Is the fungus Amanita thiersii an invasive species? Using genomes to solve a decades old mystery

Background/Question/Methods

Species’ introductions often lead to invasions, and invasive species are one of the top five threats to Earth’s biodiversity. Invasive fungi have not garnered as much attention as invasive vertebrates and plants, but their impacts on ecosystem services and native species can be tremendous. Researchers interested in the decomposer species Amanita thiersii recently used herbarium records to track the apparent spread of this species out of Texas and across the southern and midwestern United States. But morphological similarities between A. thiersii and another Amanita, the Argentinian A. foetens, raise two burning questions: are these two species actually the same species, and was the species introduced to the U.S. from Argentina? Our lab has sequenced the genomes of three mushrooms, an Amanita thiersii from Kansas; the isotype specimen of the Argentinian A. foetens, and a sporocarp collected in Argentina in 2014, originally identified as A. thiersii. I have used the Burrows-Wheeler Aligner to align the raw genome sequences at marker loci commonly used to build phylogenies: nucSSU locus, nucLSU locus, ITS locus, mtSSU locus, and mtLSU locus.

Results/Conclusions

Preliminary results based on the ITS locus show only two SNPs (Single Nucleotide Polymorphisms; 0.3% difference) between A. thiersii from U.S. and A. foetens from Argentina. If the sequences for those sporocarps collected in Argentina match closely ( >97% match) with A. thiersii from the Texas range, we can conclude that A. thiersii and A. foetens are the same species. If A. thiersii was introduced to the U.S. from South America, its geographic spread and the dramatic increase in its population size over recent decades would clearly define it as an invasive species. Especially as conservation efforts ramp up to stop the spread and effects of invasive species, it is vital to be able to differentiate between the native and invasive ranges of fungi. Our data are providing a unique opportunity to determine the ecological dynamics of an Amanita fungus currently spreading in North America.