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

Abstract

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, Ovis dalli dalli, in the Mackenzie Mountains, Northwest Territories, Canada. Parasite diversity included nine species, among which the abomasal nematode Marshallagia marshalli occurred with the highest prevalence and infection intensity. The intensity of M. marshalli 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, Trichuris schumakovitschi, decreased with age. No other parasites were significantly associated with age, body condition, or pregnancy. Our study suggests that M. marshalli might negatively influence fitness of adult female Dall’s sheep.

Parasite intensity drives fetal development and sex allocation in a wild ungulate

“…In our previous study, non-pregnant females from the same group of animals had significantly higher parasite infection intensities and lower body condition than pregnant females 39 . Assuming similar gestation time among fetuses, delayed time of conception can result in births occurring later in the season and, as a consequence, to a variety of post-birth costs for both the newborn and the mother.…”

“…Perhaps supporting a hypothesis of delayed conception, the reduced fetal size in ewes with high parasite intensity may be a consequence of parasite-induced energetic constraints and consequent later conception dates resulting in shorter development time for the fetuses of these highly parasitized mothers 25 , 72 , 73 . In our previous study, non-pregnant females from the same group of animals had significantly higher parasite infection intensities and lower body condition than pregnant females 39 . Assuming similar gestation time among fetuses, delayed time of conception can result in births occurring later in the season and, as a consequence, to a variety of post-birth costs for both the newborn and the mother.…”

“…In this research, we have demonstrated subtle and important mechanisms through which parasites can affect host population dynamics. It is well documented that M. marshalli can negatively impact the fitness of wild and domestic ungulate species 39,90 . Our results suggest that this negative effect also extends to fetal development and fetal sex allocation, via a combination of direct and indirect effects of M. marshalli on the fetus and its mother.…”

“…This work was led by Dr. Norman Simmons with the Canadian Wildlife Service, with the primary objective of doing a demographic study of sheep 38 . The parasite specimens and the associated data collected from these sheep were located in the spring of 2000 at the Canadian Museum of Nature (CMN) in Ottawa (Ontario, Canada) and are permanently archived as “The Simmons Collection” 39 .…”

“…We took advantage of an unprecedented historical collection of parasites and associated data in Dall’s sheep ( Ovis dalli dalli , see Fig. 2 A) collected from the Mackenzie Mountains, Canada in 1971–1972 38 , 39 , to assess the effect of gastrointestinal parasites on fetal development and sex allocation. Dall’s sheep are highly philopatric, females normally remain in the same general area their entire lives, whereas subadult males disperse from their mothers’ group to join bachelor groups 40 .…”