Friday, August 7, 2009 - 10:50 AM

COS 123-9: Impact of climate change on the development, survival, and overwintering potential of a parasitic nematode of barrenground caribou, Ostertagia gruehneri, on the Canadian tundra

Bryanne M. Hoar, Kathreen Ruckstuhl, and Susan Kutz. University of Calgary


Climate change in the Arctic is occurring at an unprecedented rate and is anticipated to alter the ecology of northern ecosystems, including the patterns, diversity, and transmission of infectious diseases. Ostertagia gruehneri is the most common gastrointestinal nematode in caribou and can cause decreased food intake, weight loss, and reduced pregnancy rates in Rangifer species.  Because O. gruehneri has a direct life-cycle that includes a free-living stage, the development and survival rates of this parasite are influenced by climate and climate change. To investigate the response of the free-living stages of O. gruehneri to climate change, field experiments were done from May to September 2008 and May-July 2009 at the Tundra Ecosystem Research Station (TERS), Daring Lake, Northwest Territories. Fecal plots containing O. gruehneri were established on the tundra under natural and artificially warmed conditions.  Plots were sampled throughout the summer to determine development and survival rates of O. gruehneri and to compare between the two climate regimes (natural vs. warmed).  Effects of both temperature and relative humidity on development and survival were investigated throughout the field season. Three sub-samples per plot were left on the tundra in September 2008 to assess overwinter survival in the spring of 2009.


Results from the 2008 field season suggest development rate of O. gruehneri was not constant throughout the summer and was restricted in both the coldest (early June) and warmest (late July) periods of the season. Survival rates between the two treatments (natural versus warmed) with more infective larvae being recovered from the warmed treatment. In general, larval survival was relatively constant throughout the summer. The highest numbers of larvae were recovered from the plots during mid-July and late August.  Numbers of larvae declined at the end of July and this decline corresponds to the warmest time of year, suggesting that O. gruehneri has an upper tolerance threshold.

Results from the field studies suggest that development and survival of O. gruehneri are constrained by climatic thresholds.  Extreme temperatures (both high and low) affect development rate of O. gruehneri, whereas temperature and relative humidity determine survival rate. Expected increases in temperature and humidity in the Arctic are likely to impact the development, survival, and subsequent transmission dynamics of O. gruehneri. Field results will be used, together with laboratory experiments, to develop and validate conceptual and predictive models for the impacts of climate change on the epidemiology of O. gruehneri.