Life-history strategies and population dynamics of abomasal nematodes in Svalbard reindeer (Rangifer tarandus platyrhynchus)

The observation that the total abundance of adult nematodes in the abomasum of Svalbard reindeer increases between October and April suggests adaptati on to cope with the Arctic winter. Here we investigate the extent to which selection has led to similar life-history strategies in the 3 most numerous trichostrongyle species. The life-histories are found to differ markedly. We use flexible statistical models for the abundance and dispersion of para sites in the host population. One of the taxa, Marshallagia marshalli, was most abundant and had its highest egg output in the winter. In contrast, th e abundance of the most common taxa, Ostertagia gruehneri, m. gruehneri was stable or declined from autumn to late winter, and the closely related tax a, O. gruehneri, m. arcticus, showed a similar over winter drop. The faecal egg output of these 2 taxa was highest in summer, as found in temperate tr ichostrongyle species. Despite the apparent contamination of summer pasture s with O. gruehneri, calves showed negligible burdens until their second su mmer and the abundance of infection reached an asymptote within their third year. In contrast, the abundance of M. marshalli in calves showed a rapid increase over the first summer and by late winter was similar to peak level s found in adults (8000 worms). This increase could not be accounted for by the developing abomasum larvae population and is therefore evidence for tr ansmission over the winter for this taxa. While M. marshalli showed little between-year variation, O. gruehneri showed 2-fold fluctuation in the abund ance of infection. O. gruehneri may therefore play a role in the fluctuatin g population dynamics of the host. Since there was no apparent decline in a bundance with host age in any of the 3 taxa there was no evidence of reinde er mounting an immune response.