DNA and the Marsupial Mushrooms

JULY meeting of Main Club

Our speaker was Elaine Davison, a long-time member of our Club. Dr Davison is Adjunct Professor in the School of Molecular and Life Sciences at Curtin University and a research associate at the WA Herbarium. She has worked in South Australia and the UK and in WA for DBCA and the Department of Agriculture (DAFWA). As a plant pathologist she has researched fungal diseases of woody plants in native ecosystems and in forestry and horticulture, including the management and control of diseases. And as a mycologist she has studied and continues to study Australian fungi, in particular Amanita species. Elaine spoke about her research into the amanitas, which along with slime moulds and fungi of the arid regions, is one of her particular interests.

This research is being funded through Lotterywest and the Club.

Elaine first talked about what a fungus is. A modern ‘Tree of Life’, far from the old models that show every living thing classified as either plant or animal, shows fungi as one of many major “kingdoms”, and more closely related to animals and sponges than to any of the plant groups. Moreover, they are not at all closely related to things we may think of as fungi, such as the oomycetes (water moulds) and the slime moulds. Fungi are composed of hyphae, which are threads, typically 10 microns thick. A mass of hyphae has a large surface area relative to its mass, and from this surface it can excrete enzymes to digest and absorb the substrate. Hyphae can either diverge from one another so as to spread out, or they can mass together to form thicker structures including macroscopic fruiting bodies which produce and distribute spores.

Some fungi are parasites, causing plant disease, others are saprophytes, which break down and recycle dead material, and others are mutualists (having mutual benefit to both organisms), such as lichens, endophytes and mycorrhizae. The amanitas are an example of mycorrhizal fungi, which attach to the roots of plants and bring various nutrients to their host while receiving sugars in return.

There are more than 100,000 species of fungi that have been named so far. They range from edible to highly toxic. Even some members of the same genus vary in this way, and identification can be difficult. The genus Amanita is one of those, with the Death Cap (Amanita phalloides) for example, containing deadly amatoxins which accumulate in the liver. Poisoning symptoms occur 24 hours later—too late to remedy!

Identification of fungi can be difficult if it’s just by a casual look at the easily-visible part—the “fruiting” or spore-bearing body. This is because its shape, size and colour, though useful for identification, can vary within one species, according to such things as its stage of development. (Colour is not important to the survival of the fungus.) Therefore microscopic examination is often used, such as distinguishing spore types—different colours and shapes of sexual and asexual spores. Also, spore prints are diagnostic, showing the spore colour and the gill pattern. (Spacing and vertical orientation of gills are critical for the dispersal of spores.) Other diagnostic features are the veils, ring and volva, the texture of the cap and the type of substrate it is growing on. But in addition to all these features, we now have DNA analysis to help in identification.

Elaine explained how DNA analysis helped solve a problem of identification and classification within the genus Amanita. After a long search for the origin of a historical collection of a specimen of Amanita peltigera from “Stirling West”, she discovered that it was not in WA but in South Australia. DNA showed that those found in SA and in WA were in fact from disjunct populations of the same species. Moreover, the research indicated that the amanitas have ancient Australian origins. It shows that Arenaria—a section of the Amanita genus—is an ancient group, only known from southern Australia, which split from South America and Antarctica 33 million years ago.

DNA analysis, Elaine says, has resulted in better descriptions of named species and new species. This is important because in the early days, names of European fungi were often carelessly and wrongly applied to Australian fungi. She added that there are unfortunately very few mycologists in this country to study “marsupial” (i.e. Australian) mushrooms.

Mike Gregson