Patterns of helminth and protozoan parasite infections in bighorn sheep, Ovis canadensis: sex, season and activity
Date
2020-01-07
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Abstract
Males and females in sexually dimorphic species show differences in their physiology and behavior. Each sex may invest energy in mating and reproduction, rather than immune function at different times of the year since they have different priorities, i.e., securing mating access vs increasing reproductive events. This means that the two sexes may be more susceptible/ less tolerant to parasites at different times of the year. Since this is an observational study, I will be using fecal egg counts (FEC) in terms of eggs per 4 grams (EP4G) as a proxy for susceptibility/tolerance. Furthermore, when individuals have higher parasite FEC, they may need to spend more time grazing and ruminating to ensure enough energy to be able to invest in immune function. That is, higher FEC may lead to individuals spending more time grazing and ruminating as parasites might be siphoning energy and nutrients away from the hosts. I used bighorn sheep, Ovis canadensis, and five of their natural parasites, strongyle, Nematodirus spp., Marshallagia spp., lungworm and Eimeria spp., to investigate seasonality of parasites and host-sex bias and whether higher parasite FEC leads to individuals spending more time grazing. Generalised linear mixed models suggest that parasite FECs are different for male and female bighorn sheep between winter and non-winter seasons. However, the pattern of FECs between the sexes differ based on the parasite group. Strongyle FEC was significantly higher for both sexes during non-winter with male counts being higher than female counts in both seasons. Eimeria spp. count was higher in females compared to males compared in both seasons, but non-winter counts were higher than winter counts. In contrast, FECs for Marshallagia spp., and Nematodirus spp. was significantly higher in females in non-winter, but significantly higher for males in winter months. Following a similar pattern, lungworm larva counts were higher for males during winter, while female counts were lower in winter. Additionally, linear mixed models suggest that bighorn sheep individuals with higher strongyle FEC trended to increase the percent of time that individuals spent grazing, while higher Marshallagia spp. FEC showed a trend in decreasing the percent of time that individuals spent grazing. However, FECs did not affect the time individuals spent ruminating or laying.
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Keywords
bighorn sheep, helminth parasite, protozoan parasite
Citation
Rijal, S. (2020). Patterns of helminth and protozoan parasite infections in bighorn sheep, Ovis canadensis: sex, season and activity (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.