Restricted gene flow between two alleged subspecies of Albinaria cretensis (Gastropoda, Pulmonata, Clausiliidae)

Two morphologically similar forms of pulmonate snails of the Albinaria cretensis complex, Albinaria cretensis cf. vexans and Albinaria cretensis sphakiota, with ribbed and relatively smooth shells, respectively, occur sympatrically but with a mosaic distributional pattern in the Imbros gorge (Crete, Greece). These forms were studied conchologically and using allozyme analyses and RAPD to investigate their genetic and phylogenetic relationships. Gene flow between the two forms is minimal. Genetic similarity between morphologically similar forms collected at different places in the gorge is larger than between distinguishable forms found at the same locality. Hybrids are formed only incidentally. There are neither sharp borderlines nor hybrid zones between the two forms. In a gorge c. 10 km to the west, a relatively smooth form is found together with Albinaria cretensis tenuicostata and Albinaria sublamellosa heteroptyx, both characterized by ribbed shells. Using the same methods, it turned out that the form with smooth shells is genetically almost identical to the conchologically indistinguishable one from the Imbros gorge, and different from the local A. cretensis tenuicostata. These data support the view that A. c. sphakiota is a separate species occurring in both gorges. The fact that A. sublamellosa clusters among A. c. sphakiota, does not allow for any conclusions because the analyses were not designed for an investigation including that species. The results are in favour of the view hitherto based on shell morphology mainly, that there are many genetically more or less isolated entities, sometimes with very restricted ranges, within the genus Albinaria.