Rapid Evolution of Adaptive Immunity

Emerging infectious diseases can drive rapid evolution. Epizootics allow the observation of evolution in real time, offering a unique window into the mechanisms by which natural selection creates local adaptation. Populations of frogs worldwide have declined precipitously in the decade since a virulent pathogen (the chytrid fungus Batrachochytium dendrobatidis, denoted Bd) was first discovered infecting frogs in Central America, Australia and New Zealand. Certain immune-system (major histocompatibility complex, denoted MHC) alleles confer specific resistance to pathogens.

The amphibian chytrid fungus will subject MHC alleles in frog populations to strong selection for their immunological defences against, or tolerance of, the pathogen. Consequently, populations should differ markedly in their genetic makeup before and after their exposure to Bd. The genetic changes should enhance frogs’ resistance to Bd, but also may modify other physiological characters that impact on their social systems, ecology and survival.

We are conducting research on how chytrid fungus affects Asian amphibian populations. The research tracks the spread of the pathogen to naive populations and examines selection for evolutionary responses in MHC genes that may confer immunity on infected individuals. The amphibian chytrid fungus only recently was discovered infecting frogs in Korea, its first documented appearance in mainland Asia. This provides a good platform for addressing basic and applied questions in disease ecology and conservation biology.