Patterns and Consequences of Parasitism in North American Red Squirrels (Tamiasciurus hudsonicus)

Date
2014-04-28
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Abstract
Parasites are ubiquitous in nature and, by definition, impose harm on their hosts. The degree of harm is dependent upon many factors, such as co-evolutionary history, host immunity, and the magnitude of infection. Hosts must balance the costs of parasitism with investment in growth, development, and reproduction in order to maximize their fitness. As such, certain host traits may make certain individuals more susceptible to parasitism, which may affect observed patterns and costs of parasitism. For this thesis, I explored the patterns and consequences of parasitism using meta-analytical, experimental, and correlative approaches. Red squirrels (Tamiasciurus hudsonicus) were used to explore hypotheses in a wild host population. I found that several host traits affected patterns of parasitism. Group size scaled positively with parasite infection intensity and prevalence across a wide-breadth of vertebrate species in a meta-analysis, but only for parasites that were contact transmitted. Adult male red squirrels had higher flea infection intensities than females, but only when reproductively active and only as adults. Juveniles at birth had the highest flea intensities than at any other life-history stage. Nematodes had higher egg-shedding intensities in reproductively active hosts than in non-reproductive hosts, possibly owing to a trade-off between reproductive investment and immunity. The costs incurred by hosts appeared to be linked to the patterns of parasitism. For instance, through ectoparasite removal experiments, I found that parasitized juvenile red squirrels were lighter at emergence and less likely to survive from birth to emergence than their treated counterparts. Similarly, treated mothers spent significantly less time grooming than parasitized controls. The intensity of nematode egg shedding, but not flea intensity, was correlated with adult red squirrel body mass, suggesting a possible cost of endoparasitism to host condition. Finally, parasitism varied across time, suggesting that the costs of parasitism may vary seasonally. My results indicate that parasites are distributed heterogeneously amongst their hosts, that parasites can alter the fitness and behaviour of their hosts, and that parasites, ultimately, have the potential to influence host life-histories and demography.
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Keywords
Ecology, Parasitology
Citation
Patterson, J. (2014). Patterns and Consequences of Parasitism in North American Red Squirrels (Tamiasciurus hudsonicus) (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/27274