Differences in allele frequencies of<i>Aat</i>between high- and mid-rocky shore populations of<i>Littorina saxatilis</i>(Olivi) suggest selection in this enzyme locus

Abstract

Summary Samples of the intertidal prosobranch Littorina saxatilis were collected along vertical transects from high- to mid-store levels at five different geographic locations of western Europe. Electrophoretic screening of ten metabolic enzymes revealed five highly polymorphic loci. Four of these showed no or few significant differences in allele frequencies between high- and mid-shore samples of Littorina saxatilis . The fifth locus, Aat (aspartate aminotransferase, EC 2.6.1.1), showed clinal variation in allele frequencies over the few metres of each transect, suggesting that this locus, or a coupled locus, is under selection with a slow allele ( Aat 100 ) favoured in mid-shore habitats and a faster allele ( Aat 120 ) selected for in the high littoral fringe.