Truffles should be the poster child of ecology. These unassuming fungi engage in countless forest interactions so I feel that every aspiring ecologist should understand how truffles function in ecosystems around the world. These subterranean (hypogeous) fungi engage in mutualisms with suitable trees, with the fungi finding rare soil nutrients and sending those materials to the roots of its tree host. The trees reward their fungal symbiont with sugar fixed through photosynthesis. The ecological interactions of these amazing fungi do not end there. Unlike most higher fungi that release millions of spores into air currents daily, these underground fungi hold on to their spores hoping to attract hungry mammals. When their mammalian counterpart does find them, they consume the tasty morsels, thereby vectoring fungal spores to new areas of the forest floor. If these mammals defecate near suitable ectomycorrhizal trees, then the spores may germinate, and start the process all over again.
I have written about truffles and their different but analogous mammalian dispersers already in this blog. But I have yet to touch on the wide diversity of ‘false truffles’. The genus Tuber produces the most prized and expensive truffles. These ‘true truffles’ can go for about $3000.00 a pound in USD! Other hypogeous truffles that have evolved separately, that function in ecosystems remarkably similarly don’t taste as good, are not as sought after, and have since been dubbed as the false truffles. But the fact holds, that there are a ton of these false truffles that grow all around the world. One of the most widespread false truffles that grows in North America is Elaphomyces muricatus.
Most of the time, Elaphomyces muricatus goes unnoticed. This is unsurprising given their subterranean nature. If you do your own searching on the internet, many of the photos you find online will actually depict mycoparasites growing out the bulbus fungal tissue. There are several Elaphocordyceps species that fruit from these hypogeous fungi, and penetrate through the surface of the forest floor. Mycophiles can then easily find these parasites, and realize that they are growing from these truffle-like fungi.
Elaphomyces actually means “deer fungi,” which highlights this species main method of dispersal. These common hypogeous fungi were once sold as an aphrodisiac, because they were constantly found in areas where deer have rutted. This really is the human thought process at its best; if it makes deer horny, it should make us horny! It really doesn’t though. But there is a chance that the fungus could mimic mammalian pheromones. The most prized Tuber species produce a chemical compound known as alpha-androstenol. This compound is easily picked up by pig's noses since it is a pheromone produced in the saliva of rutting boars as well as other mammals that forage the forest floor for their food. It really isn’t that farfetched to see why this species might also produce a compound that its mammalian disperser can easily detect.
In the last 1,000 years, man has greatly reduced the predators that once preyed on deer. As a result, deer populations are at an all-time high, even with a wide hunting season implemented. A side result is the spread of Elaphomyces muricatus. Though, since many North American forests aren’t kept in check by predators, plants are overgrazed. These fungi are not limited by dispersal, but may be limited by habitat in the future. We might see dense numbers of these false truffles now, but spores landing near healthy suitable trees that haven’t been devoured by hungry ungulates might be a rare occurance in the future. As deer strip away the leaves of trees engaged in a mycorrhizal mutualism, less sugar can be allocated to the fungal symbiote and the mutualism may dissociate, or not even begin in the first place.
Elaphomyces muricatus is a fascinating species that I’m glad I learned about. Again, in the world of biology, convergent evolution is nature’s way of telling us that these specific, forms and functions have worked really well in the past, and will keep on promoting fitness well into the future. Hypogeous truffle-like fungi have evolved separately several times over for many reasons. For one, they hold on to water better than aboveground fruiting fungi, since they are located in cool, moist, subterranean habitats away from moisture stripping wind currents. Their mycorrhizal lifestyle isn’t threatened either, as plants and fungi have been closely interacting for over 400 million years. And depending on mammalian dispersal also seems to be a fruitful evolutionary strategy, as these active and hungry animals will continue dominating forest habits for millions of years to come. Elaphomyces muricatus may not taste as good as Tuber species, but they do function almost exactly the same.