White-nose disease is a fungal disease in bats that is caused by Pseudogymnoascus destructans. The pathogen is widely distributed in Eurasia and has been recently introduced to North America. Previous studies have explored host–fungus interactions as well as interaction between the fungus and environmental conditions. In this study, Puechmaille and colleagues investigated pathogen variability and discovered the existence of two cryptic species of the pathogen. The authors analysed a reference collection of 5,479 isolates that originate from 264 sites in 27 countries, and they identified a clear separation into two clades, termed Pd-1 and Pd-2. Both clades share the same geographical range, and both cause white-nose disease. Interestingly, the authors showed an association between the fungal clades and the bat host species, which suggests that host specialization is a determinant for their ecological niches. Genome analysis revealed monophyly of the two clades, widespread recombination within the clades and substantial genomic structural differences between the clades. Finally, the strong population structure enabled the authors to trace back the most likely source population of the North American introduction to a region in western Ukraine.
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