Molecular analysis reveals a cryptic species of Chthamalus (Crustacea: Cirripedia) in the Cape Verde Islands

The intertidal barnacle Chthamalus stellatus has a broad distribution, occurring in the Mediterranean, the east Atlantic shores and east Atlantic Macaronesian Islands (Madeira, the Canaries and the Azores). Traditionally, based on morphological characters, Chthamalus of the Cape Verde Islands were also regarded as C. stellatus. However, using a mitochondrial gene and two nuclear genes, we found that although Chthamalus from Cape Verde is morphologically similar to C. stellatus, there are genetic differences between the two that are larger than those found between different species of Chthamalus. We thus claim that these genetic differences justify the assignment of the Cape Verde populations as an evolutionarily significant unit and a sister clade to C. stellatus. We also show that the connection between taxonomic units that are close to each other lies not only in the resemblance between DNA sequences. We have found that numerous point mutations characterizing the Cape Verde Chthamalus are present as infrequent alleles in C. stellatus, indicating that two close taxonomic units can also share polymorphisms present in their common ancestor.