The genetic isolation between some populations of Proasellus coxalis

We tested the reroductive compatibility existing between four geographically different populations of Proaselis coxalis (Crustacea Isopoda) collected in the river Sarno (near Naples) and on three Sicilian sites: San Domenico; Villa Grazia di Carini and Enna. By means of laboratory hybridization experiments (“no-choice” method) we investigated and characterized the reproductive isolation established between these populations under allopatric conditions. The populations San Domenico and Enna are reproductively isolated from Villa Grazia di Carini and Sarno, so that they may be considered as belonging to different species. The mechanism of reproductive isolation are of postzygotic nature only: embronic death, hbrid inviability and sterility of the surviving hybrids. These results agree with tie theory of aioatric speciation, according to which in the first phase of speciation only post-zygotic mechanisms occur as an accidental product of genetic divergence.