Glacial refugia: sanctuaries for allelic richness, but not for gene diversity

Glacial refugia are generally expected to harbor higher levels of genetic d iversity than are areas that have been colonized after the retreat of the c olonization often involves only a few individuals. A new paper by Comps et al. challenges this expectation by demonstrating a more complex situation i n the European beech Fagus sylvatica, for which some measures of genetic di versity are higher in newly colonized areas than in refugia. The key to und erstanding this counter-intuitive result rests both in the estimators used to measure genetic diversity and in the processes affecting these estimator s during postglacial recolonization.