Insights into the Migration Routes and Historical Dispersion of Species Surviving the Messinian Crisis: The Case of Patella ulyssiponensis and Epizoic Rhodolith Lithophyllum hibernicum

The genus Patella (Patellogastropoda, Mollusca) is represented by a group of species exclusive to the Northeast Atlantic Ocean (including Macaronesian archipelagos) and Mediterranean Sea. The species Patella ulyssiponensis and Patella aspera are common in European waters, with the first inhabiting continental coast, and the second endemic to Macaronesian archipelagos. However, the acceptance of these two lineages as separate species is still highly debated. The red coralline species algae Lithophyllum hibernicum, distributed from Northeast Atlantic to the Mediterranean, is usually found as epilithic crusts or unattached forms (named rhodolith beds), although it also forms epizoic crusts on other organisms, e.g., shell surfaces. In order to study the historic dispersal and migration routes of the Patella ulyssiponensis-aspera complex, taxonomic, genetic and biogeographic approaches were employed based on haplotype network analyses and estimations for the most common recent ancestor (TMRCA), using Cytochrome Oxydase I. A synonymy for these two species is proposed, with the presence of a shared haplotype between the continental (P. ulyssiponensis) and insular (P. aspera) lineages, and with basis of morphological and nomenclatural data. We propose an evolutionary scenario for its dispersal based on a high haplotype diversity for the Mediterranean regions, indicating its possible survival during the Messinian Salinity Crisis (6–5.3 Mya), followed by a colonization of the Proto-Macaronesian archipelagos. The epizoic association of L. hibernicum on P. ulyssiponensis shell adult surface is recorded in this study, likewise the promotion of settlement conditions provided by these coralline algae to P. ulyssiponensis larvae, may explain the reach of P. ulyssiponensis distribution through rhodolith transportation.