| Summary: | Data are presented on the genetics and ecology of fish and marine mammal anisakid parasites of the genera Contracaecum, Pseudoterranova and Anisakis from the Antarctic and Arctic-Boreal regions. The three morphospecies C.osculatum, P.decipiens and A.simplex, considered cosmopolitan and euriecious, were each shown by isozyme analysis to include a number of sibling species, differentiated genetically and ecologically. The reproductive isolation of C.raadiatum, an Antarctic species often confused with C.osculatum s.l. was also shown. The C.osculatum-radiatum, P.decipiens and A.simplex complexes achieved a bipolar distribution at different times, from 5-6 to about 1 million years ago, through distinct colonizations of the Antarctic region. The more ancient bipolar distribution (C.radiatum, P.decipiens E) coincides with that of the first colonization of the Antarctic by seals; the more recent one (C.osculatum E) occurred in the Pleistocene. In the three anisakid complexes, Antarctic species show a higher genetic variability than the Boreal ones (average He = 0.21 and 0.14, respectively). This is apparently related to a lower habitat disturbance of the Antarctic region, allowing species to reach higher population sizes, with a lower probability of genetic drift phenomena. In both the Arctic-Boreal and Antarctic regions, differences in host preferences were seen which could be related both to differential host-parasite coadaptation and coevolution and to interspecific competition.
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