Graduate Thesis Or Dissertation
 

Hidden dynamics : community ecology and costs of parasite infection in African buffalo (Syncerus caffer)

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  • Most wild animals are concurrently infected with multiple parasite species for most of their lives. These parasite species assemble into rich and diverse communities, with parasites using host tissues for growth and reproduction as well as evolving strategies to evade the host immune system. The net effect of these ecological interactions determine disease severity, transmission, host susceptibility, and ultimately host fitness. Traditionally, host fitness and condition have been proposed to structure parasite communities with parasite-parasite interactions playing little to no role. The majority of studies on host-parasite dynamics have been restricted to a few factors, with emphasis on single host-single parasite systems over short periods of time. In order to understand and predict the effects of multiple parasite infection, longitudinal studies coupled with information on whole parasite communities are needed to untangle the effects of parasite-parasite interactions from parasite-host interactions. Therefore, in this thesis, I examine the role of co-infection on parasite community membership as well as the effects of endemic infections on specific measures of host fitness. Specifically, I examine a community of tick bourne hemoparasites (Anaplasma centrale, Anaplasma marginale, Ehrlichia sp. Omatjenne, Theileria parva, Theileria sp sable, Theileria sp. buffalo, Theileria mutans, and Theileria velifera) in a free-ranging population of African buffalo (Syncerus caffer). In chapter two, I examined the dynamics of a rich community of eight hemoparasites of African buffalo (Syncerus caffer) in the Kruger National Park (KNP), South Africa to test the hypothesis that community membership is determined by interactions between hemoparasites. I explored the roles of the parasite community and host genetic factors in driving parasite community membership. I showed that the most important predictors of community membership over a period of four years were infection with parasites using the same host resource. In addition, I observed few interactions among parasites using different host resource during the study period. These results illustrate that the most important predictors of parasite infections are competitive interactions with similar parasites and not host immunity or genetic factors. Then, I investigated the effects that this rich hemoparasite community had on several measures of host health. I used linear mixed models and generalized linear mixed models in conjunction with survival analysis to determine the fitness costs of hemoparasite infection over the study period (Chapter 3). I tested three different groups of host fitness: host fecundity (pregnancy and lactation status), host blood cell parameters (hematocrit, mean corpuscular volume, hemoglobin concentration and total red blood cell count) and measures of host immunity (eosinophil, neutrophil, lymphocyte, white blood cell counts as well as host cytokines). Hemoparasites had almost no effects on host fecundity and immunity and minimal effects on blood cell parameters. In addition, the effects of three hemoparasites on the probability of survival were minimal. Host condition during the dry season in conjunction with the amount of time the host was infected by Anaplasma centrale was associated with a higher probability of survival. Overall, parasite communities in this wild buffalo population are self-regulating and the negative effects of single and aggregated hemoparasites are minimal with host survival being higher for specific parasites. Together these results show how co-infection can contribute to parasite control, host fitness and disease severity
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