A Comparative Study of Hybrid Zones in the Polytypic Land Snail Albinaria Hippolyti (Gastropoda Pulmonata: Clausiliidae)

Many species of the Mediterranean land snail genus Albinaria are highly polytypic. Because patterns of subspeciation may shed light on mechanisms of speciation in this group, three hybrid zones in A. hippolyti are analyzed. One of these, between the subspecies A. h. aphrodite and A. h. harmonia, was reported on earlier and is included as a reference. The zones were investigated by sampling across them and studying these samples conchologically, anatomically and biochemically. In general terms, the analyses show that all zones are characterised by several to many coincident clines in various types of traits. At each locality, the observed cline widths are of the same order of magnitude. In only one case was a clear association with an environmental transition observed. At all localities, some indication of recombinant disadvantage was found, in the presence of 'hybrizymes', anomalies in the reproductive system, or both. The data, viewed in the light of the snails' distribution and population structure, suggest that the hybrid zones result from secondary contact and are maintained by a balance between dispersal and selection against hybrids. This result supports a model of (sub)speciation in small, isolated populations.

Affiliations: 1: Evolutionary Biology and Systematic Zoology Section, Institute of Evolutionary and Ecological Sciences, University of Leiden, P.O. Box 9516, NL-2300 RA Leiden, The Netherlands