Amanita thiersii and Amanita foetens are closely related but genetically and geographically distinct taxa, leaving the origins of A. thiersii and its range expansion enigmatic

Authors: DUNKIRK, NORA - University Of Wisconsin; WANG, YEN-WEN - Yale University; Drott, Milton; ELMORE, HOLLY - Rethink Priorities; ROBLEDO, GERARDO - Universidad Nacional De Cordoba; TULLOSS, ROD - New York Botanical Garden; PRINGLE, ANNE - University Of Wisconsin

Submitted to: F1000Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2023
Publication Date: 7/20/2023
Citation: Dunkirk, N., Wang, Y., Drott, M.T., Elmore, H., Robledo, G., Tulloss, R.E., Pringle, A. 2023. Amanita thiersii and Amanita foetens are closely related but genetically and geographically distinct taxa, leaving the origins of A. thiersii and its range expansion enigmatic. F1000Research. https://doi.org/10.12688/f1000research.134814.1.
DOI: https://doi.org/10.12688/f1000research.134814.1

Interpretive Summary: The fungus, Amanita thiersii, has been invading lawns and golf courses in Texas and is now spreading across the United States. Questions have remained as to weather this fungus is introduced or is an endemic species that is expanding its range. We used morphological and molecular biological approaches to examine this fungus and compare it to the close relative, Amanita foetens. We demonstrate that the genetic diversity of the American fungus is strikingly low. While this is consistent with an introduced fungus, and other metrics are strikingly similar between the two fungi the origins of A. thiersii remain enigmatic.

Technical Abstract: The decomposer Amanita thiersii was originally described from a Texas lawn. Over time, the fungus appears to have spread out of Texas, but whether A. thiersii is an introduced and invading fungus or an endemic expanding its range remains an open question. A striking morphological similarity between A. thiersii and the South American A. foetens, another large, white mushroom, led us to question whether the two species are in fact the same; we hypothesized A. thiersii was simply an A. foetens introduced from Argentina. First, we compared the original species descriptions of both taxa. Morphological descriptions suggest the two taxa are nearly indistinguishable. Next, we used databases associated with iNaturalist, Mushroom Observer to plot the global ranges of A. thiersii and A. foetens, discovering new reports of A. thiersii in Mexico and an expanded range for the fungus in the United States. A. thiersii appears to have spread north to Wisconsin and to have reached the East Coast. Geographic ranges of the two taxa seem distinct and not overlapping, although different naming conventions in the different databases cause confusion. Finally, we sequenced three genomes: a U.S.A. A. thiersii, an isotype of A. foetens, and an Argentinian mushroom tentatively identified as A. thiersii. We built phylogenies using publicly available data of other Amanita taxa and two approaches: phylogenomics, and consensus trees of multiple, independent loci. Phylogenies suggest the genomes of mushrooms collected in U.S.A. are different from Argentinian genomes. Because the genetic diversity of U.S.A. thiersii appears to be very low, we also searched for mating type loci, which appear to be present in some genomes and absent in others. While the two species are strikingly similar, each is geographically and genetically distinct, leaving the origins of A. thiersii enigmatic.