Dung through the Ages
This is a tale of tiny fungi that grow on dung.
Sporormiella photo courtsey Alain Brissard
Dung is a great substrate for fungi and the fungi have developed several clever strategies to optimize this life style. For a start they decompose (i.e. eat) the non-digested parts of grasses and other vegetable matter that pass through a herbivore’s stomach and gut. Then they shoot or squirt their spores beyond the patty on which they are growing onto the grass around it, and there they wait for a cow/horse/mammoth/deer etc. to eat that particular clump. Once the spores are inside the herbivore’s digestive system, they can make their way to the exit along with their favorite substrate to start a new life cycle. This process calls for some adaptations of the spores. They are often surrounded by a gelatinous mass, which makes them stick to the grass, and also gives them some protection during the passage through the animal. The spore walls themselves are thick and dark brown or black from melanin. This gives protection from the sun, just after they have been shot off, and from the chemical onslaught in the herbivore’s stomachs where enzymes and acids attack the grass cell walls. The chemicals in the animal’s innards are also essential to make many of these fungal spores germinate. The dark, thick spore walls are not easily broken down and mean that the spores can stay around in the environment for a long time.
Sporormiella, the heroine of our story, forms tiny, pear-shaped black fruit bodies that stick out from the dung surface. The spores are easy to recognize. Each dark brown spore consists of a row of four to eight partial spores, which are completely covered by a thick gelatinous layer. Each partial spore has an s-shaped slit for germination purposes. This is a very widespread fungus, occurring worldwide on herbivore dung. And, the beauty is that these spores can still be recognized after thousands of years! This remarkable discovery means that we can deduce what kind of animals were roaming the earth, without seeing any fossil bones! The fungus supplements the information that various kinds of pollen give us about the changes in vegetation and that charcoal remnants, which can also be identified, tell us of fires.
Throughout North America, Sporormiella spores were abundant at the end of the last ice age when many different genera and species of big grazing animals were flourishing, including mammoth, American horses, western camel and llamas. Around 14,500 years ago their numbers started to drop as a first indication that the herbivores were vanishing. After that charcoal appears in the soil profiles: fires are raging. Is more flammable material available when herbivores are fewer in numbers and species? At the same time, new forests appear, with vegetation that also differs from that found today, and the temperatures rise. A meteor impact around 12,500 years ago may also have played a role in these changes. The big questions have always been of the chicken-and-egg kind. Take the demise of the megafauna and consider whether it was caused by a steady climate change accompanied by changes in vegetation or a killing of the animals by the humans who had recently arrived, followed by the changes in vegetation sketched above. From the analyses of several lake sediments in Indiana and New York it is clear that the animals disappeared a thousand years before the big changes in vegetation took place. This suggests that it was probably humans who killed the animals, and this was one reason for a change of vegetation and the fires. For the next thousands of years, Sporormiella spores are rare and hard to find. With the appearance of European settlers, European plants, and especially livestock, in the sixteenth and seventeenth centuries, the numbers of Sporormiella spores increase again – big herbivores are again plentiful in North America.
Sporormiella photo courtsey Alain Brissard
The oldest evidence of Sporormiella comes from the Yukon, which was part of the Beringian non-glaciated refugium during the Pleistocene and was buried under a thick layer of tephra from a volcanic eruption around 25.000 years ago. Various other fungal dung spores, found in the vegetation, resemble the spores of Sordaria and Podospora. The latter are huge and this alone makes them easy to recognize. Also from the Yukon comes a report of fungi in the coprolites (fossilized animal scat) of a ground squirrel that lived around 12,000 years ago. At that time the area is believed to have been an open tundra, grazed by woolly mammoths, Yukon wild ass, caribou, large-horned bison, now-extinct muskox, and also a large kind of mountain sheep. A complete nest of a ground squirrel was found and, in its dung, are fungal species that are specific for rodent scat. Sporormiella spores were also found in the colon of a mammoth preserved in the Siberian permafrost, and in several dung heaps found under the animal. For California there is one study of Exchequer Meadow in Fresno County which shows that Sporormiella spores are abundant in sediments that are older than 10,300 years; interestingly their numbers do not increase in the last few centuries.
New Zealand lacks land dwelling mammalian herbivores, nevertheless, the presence of Sporormiella spores in preserved bird droppings and dung, tracks the disappearance of several moa species, the arrival of European settlers and their animals, and the introduction of Red deer in the beginning of the 20th century. The moas were plant-eating, wingless birds that were extirpated by Maori hunters, before western colonization.
So, a few glimpses of the world in days past are provided not only by pollen and other plant remnants, but also by the spores of itty bitty dung fungi.
Some articles for further reading:
- Davis, O.K. 1987. Spores of the dung fungus Sporormiella: increased abundance in historic sediments and before Pleistocene megafaunal extinction. Quaternary Research 28: 290-294.
- Geel, B. van, G.D. Zazula & D.E. Schweger. 2007. Spores of coprophilous fungi from under the Dawson tephra (25,300 14C years BP), Yukon Territory, northwestern Canada. Palaeogeography, Palaeoclimatology, Palaeoecology 252: 481-485.
- Geel, B. van, J. Buurman, O. Brinkkemper, J. Schelvis, A. Aptroot, G. van Reenen & T. Hakbijl. 2003. Environmental reconstruction of a Roman Period settlement site in Uitgeest (The Netherlands), with special reference to coprophilous fungi. Journal of Archaeological Science 30: 873-883.
- Gill, J.L., J.W. Williams, S.T. Jackson, K.B. Lininger & G.S. Robinson. 2009. Pleistocene megafaunal collapse, novel plant communities, and enhanced fire regimes in North America. Science 326: 1100-1103. (also: Interview with Gill & Williams)
- Robinson, G.S., L.P. Burney & D.A. Burney. 2005. Landscape paleoecology and megafaunal extinction in southeastern New York State. Ecological Monographs 75: 295-315.
- Wood, J.R., J.M. Wilmshurst, T.H. Worthy & A. Cooper. 2011. Sporormiella as a proxy for non-mammalian herbivores in island ecosystems. Quarternary Science Reviews 30: 915-920.