Genetic diversity of sp. A (Nematoda: Anisakidae) parasitizing the European Shag from the Spanish Mediterranean coast.

Sibling species of the (s.l.) complex are habitual endoparasites of cormorants of the Phalacrocoracidae family, worldwide. In Europe, the two species, sp. A and sp. B, have been identified. However, information regarding the occurrence and distribution of these anisakids in cormorants from Spain is scarce. In the present study, 20 specimens of the European Shag, , from the western Mediterranean Spanish marine coast were parasitologically analyzed for the presence of nematodes. All hosts were found parasitized with specimens ( = 1,517). A representative subsample was genetically identified as sp. A by sequence analysis of the mtDNA 2 gene and the ITS1 and ITS2 regions of the rDNA. This represents the first report of sp. A from the Spanish Mediterranean waters. Population genetic analysis was performed including other sp. A specimens from the west Sardinian and the Tyrrhenian Sea. At the intraspecific level, a significant genetic differentiation ( ≈ 0.08, < 0.00001) between the metapopulation from the Spanish Mediterranean coast and that from the Sardinian waters was observed; whereas, no differentiation was found between metapopulations of the parasite from the Spanish and the Tyrrhenian Italian coast. The findings highly support the hypothesis of the adaptation of the life cycle of sp. A in brackish and marine ecosystems. Furthermore, the results on the population genetics of sp. A suggest the possible role of the migration routes of wintering populations of cormorants in the Mediterranean Sea in influencing the parasite genetic structure.