Data from: Ancestral chytrid pathogen remains hypervirulent following its long co-evolution with amphibian hosts

Many amphibian species around the world, except in Asia, suffer morbidity
and mortality when infected by the emerging infectious pathogen
Batrachochytrium dendrobatidis (Bd). A lineage of the amphibian chytrid
fungus isolated from South Korean amphibians (BdAsia-1) is evolutionarily
basal to recombinant global pandemic lineages (BdGPL) associated with
worldwide amphibian population declines. In Asia, the Bd pathogen and its
amphibian hosts have coevolved over 100 years or more. Thus, resilience of
Asian amphibian populations to infection might result from attenuated
virulence of endemic Bd lineages, evolved immunity to the pathogen or
both. We compared susceptibilities of an Australasian amphibian, Litoria
caerulea, known to lack resistance to BdGPL, with those of three Korean
species, Bufo gargarizans, Bombina orientalis and Hyla japonica, after
inoculation with BdAsia-1, BdGPL or a blank solution. Subjects became
infected in all experimental treatments but Korean species rapidly cleared
themselves of infection, regardless of Bd lineage. They survived with no
apparent secondary effects. By contrast, L. caerulea, after infection by
either BdAsia-1 or BdGPL, suffered deteriorating body condition and
carried progressively higher Bd loads over time. Subsequently, most
subjects died. Comparing their effects on L. caerulea, BdAsia-1 induced
more rapid disease progression than BdGPL. The results suggest that
genomic recombination with other lineages was not necessary for the
ancestral Bd lineage to evolve hypervirulence over its long period of
coevolution with amphibian hosts. The pathogen's virulence may have
driven strong selection for immune responses in endemic Asian amphibian
host species.