Parasite avoidance: the cause of post-calving migrations in Rangifer?

Abstract

Intensities of warble fly larvae, Hypoderma tarandi (L.), were examined in slaughtered reindeer (Rangifer tarandus tarandus L.) from different summer grazing areas of Finnmark County, northern Norway. To test the hypothesis that larval abundance decreases with increase in post-calving migration distance (i.e., distance from calving grounds), herds with differing migration distances were sampled. The prevalence of infection in the total sample of 1168 animals was 99.9%. The study revealed significant differences in larval abundance among herds from different summer grazing areas. Herds with post-calving migrations have significantly lower larval abundances than herds remaining on or near the calving grounds for the whole summer. Between-herds variation in abundance of H. tarandi larvae is assumed to reflect differing densities of the infective stage (adult flies) on the herds' summer ranges. Larval abundance in a herd is in turn negatively correlated with the distance between the main larval shedding areas (i.e., calving grounds) and the areas of greatest transmission (i.e., summer pastures). These results are discussed in relation to transmission of other parasites common to Rangifer and suggest that this host's post-calving migration may be a behavioural adaptation that reduces levels of parasitic infections.

Monarch butterfly migration and parasite transmission in eastern North America

“…Moreover, work on reindeer has shown that warble fly abundance was negatively correlated with the distance between reindeer calving grounds (the main larval shedding area) and summer pastures (Folstad et al 1991, Nilssen andHaugerud 1995).…”

“…Empirical studies indicate that long-distance migrations can reduce parasite prevalence, for example in sea lice infesting Pacific salmon (Krkošek et al 2005(Krkošek et al , 2006, warble flies in reindeer (Folstad et al 1991, Nilssen andHaugerud 1995), and nematodes in fall armyworm moths (Simmons and Rogers 1991). Two mechanisms could cause this association.…”

Ecophysiology of avian migration in the face of current global hazards

“…Conversely, migration may act to reduce infection risk. Empirical studies indicate that the prevalence of particular pathogens or parasite species may be comparatively lower in migratory populations [44,45]. Two complementary explanations for this pattern are that (i) migration allows animals to periodically escape locally contaminated habitats ('migratory escape'); and (ii) long-distance migration weeds out infected animals ('migratory culling') [10,39].…”

A conceptual model for migratory tundra caribou to explain and predict why shifts in spatial fidelity of breeding cows to their calving grounds are infrequent

“…The risk of parasitism may increase as density (gregariousness) on the calving grounds increases. The peri-parturient rise in gastrointestinal nematode egg output caused Folstad et al (1991) to predict that calving grounds "…might develop into transmission foci for parasites, where females and their susceptible calves would experience intense parasitic transmission." As caribou density increases, so does the density of fecal pellets and the risk of exposure to parasites (Folstad et al, 1991).…”

“…The peri-parturient rise in gastrointestinal nematode egg output caused Folstad et al (1991) to predict that calving grounds "…might develop into transmission foci for parasites, where females and their susceptible calves would experience intense parasitic transmission." As caribou density increases, so does the density of fecal pellets and the risk of exposure to parasites (Folstad et al, 1991). This conceptual curvilinear relationship between density (gregariousness) and spatial fidelity on the calving ground approximates a 'flattened inverse U' with a steep portion at extremely high or low densities (Fig.…”