| Summary: | To enhance their reproductive success, parasites employ various life history strategies, the two most common being the r and K strategies. R strategists produce many small eggs while K strategists produce a small number of larger eggs (Cavaleiro 2014). Factors that influence differences in life history may be related to differences in environmental temperatures and location (Poulin 2007). While many studies have examined the life history strategies of parasites, few have directly investigated those of the Arctic parasite Marshallagia marshalli. Inhabiting a unique geographical location at subzero temperatures, M. marshalli has been found in the abomasum of many wild ungulates including caribou, reindeer, and muskoxen. However not much is known about the dynamics of transmission. Parasitic invasions and altered transmission are expected to continue under current climate change conditions, potentially resulting in parasite range expansion and disease outbreak (Davidson et al. 2011). Arctic models are appropriate for examining the effects of climate change on parasite distributions and disease transmission as there are fewer confounding variables to consider (Dobson 2009). The purpose of this study is to investigate the life history strategies of M. marshalli and the impact that temperature and latitudinal location impose on them. M. marshalli eggs and larvae were isolated from muskoxen fecal samples from five different latitudinal locations in Canada and the U.S. and measurements for egg length, width, and volume, morula length, width, and volume, and larvae length and width were taken. Measurements were analyzed for significant differences in latitude across the locations and mathematical models were used to predict temperature-dependent impacts on development and mortality times of M. marshalli eggs. We provide evidence that M. marshalli uses both r and K life history strategies depending on the temperature and latitudinal location of their environment, and predicted that increasing temperatures would lead to an increase in egg development time, thereby increasing both the number of parasites present and potentially the risk of infection.
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