INSTYTUT DENDROLOGII

Genetic differentiation of natural population of English yew (Taxus baccata L.) in Poland

Taxus baccata L. is a slow-growing evergreen, long-lived, dioecious and wind-pollinated tree with great dispersal capability. Seeds are mainly dispersed by birds and small mammalians. English yew is widely distributed in Europe, but the currently natural range of this species is discontinuous. Populations of yew, in most cases are small and scattered. Taxus baccata is considered as an endangered species and declining in major part of its distribution owing to excessive felling, climate change and lack of natural regeneration associated with browsing game. In many European countries Taxus baccata has been included on the Red List as Vulnerable. English yew is a good example of a species that needs both ex situ and in situ conservation. The 29 forest reserves were established in Poland in order to protect this endangered species. Our results of study will be helpful in an appropriately chosen source of populations.

The main aim of this study was to estimate the levels of genetic diversity and other genetic structure parameters of 31 polish populations of T.baccata, using five nuclear microsatellite markers. What is more, specific objectives were to identify the demographic history in studied populations, which can influence on genetic variation too.

The results of this study indicate that the populations of English yew were found to differ in genetic structure. For example, expected and observed heterozygosity spanned from 44,4% to 83,9% and from 26.2% to 59.3%, respectively. Similarly, allelic richness ranges from 2,4 to 12,5. Moderate level of genetic differentiation was found between studied populations, within an overall Fst=15,5%. This results of Taxus baccata is comparable with those reported for other widespread temperature trees, usually characterized by high level of genetic diversity within populations and low differentiation.

Until now several studies showed that some inbreeding might be present is yew populations and the results of this study with average Fis=9% were close to those reported earlier. This inbreeding is high due to mating between closely related individuals. Generally, the high values of inbreeding are somewhat surprising for long-lived trees in which selfing is prevented by dioecy.

In Poland populations of Taxus baccata get smaller and more isolated. The performed Mantel test indicted a significant correlations between genetic distance and geographic distance. In such populations, genetic drift can have a significant effect on genetic structure. The consequences of long-term effect of genetic drift are loss of variation within populations and increasing genetic differentiation among populations. Moreover, in 13 studied populations, a significant reduction in size, which is call bottleneck, were detected. This process could occur in the past during postglacial recolonization of Taxus baccata from southern refugia towards northern.

In addition, the results have a practical aspects. They have supported program for the protection and restoration ofTaxus baccata in Poland, which have lasted since 2006.