Disease dynamics in a metapopulation of Amietia hymenopus

Abstract

Batrachochytrium dendrobatidis (Bd), a fungal pathogen of amphibians capable of adversely affecting all levels of organisation up to community level. In South Africa B. dendrobatidis is widely distributed including in the Drakensberg Mountains where it infects Phofung river frogs, Amietia hymenopus. Our objective was to identify factors driving disease dynamics of B. dendrobatidis in A. hymenopus. We made use of a 10 year data set that resulted from monitoring this host-pathogen relationship in tadpoles from the Mont-aux-Sources region. Tadpoles were collected twice annually from four rivers: Vemvane, Tugela, Bilanjil and Ribbon Falls. Presence/absence of B. dendrobatidis was determined through qPCR analysis and cytological screening of tadpole mouthparts. We found no statistical significant difference between the sites, but infection was more consistent between years at sites situated along popular tourist hiking trails. Interestingly, infection prevalence, although higher in summer, did not differ significantly between seasons. High altitude coincides with moderate temperatures resulting in a repressed fluctuation on the pathogen's prevalence between warmer and colder months. Rainfall, however was negatively correlated with infection prevalence. Growth rate ratios of tadpoles indicated that tadpole size and not developmental stage is one of the main drivers of infection. Persistently low to moderate infection prevalence and low pathogen virulence implies that B. dendrobatidis acts as an endemic infection in A. hymenopus. Furthermore microsatellites were developed for this species during this study to aid in population genetics, unfortunately this was not possible, but it will be very useful for future conservation