Evidence for the hypothesis of strain formation in Pomphorhynchus laevis (Acanthocephala): an investigation using mitochondrial DNA sequences.

A hypothesis has been erected stating that in the British Isles the acanthocephalan, Pomphorhynchus laevis can be separated into 3 strains, an English, Irish and marine strain. Ecological and morphological evidence exists in support of this hypothesis. An investigation at the molecular level was conducted in order to test the validity of the existing evidence. A mitochondrial gene, subunit I of cytochrome c oxidase was partially sequenced from 3 Irish populations of P. laevis, 1 Scottish population and 3 English populations. P. laevis sequences from brown trout from Ireland, England and Scotland were very similar, showing a mean sequence divergence of 0.7%. Sequences from two populations of P. laevis from English chub and bullhead were also similar to each other (0.35% divergence). These two groups of sequences, the brown trout group and the chub/bullhead group were 2.2% different. These data confirm the existence of at least 2 strains in Ireland and Britain, although there is evidence to suggest that these strains are defined by their host species rather than by their geographical distributions.