Population ranges of different Littorina species overlap, allowing not species-specific copulations and incomplete reproductive isolation between some of them. This poses question how these coexisting related species maintain their identity. Gamete incompatibility is one of the possible mechanisms of
reproductive isolation in such system. In this case, a search for acrosomal
proteins that are responsible for the specificity of fertilization can be a promising direction. In some taxa (e.g. abalones and sea urchins) species-specific acrosomal proteins were studied. Mutations in these proteins are supposed to cause speciation in these groups. Thus, the search for acrosomal proteins advances our understanding of the reproductive isolation mechanisms and speciation in genus Littorina. For present study we obtained reproductive tissue extracts, total lysates of different body parts and phenolic fixations for 5 periwinkle species (L.obtusata, L.littorea, L.saxatilis, L.arcana, L.compressa), and acrosomal extract only for L.obtusata. The protein samples were analyzed using proteomics methods (1D and 2D-electrophoresis and «bottom up» analysis). We were able to identify a sperm-specific protein of L.obtusata with an approximate
weight of 17 kDa. Edman sequencing allowed identifying its first 10 amino acids. Based on this sequence we made degenerate primers and used them for 3'-RACE. Finally, we identified a reproductive-specific transcript of the target protein that shows no homology with any known proteins. This protein is a species-specific marker of L.obtusata. Its acrosomal localization and
involvement into reproductive isolation process need further examination