Population parameters and mito-nuclear mosaicism of Anisakis spp. in the Adriatic Sea.

Recombinant genotypes of A. simplex sensu stricto (s.s.) and A. pegreffii, two species of Anisakis simplex complex found in sympatric waters of the Mediterranean Sea, are believed to be a product of interspecific hybridisation and/or DNA introgression. In contrast, such events within an allopatric area as the Adriatic Sea are unlikely to occur and therefore observed recombination should be assessed more closely. We have genotyped 525 anisakids collected from migratory and non-migratory fish of the southern part of the Adriatic Sea, inferring its omniparentage at nuclear (ITS locus) and matrilineage at mitochondrial locus (cox2). The aim was to address the presence and cause of the recombination within the population and to test its genetic structure under admixture theory. Population parameters, i.e. prevalence, and mean abundance and intensity of anisakids were also evaluated to contribute for future epidemiological risk assessments. As a result, we have inferred the presence of A. pegreffii, A. typica and A. ziphidarum in the Adriatic, lacking type species A. simplex s.s. at both nuclear and mitochondrial locus. A. pegreffii population shows a high level of admixture and heterogeneity and a recent demographic expansion from a small population size. We argue that the observed recombinant genotypes in the Adriatic are a product of ancestral polymorphism and consequent remote genetic introgression.