The environmental changes trailing the continuous warming of the Arctic is affecting all trophic levels of the ecosystem and has widespread consequences for animal populations. The muskox (Ovibos moschatus) is the largest Arctic herbivore, and it is highly specialised to withstand this very seasonal and extreme Arctic environment. The expected temperature increase may in time exceed the thermal tolerance of the muskox making it more susceptible to infections. Pathogen diversity and intensity will likely change as a result of the altered environmental conditions, which, along with anthropogenic activity, add additional external stressors to the already challenged muskox.
The muskox is native to North-East Greenland, but translocations to the west coast have expanded its current distribution to include multiple areas from the High-Arctic to the Subarctic. In the face of the current climate change, the wish to translocate more muskox populations within Greenland, and the unknown population trends, we need baseline knowledge of the current diversity and abundance of micro- and macroorganisms in the Greenland muskox populations.
The main aim of my PhD project was to elucidate the present variation in endoparasitic and gut bacterial diversity among different Greenland muskox populations and to provide baseline knowledge on the prevalence of selected zoonotic pathogens within Greenland muskoxen and sheep (Ovis aries). To meet this aim, I collected faecal samples from three different muskox populations in Greenland: Zackenberg in High-Arctic North-East Greenland, Kangerlussuaq in Low-Arctic central West, and Ivittuut in Low/Subarctic South-West Greenland. Samples from domestic sheep in South Greenland were also included. Furthermore, I collected serological samples from the Kangerlussuaq and Ivittuut muskox populations, and domestic sheep.
For the first paper (I), I applied serological methods to screen muskox and sheep samples for antibodies against the protozoan parasite Toxoplasma gondii and the bacterium Erysipelothrix rhusiopathiae, as these pathogens are zoonotic and have potential population effects. Furthermore, faecal samples from all muskox populations and sheep were examined by real-time PCR for specific DNA from the potentially zoonotic parasites Giardia duodenalis and Cryptosporidium. Subsequently, one G. duodenalis positive sample and two Cryptosporidium positive samples were successfully genotyped to evaluate their zoonotic importance. The results revealed the first finding of Toxoplasma and Erysipelothrix seropositive terrestrial mammals in Greenland and the first detection of the zoonotic parasite species G. duodenalis assemblage A and C. parvum in Greenland non-human mammals. The overall estimated prevalence of the selected zoonotic pathogens was relatively low, suggesting that the population health impact is currently not a concern, while the relevance to public health remains unknown.
Paper II investigated the faecal bacterial microbiota of wild muskoxen and compared diversity measures and bacterial abundances among populations. Furthermore, I included samples from sheep and captive muskoxen from the Copenhagen Zoo, Denmark, for comparison. Findings suggested a geographical variation in faecal bacterial diversity and composition in wild Greenland muskoxen, with a higher diversity in North-East Greenland than in West Greenland populations. The gut microbiota of Greenland muskoxen appeared to be more similar to sheep than to captive muskoxen, suggesting that environmental factors may play a major role in the composition of the bacterial gut microbiota. The effects of the observed differences on the health of the animals remain uncertain but the findings suggest that the bacterial gut microbiome of the muskox is plastic and is affected by external conditions.
In paper III faecal samples from all three muskox populations and sheep were examined for parasite eggs/oocysts and infection intensities were quantified by faecal egg count. Furthermore, metabarcoding of DNA extracted from faecal samples was used to further elucidate parasite diversity and prevalence in the case of species with intrinsic or seasonal low egg excretion, e.g., Teladorsagia boreoarcticus (Nematoda: Ostertagiinae) is not expected excrete eggs during
winter. Some spatial difference was observed, with a higher parasite diversity in southern Greenland and sheep. Furthermore, the nematode genus Trichuris was detected in South-West Greenland muskoxen (by metabarcoding only) and in sheep (by metabarcoding and microscopy), but not in any of the other muskox populations. This suggests a potential spill-over from sheep to muskoxen, though the transmission route is unknown, as the two species are not believed to be sympatric. The intensity of the parasite infections appeared to depend on the age of the host and the season of sampling. In general, the infection intensity or prevalence did not differ among adult muskoxen from the three populations, despite the climatic differences. However, the cestode genus Moniezia was more prevalent and had a higher infection intensity in muskoxen
from Kangerlussuaq in central West Greenland, tentatively due to drier and more suitable conditions for the mite intermediate host. Overall, the findings of this project expand our knowledge of the diversity and prevalence of parasites and zoonotic pathogens in Greenland muskoxen and domestic sheep and provide new insights into the factors that drive the diversity of the bacterial gut microbiota of wildlife hosts. These results may provide useful information for future research wishing to monitor Greenland wildlife populations, further investigate the transmission routes of pathogens between people, wildlife, and domestic animals, or seeking to explore the correlations between environmental
conditions and gut microbiota, or the possibilities of using microbiomes in the management of animal populations.