Taxonomy, genetic differentiation and Holarctic biogeography of Paranoplocephala spp. (Cestoda : Anoplocephalidae) in collared lemmings (Dicrostonyx;Arvicolinae)

The present study reviews the taxonomy of anoplocephalid cestodes of collar ed lemmings (Dicrostonyx spp.) and describes the patterns of cestode biogeo graphy in the Holarctic region. The morphological differentiation of cestod e species is augmented with a genetic differentiation based on three indepe ndent markers. We show that collared lemmings are parasitized by five host- specific species of Paranoplocephala, three of which are described here as new: P. arctica (Rausch, 1952), P. alternata sp. nov., R serrata Haukisalmi & Henttonen, 2000, P. nordenskioeldi sp. nov. and R krebsi sp. nov. The re description of R arctica shows that the original description of this specie s is composite. Paranoplocephala alternata, P serrata and R nordenskioeldi are shown to have a Holarctic distribution, whereas R arctica and R,krebsi are restricted to the Nearctic region, including Wrangel Island. It is sugg ested that the Holarctic species colonized North America concomitantly with their hosts and that the appearance of the Nearctic species is connected w ith the subsequent divergence of collared lemmings in North America. Geogra phical distribution and sequence data for the first transcribed spacer (ITS 1) of nuclear rDNA show that R alternata and R arctica are sister taxa and that the latter species probably diverged from R alternata in eastern Berin gia. Other phylogenetic relationships among cestode species remained largel y unsettled. (C) 2001 The Linnean Society of London.