Poronia punctata is a fascinating ascomycete species that is becoming exceedingly rare to find. Commonly known at the nail fungus, it is not to be confused with other keratinous fungi that live on human toenails. The father of modern taxonomy, Carl Linnaeus first described this small fungus as Peziza punctata in 1753. Just under a century later in 1849, Swedish mycologist and botanist Elias Magnus Fries closely examined the species, which lead to its transfer into the genus Poronia. I have found a few online sources that have mentioned its rare occurrence in the western United States, but its natural distribution is throughout Europe and the most Northwestern parts of Eurasia.
P. punctata specializes in a coprophilous or dung feeding ecology, and seems to have a fondness for horse dung. I have already talked about two different [1, 2] species of fungi that have evolved coprophilous lifestyles, but both of them have adapted mechanisms to enhance early colonization. P. punctata however is a late colonizer, and thus has evolved chemicals that can reduce competitor growth when it finally colonizes a suitable substrate.
Poronia punctata found in Italy by Davide Puddu.
This species now rare occurrence really is a great example of how minor changes in human development may have large consequences not only for entire communities of organisms, but especially for individual species. Before the development of automobiles, Europeans depended on their equine counterpart for transpiration. You can imagine how abundant this species was, with the ridiculous amount of horse poo littered throughout European cities. Nowadays, the species is really struggling, being categorized as Near Threatened on the Red Data List in 2006. Not only are there fewer horses in this automobile dominated era, but modern horse keeping practices limit the late colonization of this species. Other, early colonizing species are not as impacted by these modern practices, since they have a better chance of carrying out their life cycle before their substrate is scooped up by maintenance working in horse stables.
This specimen was actually found in Chile! By Giuliana Furci.
Humans have an increasing influence on Earth’s environments. Before learning about this species, I hadn’t thought about additional strategies that might have evolved in coprophilous fungi. The dung feeding fungi I learned about had the same strategy; get to the substrate before other competitors. The sooner an organism reaches a suitable substrate, the more available nutrients are within that substrate. Poronia punctata however has a different later stage strategy. Instead of dispersing to substrate fast, it hosts genes that encode for the synthesis of a particular chemical (+)-Isoepoxydon.
The isolated antifungal compound. Gloer and Truckenbrod 1988.
Once P. punctata finally disperses to suitable substrate, there are almost always other fungal colonizers present. Researchers J. Gloer and S. Truckenbrod hypothesized that this fungus produces chemicals with antifungal properties that allow it to carry out its late colonizing ecology. Using mass spectrometry and other ridiculous sounding methods, (proton and carbon nuclear magnetic resonance spectroscopy), these scientists isolated and identified the compound and tested its antifungal performance. (+)-Isoepoxydon was found to significantly reduce the growth of other fungi, ultimately giving this late colonizing coprophilous species the competitive edge once it occupies its substrate.
Semi-wild horse in the New Forest in England.
With the expansive distribution of wild horses and their ancestors before humans domesticated the mammals for their own use, this species was once exceedingly common. However, this late colonizing ecology is limiting this species in a heavily human dominated era. Overall, the replacement of horses with automobiles and modern standards of cleanliness have made this species a rarity. There is but one place in England where this species is doing well-the New Forest. In the New Forest, semi-wild horses roam, and horse droppings aren’t picked up through human intervention. Here, the late colonizing Poronia punctata can disperse and outcompete the coprophilous colonizers before it.