Some fungi are modern marvels of the natural world. The genus Pilobolus contains a special group of species that should be considered for the fastest organisms on the planet-relative to its small size. These fungi that inhabit grasslands have evolved a pretty unique form of spore dispersal that ensures a competitive edge over other coprophagous (dung feeding) fungi. To find some fungi I write about, one might have to travel to an exotic place on the planet, scouring the forest floor for days to come up with any signs of the organism. Pilobolus fungi however, can be found in temperate areas around the world where large herbivores roam.
Pilobolus fungi feed on the excrement of large mammals, but mostly specialize on cow and horse dung. The spores of these fungi only germinate once they pass through a digestive tract, so the goal of the fungus is not to disperse directly to fresh dung, but to vegetation that will be consumed by their mammal counterpart. Before their dung substrate dries up, these fungi create a water filled subsporangial vesicle that sits under a black sporangium. The sporangium of this species is much larger than the spores of other fungi, and is covered in calcium oxalate crystals. These hydrophobic crystals help the fungi adhere to moist vegetation as causes the sporangium to flip on to its sticky side.
Once clung to a blade of grass it (hopefully) becomes consumed by a grazing horse. The environment of the lower digestive system stimulates the sporangium into germination. This adaptation of spore activation gives this fungus a competitive edge. Once it is eaten, is has the entire pool of newly formed excrement to itself. Other coprophagous fungi and insects must locate dung after it is excreted. Pilobolus fungi on the other hand are already completely colonizing the dung and transforming it into usable sugars.
Pilobolus sp.
The direction the fungus grows is directed by light; another adaptation that ensures adequate dispersal. With the subsporangial vesicle acting as a lens, the fungus orients itself so the beam of light from the sun enters the lens and hits the base of its structure where carotenoid pigments are deposited. This phototrophic ability ensures the fungus launches the spore up in the air unimpeded, instead of directly into the ground, or into a nearby fencepost.
As it forms its asexual sporangium, its subsporangial vesicle fills with water allocated from the dung. Turgor pressure inside the vesicle reaches 7 ATM or higher to propel the sporangia from 0 to 20 km/h in just two microseconds. Since a single microsecond equates to on millionth of a second, the forces at play here are astronomical. The 20,000 G’s produced are equivalent to launching a human 100 times the speed of sound!! Click this link to see it in supper slow motion!
These primitive organisms are evolutionary feats in nature, and are capable of producing insane forces. The goal of this blog is to captivate people into appreciating the forest floor, which may seem mundane. Well, wait no longer, because now even poo is cool. That’s right, dung from horses or cattle may support species of fungi that literally launch cannons to complete their life cycle.