Predictors, Costs, and Consequences of Larval Tapeworm Infection in Geladas (Theropithecus gelada).

Parasitism is integral to primate evolution, contributing to major life history tradeoffs with other processes critical to reproductive success and survival. I investigate how infection with the tapeworm Taenia serialis affects geladas (Theropithecus gelada) in the Simien Mountains National Park, Ethiopia. After identifying T. serialis as the parasite behind the protuberant cysts regularly observed in geladas with the use of molecular tools, I described an overall cyst prevalence of 4.8% in the study population (Chapter 2). To identify infections that do not present as visible cysts, I adapted a non-invasive monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) to detect circulating Taenia spp. antigen in gelada urine (Chapter 4). This assay detected Taenia antigen with high accuracy (98.4% specificity, 98.5% sensitivity, and an AUC (area under the curve) of 0.99). Implementing this assay in the study population, I found that infection is substantially more widespread than would be predicted based on the occurrence of visible T. serialis cysts (16.5% of individuals of unknown status tested positive for antigen presence at least once). Contrary to the female-bias observed in many Taenia-host systems, I found no significant sex bias in either cyst presence or antigen presence. Age, on the other hand, predicted cyst presence (older individuals were more likely to show cysts) but not antigen presence (Chapter 3). This indicates that T. serialis may infect individuals early in life but result in visible disease only later in life. I found that cysts were strongly associated with decreased survival and reproductive success in adult geladas (Chapter 4). Counter to expectations, T. serialis cysts were not strongly associated with decreased fecal testosterone metabolite concentrations (Chapter 5). This suggests that the mechanisms underlying the wild T. serialis-gelada relationship differ from those observed in experimental systems. Together, the analyses contained in this dissertation offer novel insights into the predictors, costs, and consequences of a trophically transmitted larval parasite in wild primates.