PATTERNS IN CIRCULATION AND TRANSMISSION OF MARINE BIRD PARASITES IN HIGH ARCTIC: A CASE OF ACANTHOCEPHALAN <i>POLYMORPHUS PHIPPSI </i>(PALAEACANTHOCEPHALA, POLYMORPHIDAE)
This study, based on the materials on parasitic infection of marine birds and invertebrates in Frantz Josef Land (FJL) collected in 1991-1993, focussed on the acanthocephalan <i>Polymorphus phippsi</i>. We identified this parasite, confirmed its species status and analysed its circulation and transmission patterns in high Arctic. The causes of its erroneous identification as <i>P. minutus</i> in several studies were also examined. In contrast to <i>P. minutus</i>, the transmission of <i>P. phippsi</i> is realized in marine coastal ecosystems. Its main intermediate host in the Arctic is the amphipod <i>Gammarus (Lagunogammarus) setosus</i>, common in coastal areas of the shelf zone throughout the Arctic basin. <i>P. phippsi</i> population in FJL and the entire European Arctic is on the whole maintained by a single obligate final host, the common eider <i>Somateria mollissima</i>. Prevalence (P) of <i>P. phippsi</i> in this bird reached 100 %, with the maximal infection intensity (IImax) of 1188 and the mean abundance (MA) of 492.1. Other species of birds found to be infected with <i>P. phippsi</i> (Arctic turn, black guillemot, purple sandpiper and several gulls) are facultative and/or eliminative hosts. The most heavily infected birds were Arctic terns (P = 72.7 %, IImax = 227, MA = 47.1), which contained single mature acanthocephalans. For one of the FJL regions, infections flows of <i>P. phippsi</i> through various host categories were calculated. Involvement of birds unrelated to the common eider into the circulation of <i>P. phippsi</i> is facilitated by their feeding character in the Arctic. While coastal crustaceans are abundant, fish food is relatively scarce (polar cod, snailfishes), and so amphipods make up a considerable part of the diet of marine birds in FJL, if not most of it, as for instance in case of Arctic tern. This promotes an easy entry of the larvae of crustaceans-parasitizing helminthes (cestodes and acanthocephalans, including cystacanths <i>P. phippsi</i>) into non-specific hosts and opens broad colonization possibilities. Besides acanthocephalans, the phenomenon of non-specific parasitism has been shown for some cestodes circulating in the Arctic coastal ecosystems. Similar conditions for helminths transmission might have formed in marine coastal refugia during the glacial periods of late Pliocene-Pleistocene. According to the Arctic refugium hypothesis of Hoberg and Adams, this promoted parasitic colonization of phylogenetically distant hosts using similar foraging resources. Thus, present-day transmission patterns of helminthes in high Arctic can be, in a way, considered as a model allowing us to witness various stages of helminthes' speciation by host-switching.