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

In order to assess the taxonomic status of Anisakis brevispiculata Dollfus, 1966 population samples of this taxon from central and southeastern Atlant ic ocean were compared at 22 enzymatic loci with samples belonging to Anisa kis 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. physete ris (D-Nei = 0.009) despite the geographic distance among the samples, indi cating high levels of gene flow in both taxa. On the other hand, the averag e genetic distance between A. brevispiculata and A. physeter-is was found t o be D-Nei = 0.80, a value generally observed between well differentiated c ongeneric species. The reproductive isolation between A. brevispiculata and A. physeteris is indicated by the following observations: (1) no Fl hybrid s or recombinant genotypes were until now observed; and (2) the two Anisaki s 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 mal es differ slightly in spicule length, while females and larval stages are n ot 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-l, Np, Aat-2, Adk-2, fEst-2, PepB, PepC-2, Mpi). Diagnostic keys, which can b e used for routine identification in the field of these Anisakis worms, bas ed on genetic markers, are given. (C) 2001 Australian Society for Parasitol ogy Inc. Published by Elsevier Science Ltd, All rights reserved.