Structure of Anisakis simplex s.l. populations in a region sympatric for A. pegreffii and A. simplex s.s. Absence of reproductive isolation between both species.

The aim of this study was to determine the genetic structure of A. simplex s.l. populations. This was done by applying PCR-RFLP and RAPD-PCR to 42 specimens morphologically identified as third stage larvae of A. simplex s.l. Of these larvae, 59.26% of those of Mediterranean origin are identified by PCR-RFLP as A. pegreffii. In Atlantic waters, this percentage dropped to 20.00% while A. simplex s.s. represents 66.67%. However, findings seem to suggest that the taxonomic status of both species should be reconsidered owing to: (i) the high gene flow value that we detected between A. simplex s.s. and A. pegreffii; (ii) the short genetic distance between both members of the A. simplex complex; (iii) the fact that hybrid genotypes represent 16.67% of the parasites analyzed and are represented in all the populations studied, except for the Cantabrian one. When the genetic variation is estimated between the 42 individual A. simplex s.l. specimens studied these can be classified into four groups. The genetic distances and gene flow between three of them are compatible with the existence of three different genetic populations. The fourth is comprised of a single specimen of L3, identified both by PCR-RFLP and by RAPD-PCR as a new genotype.