Warning colouration in plants and funghi
In the period of austerity after the Second World War, the British government encouraged the public to supplement rationed diets with wild mushrooms, which were full of vitamins and nutritional value.
However as we all know, not all mushrooms are edible and before guide books, humans had to use folklore tips such as such as only eating ‘peelable’ mushrooms to avoid poisoning themselves. Such folk wisdom is not known to be completely reliable in avoiding lethal fungi!
Up until now, the subject of poisons in mushrooms has been covered by some medical publications, but has received little attention from general biologists, and no book has posed the question: why exactly are some mushrooms poisonous?
However, Dr David Wilkinson, LJMU’s Reader in Environmental Science, has conducted the first formal analysis of the ecological and morphological traits of mushrooms in North America, Mexico, and Europe, in collaboration with Canadian colleagues.
The study considers several issues, such as whether or not poisonous mushrooms alert predators to their toxicity, how animals can differentiate between edible and noxious fungi, and also the intriguing possibility that some poisonous species of mushrooms have evolved warning odours (and perhaps tastes).
Many animals have an association between danger and conspicuousness, known as ‘aposematism’, a defence mechanism which advertises their unpalatability to predators. Indeed, there have been suggestions that conspicuous warning signals may have similarly evolved in plants to deter would-be diners.
Dr Wilkinson’s study attempted to discover if the same is true in mushrooms, a theory which is consistent with the fact that there are several brightly coloured poisonous mushrooms, such as the iconic red and white ‘fly agaric’.
By using modern phylogenetics (the study of gene lineages), Dr Wilkinson has been able to assess how frequently poisons have evolved. A previously unknown fact highlighted by his research is that poisons have appeared, disappeared and reappeared many times in the evolutionary history of mushrooms.
The study has revealed no evidence that poisonous mushrooms consistently signal their unpalatability through visual traits or odours. Several authors had suggested this previously but this new work was the first study to demonstrate it by formal statistical analysis. The most surprising result of this work was that there was a formal statistical relationship between fungi that were poisonous to humans and fungi that were commonly described as smelling ‘bad’ to the human nose. This raises the intriguing possibility that poisonous fungi ward off potential predators, such as deer, by using smell.
The findings of the research paper entitled 'Explaining Discorides’ “Double difference”: why are some mushrooms poisonous and do they signal their unprofitability?', were published in American Naturalist in 2005. The title of the paper refers to an early description of poisonous mushrooms by Discorides – a Greek surgeon in Nero’s army in the first century AD. The research attracted media interest with articles describing the results appearing in both the leading scientific journal Nature and Natural History magazine.