Dynamics of genetic variation in Taxus baccata: local versus regional perspectives

Abstract

Increasing loss of habitat tends to reduce biodiversity at the inter- and intra-specific levels. Within species, the remaining diversity is often partitioned so that a great amount of neutral genetic variation is assigned to among-population variation. This implies reduced gene flow as a consequence of population isolation. We tested whether random amplified polymorphic DNA (RAPD) markers indicate population and (or) regional differentiation in Swiss populations of English yew (Taxus baccata L.), a dioecious forest tree species with scattered distribution. Our sampling included three northern Swiss regions, each containing four populations, and a central-Alpine region with two populations. Four RAPD primers, giving rise to 41 scorable marker bands, identified all but two sampled individuals as unique genotypes. Analyses of molecular variance (AMOVA) detected no significant differentiation among the three northern Swiss regions yet a marginally significant differentiation of these regions versus the central-Alpine region. Concordantly, Mantel tests revealed isolation by distance only when considering all 14 populations. We postulate that the inferred level of gene flow, through wind-borne pollen and occasional long-distance seed dispersal, prevents isolation by distance in northern Switzerland, where stands of T. baccata are relatively abundant. This perpetuates a coherent regional network of occurrences of T. baccata, as might be expected in a metapopulation.Key words: genetic variation, isolation by distance, metapopulation, population differentiation, RAPD-PCR, Taxus baccata.