Genetic divergence and reproductive isolation between Anisakis brevispiculata and Anisakis physeteris (Nematoda: Anisakidae)s

Abstract

In order to assess the taxonomic status of Anisakis brevispiculata Dollfus, 1966 population samples of this taxon from central and south-eastern Atlantic ocean were compared at 22 enzymatic loci with samples belonging to Anisakis physeteris Baylis, 1923 from the Mediterranean sea and central-eastern Atlantic ocean. Very low interpopulational genetic divergence was observed both within A. brevispiculata (average D Nei=0.008) and within A. physeteris ( D Nei=0.009) despite the geographic distance among the samples, indicating high levels of gene flow in both taxa. On the other hand, the average genetic distance between A. brevispiculata and A. physeteris was found to be D Nei=0.80, a value generally observed between well differentiated congeneric species. The reproductive isolation between A. brevispiculata and A. physeteris is indicated by the following observations: (1) no F 1 hybrids or recombinant genotypes were until now observed; and (2) the two Anisakis species do not seem to share their definitive hosts. The main definitive host of A. brevispiculata is the pygmy sperm whale ( Kogia breviceps), while for A. physeteris it is the sperm whale ( Physeter catodon). Only adult males differ slightly in spicule length, while females and larval stages are not differentiated morphologically. Both A. brevispiculata and A.physeteris show a type II larva. The correct recognition of A. brevispiculata from A. physeteris and from other Anisakis species studied, in either sexes and at any life stage, is made easy by allozyme markers (e.g. Icdh, Gapdh, Sod-1, Np, Aat-2, Adk-2, fEst-2, PepB, PepC-2, Mpi). Diagnostic keys, which can be used for routine identification in the field of these Anisakis worms, based on genetic markers, are given.