There comes a moment in every biology blogger’s life when he or she must write about poop.
This is one of those moments.
When a paper’s title includes phrase, “fecal particle size,” sometimes, one just thinks, “Okay, I really should read that, if for no other reason than it was clearly a lot of unpleasant work for someone.”
The intellectual issue here relates to the difference digestive strategies of mammals and reptiles. Mammals chew; reptiles generally don’t. This has a lot of consequences. It means mammals can spend a lot less time digesting food. This, in turn, helps to make the high-energy endothermic lifestyle that mammals enjoy possible. And it means that mammals should have feces that are more... fine-grained, if you will. You’re not likely to find something like this in the droppings of a mammal:
The authors recovered this particular leaf from the feces of a common iguana.
But this is science, damnit, not a schoolkid’s joke! We need quantifiable data on the particles in poop! We need to test those turds!
So, Julia Fritz and her four co-authors collected a lot of samples from fourteen reptiles species held in European zoos. Then, they started sieving all those feces. They had a few predictions about what they’d find. The major one, that the reptiles’ feces would have large particles, was confirmed. They had also predicted that large bodied animals would also tend to have coarser feces, probably due to bite size.
They also predicted that animals fed prepared food would tend to have larger particles, reasoning that those feeding on plants in the ground would be able to manipulate the plant in ways that allowed the reptiles a chance to regulate the size of the bites they took. They tested two tortoise species, and found the effect in one, but not the other. So the story is a little equivocal here.
Now, you may think that you’ve heard about reptiles using stones in their stomach to break down their food. Fritz and company find no evidence of that at all. It’s a little surprising, as I would have thought this would be something that would have been settled long ago.
As an outsider to the digestive physiology field, it’s a bit difficult for me to figure out what the next logical set of questions to ask is. The authors, however, say that one thing they would like to do is get a lot of excrement from free-ranging reptiles. They modestly note that this is “a major logistical challenge.”
Fritz, J., Hummel, J., Kienzle, E., Streich, W., & Clauss, M. (2010). To chew or not to chew: fecal particle size in herbivorous reptiles and mammals. Journal of Experimental Zoology Part A: Ecological Genetics and Physiology. DOI: 10.1002/jez.629