Genetic Diversity, Differentiation, and Inbreeding in Pacific Yew from British Columbia

Abstract

Variation at 21 allozyme loci in Pacific yew (Taxus brevifolia Nutt.) from nine disjunct regions, representing three geographic areas of British Columbia, was measured to estimate the amount and pattern of genetic variability. Pacific yew has moderate levels of genetic diversity compared to that present in associated temperate-zone species, with 1.7 average number of alleles per locus, 42.3% polymorphic loci, and 0.166 mean expected within-region heterozygosity. Among-region genetic differentiation accounted for a significant 8% of the total variation. High gene flow (Nm = 2.99) was observed, and it is argued that the primary cause is seed, rather than pollen, subsequently producing low among-region and high within-region genic differentiation. Wright's gene fixation index, F, averaged 0.472, indicating the presence of high levels of inbreeding. Nel's genetic distances (D) among regions from the same geographic area averaged 0.004, which was significantly lower than the average among regions from different geographic areas (0.021), producing close agreement between genetic relationships and geography. The high levels of inbreeding detected may be attributable to both the ecology and reproductive strategies of the species.