The Wonderful World of Fungi, Part IV
Coprophilous Fungi & Succession on Dung
By: H. Wayne Shew, Ph.D.
NAB Certified Pollen Counter
Dung is more than you might think — not just that smelly, nasty stuff that is terrible to get on your shoes. Neither is it merely an important source of organic fertilizer for plants. It turns out that there are some fungi that love dung and relish the opportunity to live on and in it. In fact, some fungi absolutely require it because it serves as their food source and habitat. Those fungi that use dung as their source of nutrition are known as coprophilous fungi. The word comes from the Greek words for dung (copro from kopros) and love (philos) because these fungi “love” dung, the way you might love fillet mignon or strawberry shortcake.
Coprophilous fungi are saprobes that grow on animal dung. There are numerous genera of fungi that use herbivore feces as a food source and these coprophilous fungi are found in all the major fungal groups (Divisions: Zygomycota, Ascomycota, Basidiomycota, Deuteromycota). Even though most coprophilous fungi are found on herbivore dung, there are some species of fungi that grow on omnivore dung and some are even found on some types of carnivore dung. Those species growing on omnivore and carnivore dung are typically in the genus Chaetomium. Regardless of the source of the dung, coprophilous fungi all share a common life cycle. The reproductive spores of the fungus must first be ingested by the animal producing the appropriate dung for that species of fungus. The spores must then pass through the digestive tract of the animal and then germinate and grow on the dung outside of the animal’s body. The fungus then forms spores in fruiting structures produced on the dung, and these spores are released into the surrounding environment and the life cycle begins anew.
Why dung? Animal dung is a rich source of protein and carbohydrates. Since all fungi are heterotrophs, (that is, they obtain their energy and molecular building materials from organic sources), it is necessary to have a source of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur, the major elements needed to make molecules needed for growth and survival of all living things. Animal feces is a great repository of nitrogenous compounds and sugars, as well as other carbohydrates such as starch and cellulose. Hence, dung turns out to be a beautiful place to live and grow, at least if you are a coprophilous fungus.
Some coprophilous fungi require specific types of animal feces to complete their life cycle; for example, Coprinus radiatus and Panaeolus campanulatus are almost exclusively restricted to horse dung. Other coprophilous fungi such Panaeolus sphinctrinus can grow on almost any feces and even on very fertile soil.
One of the fascinating aspects of dung ecology is the “succession” of fungal species that can be observed on the dung. Ecological succession occurs within the grazing food chains and decomposing food chains of all ecosystems; dung is one of the most interesting of these microhabitats (microecosystems) in which succession takes place. A regular (and I believe extremely interesting) sequence (succession) of organisms serve to decay (decompose) the dung of herbivorous animals. The progression begins with bacteria, then the zygomycetes appear, then ascomycetes, and the process ends with basidiomycetes. These organisms appear at roughly weekly intervals in laboratory experiments. The “typical” genera that you observe in the succession on the dung of horses or cows are: Bacillus, a rod-shaped bacterium; Pilobolus, the “hat thrower,” a Zygomycete; Ascobolus, a cup fungus, an ascomycete; and Coprinus, the “inky cap mushroom,” a basidiomycete.
Most of the fungi that decompose the dung of pasture animals, like horses, cows and other herbivores, show the same kind of intricate adaptions involving (1) activation of the spores during their passage through the animal’s gut, (2) rapid growth on the rich source of organic materials (food) so conveniently provided in the deposited dung, (3) light-oriented violent discharge and dissemination of spores, and (4) the capacity to adhere to surrounding vegetation and resist drying and sunlight until they are ingested by an herbivore to start the cycle again.
One particularly remarkable fungus that is part of the succession on horse and cow dung is Pilobous, the hat-thrower or shotgun fungus. This fungus produces a sporangium that sits atop a subsporangial swelling at the tip of a stalk called a sporangiophore that is itself some 2-4 centimeters high. This reproductive structure is phototactic, and in fact is quite accurate at shooting the sporangium towards a light source. The sporangium is violently released when the subsporangial swelling bursts and the sporangium accelerates from zero to 45 mph during the first millimeter of travel, an acceleration of 20,000 g. The sporangium can travel through the air for up to two meters before landing on, and sticking to vegetation nearby. To appreciate this remarkable feat of discharging the sporangium at such great speeds, it is important to be able to see it slowed down using high-speed photography. The websites below are of videos showing the hat-thrower fungus forcibly throwing its hat, or shooting the sporangium away from the dung on which it is growing. I urge you to take a few minutes and look at them. I think you will be fascinated and perhaps begin to think of dung in a whole new light after you do.
(A collection of YouTube videos of the hat-thrower fungus.)
(This video is a must see; highly recommended.)