Introduction
Mushrooms (Agaricomycetes, Basidiomycota) disperse large quantities of wind-borne spores (Dam, 2013), yet populations of many different species are structured by geography (Amend, Garbelotto, Fang, & Keeley, 2010; Branco et al., 2017; Dabao Sun et al., 2023). These geographically isolated populations may form allopatric species if mating compatibility ceases. Mushrooms are typically obligately sexual (heterothallic), and mating compatibility is either tetrapolar, in which alleles at two independent loci must differ for gametes to fuse, or bipolar, controlled at one locus (Coelho, Bakkeren, Sun, Hood, & Giraud, 2017). Mating-compatibility loci have high allele diversity and long allele residence times (Skrede, Maurice, & Kauserud, 2013; van Diepen, Olson, Ihrmark, Stenlid, & James, 2013), and this diversity is maintained across populations by negative frequency selection that favours rare mating types, with minimal divergence of functional parts of mating genes that control compatibility (Peris et al., 2022). The relationship between speciation and erosion of mate compatibility in reproductive isolation needs better understanding to delineate populations from species of Basidiomycota.
Mushrooms that produce psilocybin, magic mushrooms, occupy diverse environmental niches as saprotrophs that degrade leaves, wood, and dung (Stamets, 1996). A key diagnostic character of magic mushrooms is a blueing reaction, due to oligomers of psilocin that form when psilocybin is dephosphorylated and oxidised after tissue damage (Lenz et al., 2020). Psilocin, the active metabolite of psilocybin, binds to serotonin receptors, which are the targets hypothesised to protect magic mushrooms against fungivory by metazoans (Reynolds et al., 2018). The etymology behind epithets of wood-degrading magic mushrooms, e.g., P. azurescens , P. cyanescens , and P. subaeruginosa , describes their strong blueing reaction and these mushrooms have some of the highest concentrations of psilocybin (Gotvaldová et al., 2022).
The Oregon Psilocybin Advisory Board discouraged commercialisation of wood-degrading species of Psilocybe as in some cases a side effect temporarily paralyses users during a psilocybin experience (Abbas et al., 2021). The cause of ‘wood lover’s paralysis’ is unknown (Dörner et al., 2022). Dörner et al. (2022) and McTaggart et al. (2023) showedpsiH , a gene in the psilocybin pathway that converts tryptamine into 4- hydroxytryptamine (Fricke, Blei, & Hoffmeister, 2017), is duplicated with up to three homologs in wood-degrading species ofPsilocybe , compared to a single copy in P. cubensis . McTaggart et al. (2023) hypothesised these gene duplications may impact the production of psilocybin and its analogues, however, there is no evidence that links the psilocybin pathway to wood lover’s paralysis, and Dörner et al. (2022) suggested the symptoms are likely not linked to tryptamines.
Psilocybe subaeruginosa was described from national parks and natural environments in Australia (Cleland, 1927). It has taxonomic priority in a complex of closely related, potentially conspecific species described from Australia (P. australiana , P. eucalypta , and P. tasmaniana ), New Zealand (P. makaroraeand P. weraroa ), and the northern hemisphere (P. allenii ,P. azurescens , and P. cyanescens ) (Borovička, Noordeloos, Gryndler, & Oborník, 2011; Gotvaldová et al., 2022). The morphological diversity of P. subaeruginosa in Australia encompasses phenotypes of taxa described in the northern hemisphere (Fig. 1). Psilocybe allenii and P. cyanescens behave as invasive taxa in the northern hemisphere, occurring in planted garden beds rather than undisturbed ecosystems (Borovička, Rockefeller, & Werner, 2012; Dennis & Wakefield, 1946), and having low genetic diversity among populations (Gießler, 2018).
Psilocybe subaeruginosa has a wide distribution across Australia, occurring from southeast Queensland at its northernmost extent to Tasmania, South Australia, and Western Australia. We examined populations of P. subaeruginosa across its eastern distribution in Australia to test hypotheses (i) that it has a centre of origin in Australia, (ii) that it is conspecific with species in the northern hemisphere, (iii) that populations in Australia are structured by geography, and (iv) that selection shapes the genes in the psilocybin pathway. To do so, we used population genomics and mating compatibility to compare relationships among Australian populations and included reference sequences of P. azurescens and P. cyanescens to test conspecificity with taxa in the northern hemisphere. Our study examines how fungal species connectivity is maintained across geographic boundaries and provides new knowledge on the centre of origin of wood-degrading species of Psilocybe .