast height as a proxy for age. Overall, allelic diversity was moderate, ranging from 3.0 to 7.5 alleles per locus with an average of 4.4 (± 0.4 SE) across all loci. Global FST of 0.06 and 0.09 suggests significant departures from Hardy-Weinberg equilibrium among all populations and age-classified subpopulations, respectively. We found no evidence for change in genetic diversity across generations. Our results indicate low levels of differentiation within populations and high levels of gene flow among populations, suggesting an adaptive potential for Garry oaks in response to future climate change events.