Phylogenetics of a Fungal Invasion: Origins and Widespread Dispersal of White-Nose Syndrome
Globalization has facilitated the worldwide movement and introduction of pathogens, but epizoological reconstructions of these invasions are often hin- dered by limited sampling and insufficient genetic resolution among isolates. Pseud- ogymnoascus destructans, a fungal pathogen causing the epizootic of white-nose syndrome in North American bats, has exhibited few genetic polymorphisms in pre- vious studies, presenting challenges for both epizoological tracking of the spread of this fungus and for determining its evolutionary history. We used single nucleotide polymorphisms (SNPs) from whole-genome sequencing and microsatellites to con- struct high-resolution phylogenies of P. destructans. Shallow genetic diversity and the lack of geographic structuring among North American isolates support a recent introduction followed by expansion via clonal reproduction across the epizootic zone. Moreover, the genetic relationships of isolates within North America suggest widespread mixing and long-distance movement of the fungus. Genetic diversity among isolates of P. destructans from Europe was substantially higher than in those from North America. However, genetic distance between the North American iso- lates and any given European isolate was similar to the distance between the indi- vidual European isolates. In contrast, the isolates we examined from Asia were highly divergent from both European and North American isolates. Although the de- finitive source for introduction of the North American population has not been con- clusively identified, our data support the origin of the North American invasion by P. destructans from Europe rather than Asia.