The ecology of chytrid lineages in southern Africa

Abstract

The inter- and intraspecific diversity of microbial communities is known to be an important, but difficult to disentangle, factor in pathogen ecology. Conspecific or interspecific microbial interactions may result in competitive suppression, the evolution of pathogens to greater levels of virulence, environmental niche separation and coexistence or even result in the generation of novel recombinant pathogen genotypes. Batrachochytrium dendrobatidis (Bd), the causative agent of chytridiomycosis, is a uniquely destructive pathogen – it is the proximate driver behind the population declines of an unprecedented number of amphibian species and has undergone a global dispersal. It has also become clear that within Bd are multiple phylogenetically deeply diverged lineages. There is evidence that these lineages vary in ecology and virulence, but diagnostic limitations have hampered research assessing the importance of lineage and lineage interactions on Bd epidemiology. I have developed a novel qPCR-based diagnostic to type the Bd lineage present in amphibian skin swabs, museum specimens and experimental animals quickly and economically, to facilitate the collection of baseline data on chytrid lineage distributions globally and to enable experimental work on lineage interactions and ecology. Using this novel diagnostic assay I have delineated Bd lineage distributions over one of the widest areas to date in South Africa and the Lesotho highlands, where both BdGPL and BdCAPE are shown to coexist, but are associated with different environmental conditions and exhibit distinctly different population structures. The data collected from this fieldwork were used to inform experimental work investigating whether the distributions observed in reality may be due to the lineages exhibiting divergent thermal optima. Finally, I considered the role that the wider fungal community may play in modulating pathogen dynamics by investigating whether a novel Malagasy chytrid may be preventing Bd from establishing on Madagascar, a biodiversity hotspot with a diverse endemic amphibian community.