Patterns of amphibian chytrid prevalence and mortality in the Drakensberg Mountains of South Africa and Lesotho

The fungal pathogen of amphibians, (Batrachochytrium dendrobatidis, or Bd) is widespread in southern Africa, yet Bd is not known to have caused population declines and is only rarely associated with amphibian mortality.  Because B. dendrobatidis-associated mortality events are rare in southern Africa, their study may help us identify biotic or abiotic factors that contribute to the negative effects of Bd elsewhere.  For these reasons we have been monitoring amphibian populations in the northern Drakensberg Mountains of South Africa and Lesotho for chytrid  presence and mortality events.  Bd is almost universally present in larval populations of the two most common amphibians in this region, Heleophryne natalensis and Strongylopus hymenopus, and occasional chytrid-associated mortality events of adult S. hymenopus have been observed.  Preliminary surveys show that mean prevalence of Bd infection is high: 68% and 39% of H. natalensis and S. hymenopus tadpoles, respectively.  Bd was present at every site at least once during 2006 and was always present at most sites.  Qualitative evidence suggests that infection prevalence is correlated with season and that high rates of prevalence are associated with mortality events.  Peaks of prevalence and mortality events in S. hymenopus correspond with the warm-wet season, which is also the breeding season for this species.  No mortality events of H. natalensis have been observed.  Monitoring of these populations is continuing and future goals include understanding how biotic factors such as population density and abiotic factors such as spatial context contribute to the distribution and prevalence of Bd.