Magic mushrooms are fungi that produce psilocybin, a compound with breakthrough status for treatment of mental health disorders. Wood-degrading species of Psilocybe, such as P. subaeruginosa and relatives, have high concentrations of psilocybin but are discouraged for clinical production due to a temporary paralytic side effect known as Wood Lover’s Paralysis, the cause of which is unknown. We studied P. subaeruginosa over its partial distribution in Australia based on genomic analyses of 89 isolates to investigate population structure and species boundaries, examine allelic diversity at psilocybin loci, and test its centre of origin. Psilocybe subaeruginosa is structured by geography in Australia, but geographically separated populations are fully sexually compatible. Allelic diversity among populations, such as at mating compatibility loci, is likely a result of genetic drift and minimal gene flow since differentiation from a shared ancestor. Movement of woodchips, mulch, or plants has most likely spread genotypes of P. subaeruginosa locally within Australia and to the northern hemisphere. Species from the northern hemisphere, namely P. azurescens and P. cyanescens, clustered among Australian populations, indicating shared ancestry and supporting a hypothesis these taxa are conspecific with P. subaeruginosa. We identified high allelic diversity in genes of the psilocybin metabolic pathway and haplotypes of P. subaeruginosa with either one or two putatively functional paralogs of psiH, however the functionality of this gene duplication is yet to be determined. Our study provides insights into the evolutionary history and species boundaries of P. subaeruginosa, which has a centre of origin in Australasia.

The host-associated microbiome plays a significant role in health. However, the roles of factors such as host genetics and microbial interactions in determining microbiome diversity remain unclear. We examined these factors using amplicon-based sequencing of 175 Thoropa taophora frog skin swabs collected from a naturally fragmented landscape in southeastern Brazil. Specifically, we examined (1) the effects of geography and host genetics on microbiome diversity and structure; (2) the structure of microbial eukaryotic and bacterial co-occurrence networks; and (3) co-occurrence between microeukaryotes with bacterial OTUs known to affect growth of the fungal frog pathogen Batrachochytrium dendrobatidis (including anti-Bd bacteria commonly referred to as “antifungal”). Microbiome structure correlated with geographic distance, and microbiome diversity varied with both overall host genetic diversity and diversity at the frog MHC IIB immunity locus. Our network analysis showed the highest connectivity when both eukaryotes and bacteria were included, implying that ecological interactions occur among Domains. Lastly, anti-Bd bacteria did not demonstrate broad negative co-occurrence with fungal OTUs in the microbiome, indicating that these bacteria are unlikely to be broadly antifungal. Our findings emphasize the importance of considering both Domains in microbiome research, and suggest that probiotic strategies for amphibian disease management should be considered with caution.

Habitat fragmentation and infectious disease threaten amphibians globally, but little is known about how these two threats interact. In this study, we examined the effects of Brazilian Atlantic Forest habitat fragmentation on frog genetic diversity at an immune locus known to affect disease susceptibility in amphibians, the MHC IIB locus. We used a custom high-throughput assay to sequence the MHC IIB locus across six focal frog species in two regions of the Atlantic Forest. We also used a molecular assay to quantify infections by the fungal pathogen Batrachochytrium dendrobatidis (Bd). We found that habitat fragmentation is associated with genetic erosion at the MHC IIB locus, and that this erosion is most severe in frog species restricted to intact forests. Significant Bd infections were recovered only in one Atlantic Forest region, potentially due to the relatively higher elevation. In this region, forest specialists showed an increase in both Bd prevalence and loads in fragmented habitats. We also found that reduced population-level MHC IIB diversity was associated with increased Bd infection risk. On the individual-level, MHC IIB heterozygotes (by allelic genotype as well as supertype) exhibited a reduced risk of Bd infection. Our results suggest that habitat fragmentation increases infection susceptibility in amphibians, mediated at least in part through loss of immunogenetic diversity. Our findings have implications for the conservation of fragmented populations in the face of emerging infectious diseases.