Further investigation into wombats’ unique droppings has revealed a general law of mammalian feces, determining why some animals produce pellets while others make logs – and the work could even have some surprising applications.
Among the many features that make wombats wonderful are their droppings, which are so cubic you could almost use them to play board games if you’re not too germophobic. The sharp sides of the feces make them easy to identify for Australian bushwalkers, but have prompted many to wonder whether defecation is not a painful process for the tough marsupials.
Dr Scott Carver of the University of Tasmania attracted more fame for his part in discovering that these shapes are made internally by the wombat intestine, not the anus, than for any of his hundreds of other scientific papers. Now Carver and co-authors are back with a paper explaining why the droppings are so regularly sized, rather than sharp-sided rectangular prisms.
Wombats are the only animal known to produce poo like this, Carver told IFLScience, “Although some kangaroos do produce feces with one or two flat sides.”
It is thought the evolutionary benefit that justifies the discomfort is the use of droppings as a signaling method, perhaps to tell other wombats a burrow is occupied or report on their reproductive health. As Carver proved in his previous work, square-sided droppings are less likely to roll away, giving them olfactory staying power in hilly country.
However, oblong shapes would also be unlikely to roll well, so why the smaller pellets? Carver and co-authors were inspired by the regular hexagonal rock formations seen at Ireland’s Giant's Causeway and some other volcanic sites. These have been explained by cracking induced by rapid cooling at the surface of the lava, while the stone-to-be remains hot inside.
Wombat intestines are not similarly molten, but the team suspected the drying process performs an equivalent role. After experiments involving corn flour in troughs blasted by heat lamps, the authors found the shape of poo is dictated by its moisture content within the intestine. Animals with less than 70 percent moisture in their feces produce pellets, which Carver defined as “length being not more than twice the width”.
Above this boundary, droppings will be longer. Humans tend to average 75 percent moisture, Carver noted – although as the Bristol Stool Chart demonstrates, there is wide variation. When the moisture is even higher, such as in 85-90 percent liquid cow pats, the product is a sloppy puddle.
Work like this attracts online denunciations of wasted money, but Carver told IFLScience; “It was done with almost no funding. We all donated our time.” He didn’t even need to trade in the ten trillion Zimbabwean dollar note Carver won with his 2019 IgNobel prize for the earlier part of the research.
Yet cheap as the work has been, it could prove surprisingly valuable. For one thing, a better understanding of poo permutations may eventually improve our capacity to identify colorectal cancer or other diseases of the gut.
Moreover, Carver told IFLScience that “Our earlier work identified a way to produce cube shapes in a soft tube for the first time. That’s not going to lead to a manufacturing revolution, but it might help if we need to coax delicate materials into certain shapes.”
Meanwhile, Carver has a student testing the hypothesis wombats use their poo to communicate. This will be done by moving cubes between territories and watching how individuals respond to the arrival of strange smells.
The work is published in the journal Soft Materials
[H/T ABC Tasmania]