Diversity of gastrointestinal helminths in Dall's sheep and the negative association of the abomasal nematode, <i>Marshallagia marshalli</i>, with fitness indicators

<div><p>Gastrointestinal helminths can have a detrimental effect on the fitness of wild ungulates. Arctic and Subarctic ecosystems are ideal for the study of host-parasite interactions due to the comparatively simple ecological interactions and limited confounding factors. We used a unique dataset assembled in the early seventies to study the diversity of gastrointestinal helminths and their effect on fitness indicators of Dall’s sheep, <i>Ovis dalli dalli</i>, in the Mackenzie Mountains, Northwest Territories, Canada. Parasite diversity included nine species, among which the abomasal nematode <i>Marshallagia marshalli</i> occurred with the highest prevalence and infection intensity. The intensity of <i>M</i>. <i>marshalli</i> increased with age and was negatively associated with body condition and pregnancy status in Dall’s sheep across all the analyses performed. The intensity of the intestinal whipworm, <i>Trichuris schumakovitschi</i>, decreased with age. No other parasites were significantly associated with age, body condition, or pregnancy. Our study suggests that <i>M</i>. <i>marshalli</i> might negatively influence fitness of adult female Dall’s sheep.</p>