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

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