Variable rates of random genetic drift in protected populations of English yew: Implications for gene pool conservation

Abstract

Protecting populations in their natural habitat allows for the maintenance of naturally evolved adaptations and ecological relationships. However, the conservation of genetic resources often requires complementary practices like gene banks, translocations or reintroductions. In order to minimize inbreeding depression and maximize the adaptive potential of future populations, populations chosen for ex situ conservation should be selected according to criteria that will result in a reduction of global coancestry in the population. Generally, large populations should reveal lower coancestry and higher genetic variation than small populations. If detailed knowledge about coancestry is lacking, census population number (N c) can be used as a proxy for required characteristics. However, a simple measure of N c may be misleading in particular cases as genetic processes rely on effective population size (N e) rather than N c and these two measures may differ substantially due to demographic processes. We used an example of English yew to address whether N c can be a good predictor of genetic parameters when used in conservation programs. Using microsatellite markers, we estimated allelic richness, inbreeding and coancestry coefficients of six relatively large yew populations in Poland. Each population was characterized by N e using the linkage disequilibrium method. Our results showed that populations of English yew were subject to substantial divergence and genetic drift, with both being inversely proportional to the effective subpopulation size (N e). Additionally, allelic richness appeared proportional to N e but not to N c. However, the N e/N ratio differed greatly among populations, which was possibly due to different population histories. From the results we concluded that choosing source populations based only on their census size can be fairly misleading. Implications for conservation are briefly discussed. © 2012 The Author(s).