Parallel evolution of an sAat-'hybrizyme' in hybrid zones in Albinaria hippolyti (Boettger).

Populations of the land snail Albinaria hippolyti from Crete were sampled across two hybrid zones separating A. h. aphrodite from A. h. holtzi and A. h. harmonia and studied by means of starch gel electrophoresis. At both sites, frequencies of an otherwise rare allele of sAat reached 0.70 and 0.18, respectively, in the centres of the hybrid zones. It is argued that the allele is deleterious and that it is maintained in the zones by a balance between elevated mutation rates (at least 1.4 times 10-4 and 3.2 times 10-4, respectively) and selection (at least 2 times 10-4 and 1.8 times 10-3, respectively). The observed parallelism may be the result of constraints on the numbers of metabolically active sAat variants possible.