Spathularia flavida, more commonly known as the yellow earth tongue is an interesting looking fungus that is found all over temperate ecosystems in the northern hemisphere. It acquires nutrients from detritus in conifer dominated forests, by feeding on pine needles and woody debris from these acidic environments. Due to this species small stature, inedibility, and ephemeral nature, it is widely overlooked, and never truly gets the appreciation it deserves. Its widespread distribution and commonality not only indicates the availability of suitable substrates it can grow from, but also shows some adaptive traits it has evolved that have greatly enhanced its fitness.
A recent 2014 study utilizing advanced genetic techniques reveal how this species family, the Cudoniaceae diversified over time. Using 111 fungal samples from around the world, these researchers built a detailed phylogenetic tree and showed when the Cudoniaceae arrived on Earth’s scene. As it turns out, these data suggest that the Cudoniaceae diverged around 28 million years ago, during the Paleogene. Besides uncovering when these species began interacting with the forest floor, this research also identified the approximate location of divergence; Eastern Asia.
Several global events ensued shortly after its divergence during the Oligocene, ultimately leading the ancestors of Spathularia flavida to rapidly diversify into the species we see throughout Earth’s ecosystems today. These Oligocene events include global cooling and the uplift of the Tibetan plateau. Both events rapidly changed Eastern Asia’s climate. Some of those species that adapted spread throughout the northern hemisphere, while the others who didn’t evolve fitness enhancing traits in the face of these climate alterations perished.
A likely trait conserved over millennia include the ability Spathularia flavida has to produce volatile secondary compounds when Arthropods begin gnawing on its tissue. In 2006 Taizo Nakamori and Akira Suzuki set off to study the claim that injured fruiting bodies of the species featured here today produce chemicals that repel mycophagy. The arthropods within the subclass Collembola, also known as the springtails have an even more widespread distribution than Spathularia flavida. These more ancient springtails have been interacting with the forest floor nearly 400 million years before this yellow earth tongue, so the ancestors of these fungi have had more than enough time to evolve compensatory mechanisms against the tiny arthropods.
These researchers conducted behavioral assays by cutting the fruiting bodies of several yellow earth tongue specimens and introducing the injured fungus to feeding springtails. The behavior of the springtail was then analyzed between the presence of the cut fruiting bodies and the uncut controls. If the arthropod moved out of the 15mm diameter beneath the injured fungus, it was then recorded to have a distributional response. Interestingly, the springtails introduced to uncut Spathularia flavida had zero response, having none of them being perturbed by the fungus. Oppositely, nearly half of the springtails that were presented with the injured fungus had a distributional response. All of the springtails in close proximity to the injured fruiting bodies altered their behavior in one way or another, with all of them ceasing to feed at least once.
These results ultimately show that once injured, this attractive fungus produces volatile compounds that enter the air. It is speculated that strong odors deter mycophagy from springtails, and that this fungal trait has been conserved for millions of years. If the smell can deter mycophagy, then we can predict that the taste has an even stronger influence on the feeding animal’s behavior. Small, overlooked fungi emerging from the forest floor almost always have a fascinating backstory. To find out about a species evolution and fitness enhancing traits, you just have to dig a little.