Batrachochytrium dendrobatidis survey in Ncandu Nature Reserve and fungal ecology

Abstract

Amphibians across the globe have been experiencing rapid declines, especially in areas with a high amphibian population density. It was assumed that this decline was caused by habitat destruction and climate change. A closer investigation led to the discovery of a parasitic fungus called Batrachochytrium dendrobatidis (Bd), or batrachochytrids as they are collectively known, which is now considered to be the leading cause of amphibian morbidity and mortality. This parasitic fungus causes a disease known as chytridiomycosis, which compromises the osmoregulation and respiratory processes of amphibians. The effect of chytridiomycosis on amphibians' fitness is significant as adults tend to become lethargic as vital metabolic processes that promote optimal organ functions are compromised. Therefore, increasing the risk of predation depending on the degree of infection. This study focused on the amphibian species Amietia delalandii, the common river frog, in the Ncandu Nature Reserve (NNR). The purpose of this study was to determine the presence of Bd in the NNR and, if detected, to determine the distribution and prevalence of Bd. Prevalence was determined by utilizing two isolation approaches on amphibian samples collected at various sites. The purpose of using two different approaches was to determine the isolation success of each approach respectively. Bd was found to be present at the NNR, although some perennial streams and pools tested negative for the presence of Bd. Eleven sampling sites were screened for Bd, with nine being found positive. Therefore, it is clear that the NNR is in a pre-enzootic state, but further monitoring needs to be conducted as it was found that some intermittent pools are positive and are within close proximity to negative sites. Two separate surveys were conducted to determine the seasonal influence on Bd prevalence and found that Bd proliferates more during the summer period having an overall prevalence of 26%. In contrast, the survey conducted in the winter had a 17% overall prevalence. The two sites with the highest prevalence are Steep Glen Kloof and Steep Glen River; these sites are perennial and flow into the lower-lying valley, therefore being a potential cause for the distribution of Bd to downstream localities. Isolation of Bd was done using two approaches: the liquid media approach and the agar approach. Although considerable contamination occurred for both approaches, the agar approach proved to be more successful as contamination of samples could be seen while in the field and could be successfully removed in most instances. The isolation success of the two approaches yielded questionable results as the liquid media approach had an isolation success of 0%, whereas the agar approach had a 72.2% isolation success, making the agar approach more effective. Two in vitro experiments were conducted to determine the effect of a competitor/contaminant on the fitness of Bd. It was discovered that Bd could be significantly

inhibited by a competitor that can secrete inhibitory substances. Therefore, the lack of isolation success for the liquid media approach was caused by the inhibition of Bd by a fungal competitor, complicated by the use of liquid media for attempted isolation of Bd that facilitates the spread of inhibitory substances.