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Abstract
Many factors influence rates of parasitic infection in host populations. Among these factors host behavior and physiology are of primary importance. Host behavior influences parasite transmission by modulating the contact rate between hosts and parasites. Social behaviors can increase host exposure to parasites by bringing susceptible hosts into close contact with infected individuals, while antiparasite behaviors specifically reduce host exposure to parasites. After exposure, physiological factors such as host nutrition, determine whether parasites can successfully establish themselves, survive and reproduce within the host. In this study, I investigated the links between social behavior, antiparasite behavior and gastrointestinal parasitism in African bovids and I also looked at the effects of host nutrition on the response to infection.
Two components of bovid social organization increased rates of parasite transmission across hosts. First, species living in groups had higher parasite prevalence than solitary species. Furthermore, within group living hosts, parasite prevalence increased with increasing group size in cases where the parasite was host-specific, and the observed group size accurately reflected intra-specific contact rates. Parasite prevalence was also higher in species that inhabit defined territories compared to free-roaming species. Within populations, highly territorial individuals had higher infection intensities than less territorial individuals. Finally, per capita parasite richness was highest in individuals from host species that both live in groups and defend territories.
Species with high risks of acquiring infections may use antiparasite behaviors to reduce potentially high rates of parasite transmission. I looked at the use of selective feeding and selective defecation behaviors as potential antiparasite strategies in bovids. Selective defecation (dung localization) behavior was positively correlated with nematode prevalence suggesting that this behavior actually increased parasite transmission. On the other hand, fecal avoidance during feeding (selective feeding) may in fact reduce host exposure to fecally-transmitted parasites. In this study, fecal avoidance was experimentally demonstrated in one host species, and a simple model based on field data predicts that rates of selective feeding in hosts will vary depending on factors such as season and host nutritional status. Nutrition was also an important predictor of host infection rates. Under stressful drought conditions, species and individuals with poor diets were less able to manage their parasite infections, suggesting that nutrition affects the host's response to infection.
In conclusion, this thesis demonstrates that social species are subject to high rates of parasitism as a result of grouping and territorial behaviors. In addition, hosts with high infection risks may respond to this increased vulnerability to parasites by using selective feeding as an antiparasite strategy. After a host has been exposed to a parasite, physiological factors, like nutrition, will determine the outcome of the host/parasite interaction. In cases where the host is nutritionally deficient, parasites can have significant negative effects on the host, potentially leading to population level ramifications.
