Genetic and morphometric variation in the Holarctic helminth parasite Andrya arctica (Cestoda, Anoplocephalidae) in relation to the divergence of itslemming hosts (Dicrostonyx spp.)

Andrya arctica is a cestode parasite of the family Anoplocephalidae (Cyclop hyllidea), parasitizing lemmings of the genus Dicrostonyx throughout the Ho larctic region. The population structure of this intestinal parasite was st udied from eight different regions, six of which represented different gene tic entities of lemming hosts. Molecular sequence tagged site markers and m inisatellite fingerprints as well as morphology and morphometrics were used to reveal the population structure of A. arctica in the Holarctic region. The results suggest that the evolutionary history of this cestode species h as included different processes acting on different geographical regions. O n the Siberian mainland (host D. torquatus), the division of the parasites into different genetic entities agreed perfectly with the chromosomal races of the lemming hosts that points towards a shared evolutionary history bet ween the host and the parasite ('cospeciation'). The main phylogenetic spli t of Dicrostonyx between Eurasia and North America was not, however, observ ed in A. arctica. This suggests that in the Nearctic (host D. groenlandicus ) the parasite has remained relatively unmodified because of the large cohe sive populations ('coadaptation'). The uniqueness of the Greenland populati on, and possibly also that of the Wrangel Island, can be explained by perip heral isolation, (C) 2001 The Linnean Society of London.