Speciation, genetic divergence and palaeogeography in the hormogastridae

The genus Hormogaster includes a few species of earthworms, whose disjunct areas of distribution are of great interest. Three of them H. redii, H. pretiosa and H. samnitica-occur in the region of the old granitic shield of Western Europe, and their distribution seems related to some geological events which can be dated with confidence. Sardinian H. pretiosa has a morphology only slightly different from the population found in Northeastern Catalonia and both differ to some extent from that of Roussillon (southwest France). The samples of H. redii are more uniform as also are those of H. samnitica. The electrophoretic analysis of the gene enzyme systems reveals a wide molecular divergence between the Sardinian and both the Pyrenean populations of H. pretiosa, and an unsuspected similar divergence between the latter populations (only 60 km apart): such values suggest splitting of the morphospecies into three sibling species. The more widespread H. redii shows a lesser variability between its populations, even those separated by the sea. The genetic divergence between the populations of Hormogaster is tentatively correlated to geological events. The genetic divergence of the genus Xana from Hormogaster has also been studied.