Molecular arguments for considering Hysterothylacium fabri (Nematoda: Anisakidae) a complex of sibling species.

The existence of sibling species is widespread among nematodes and the recognition of these has important epidemiological implications. In an attempt to establish whether this is the case for Hysterothylacium fabri, which is present in many Mediterranean fish species, we studied its genetic diversity and analysed its population structure. To do this, we used 266 fourth stage larvae of H. fabricollected from three different host species and used two different methods for characterising genetic variability: isoenzyme electrophoresis and RAPD. The four isoenzyme loci studied are polymorphic, with five or six alleles at each. Significant differences in the deviations from the Hardy-Weinberg law were detected, especially at the PGM locus. A total of 92.1% of the markers revealed by the RAPD technique were polymorphic, demonstrating a great diversity. The UPGMA dendrogram revealed the existence of four genetic groups. Values of Nei's genetic distance, gene flow and the existence of different fixed alleles, together with the deviations from the Hardy-Weinberg law detected in the isoenzyme study, suggest that H. fabri is a complex comprising at least three sibling species with little host specificity, at least in the case of the most abundant species.