Squirrel consuming “poisonous” mushrooms

Abstract

The representative toadstool Amanita muscaria plays an important role in maintaining forest ecosystems by forming mutualistic associations with a variety of trees. A muscaria is also known for the poisonous properties of its hallucinogenic constituents, namely, ibotenic acid, muscimol, and muscarin. Serious cases of poisoning in humans may involve deliria, hallucinations, seizures, and (rarely) death. A typical symptom is visual distortion of the size of objects, a phenomenon that formed the basis of the mind-altering events described in Lewis Carroll’s 1865 novel Alice’s Adventures in Wonderland. Interestingly, we observed a Japanese squirrel (Sciurus lis) routinely feed not only on A muscaria but also on other Amanita species that are also poisonous to humans. This squirrel returned to feed on Amanita fruiting bodies for several days, indicating that it could safely consume the “poisonous” mushrooms. The ecological roles of fungal toxins remain largely unexplored. One possible role is to deter fungivores. However, fungivores are not always disadvantageous to Amanita, because they may disperse intact spores via their digestive tracts. Perhaps Amanita mushrooms facilitate mutualisms with toxin-resistant squirrels, which can disperse viable spores, while deterring toxin-susceptible enemies, which could negatively impact spore survival. If so, potential dispersal of fungal spores by squirrels is analogous to a seed dispersal mutualism, in which a plant offers a reward to an animal as a seed disperser. How do squirrels safely eat Amanita mushrooms? What role do squirrels play in Amanita spore dispersal? How would squirrel-assisted spore dispersal contribute to the establishment of ectomycorrhizal relationships within these ecosystems? These questions warrant further investigation.