Evolutionary aspects of population structure for molecular and quantitative traits in the freshwater snail Radix balthica


Guillaume Evanno, Department of Ecology and Evolution, Biology Building, University of Lausanne, CH 1015 Lausanne, Switzerland.
Tel.: +41 21 692 42 46; fax: +41 21 692 42 65;
e-mail: guillaume.evanno@unil.ch


Detecting the action of selection in natural populations can be achieved using the QSTFST comparison that relies on the estimation of FST with neutral markers, and QST using quantitative traits potentially under selection. QST higher than FST suggests the action of directional selection and thus potential local adaptation. In this article, we apply the QSTFST comparison to four populations of the hermaphroditic freshwater snail Radix balthica located in a floodplain habitat. In contrast to most studies published so far, we did not detect evidence of directional selection for local optima for any of the traits we measured: QST calculated using three different methods was never higher than FST. A strong inbreeding depression was also detected, indicating that outcrossing is probably predominant over selfing in the studied populations. Our results suggest that in this floodplain habitat, local adaptation of R. balthica populations may be hindered by genetic drift, and possibly altered by uneven gene flow linked to flood frequency.