Evidence for low genetic diversity and metapopulation structure in Canada yew (Taxus canadensis): considerations for conservation

Canada yew (Taxus canadensis Marsh.) is a gymnosperm that grows in the unde rstory of mixed and deciduous forests of northeastern North America. This s hrub had no economic importance until the discovery of paclitaxel, or TAXOL (R), which is a compound found in plant tissue and used in cancer treatmen t. With the intensifying harvesting pressure on natural populations of this species, the natural gene pool might be affected. The objective of this st udy was to estimate the levels of genetic diversity and population structur e in Canada yew, before any sizeable effects resulting from harvesting appe ar. Six natural populations of Canada yew were sampled in Quebec. Genetic d iversity was estimated at 22 loci coding for 12 enzyme systems. At the popu lation level, the number of alleles per locus was 1.32, the percentage of p olymorphic loci was 26.5%, and the observed heterozygosity was 0.102. These results show that Canada yew is genetically less diverse than other yew sp ecies and the great majority of gymnosperms. However, the amount of populat ion differentiation was substantially higher (F-ST = 10.2%) than that for o ther conifer and tree species growing in the boreal-temperate zone. Hypothe ses related to the biogeography of the species and a likely metapopulation structure are proposed to explain the observed trends.