At the European sea shores, subgenus Neritrema (genus Littorina) is represented by two groups of closely related species: “obtusata”: L. obtusata, L. fabalis; and
“saxatilis”: L. saxatilis, L. arcana, L. compressa. Although they are characterized by unique distribution pattern along the intertidal area, they coexist in sympatry,
demonstrate similar morphology and breeding behaviour. This species are low
moving, dioceous and polygamic (females are promiscuous and store sperm of
several males). Some species tend to form ecotypes (e.g. L. saxatilis).
We were interested in barriers maintaining species identity in this system. First, we tested are there interspecies copulation and what are mating preferences? Most males copulated with conspecific females, although mating with heterospecific partners was observed regularly. This focused further study on postcopulatory prezygotic barriers, which still were not studied in Caenogastropoda. Among results of a complex proteomic analysis of male reproductive tissues was the identification of a novel protein with no known domain structure – LOSP. This protein is specifically expressed in the paraspermal cell line and most probably transferred to the female during insemination. The parasperms and their products might contribute to reproductive isolation via involvement in sperm competition. Congruently, LOSP is highly variable between species except L.saxatilis/L.arcana were LOSP most
variable, but species form mixed clusters. LOSP might participate in gametic
isolation and we have confirmed the previous idea that L.saxatilis/L.arcana have not diverged yet and there is strong reinforcement between them.