January 28, 2014

Why does the 3-toed sloth, unlike the 2-toed sloth, descend from its tree to defecate?

Why take the risk? The risk is only taken maybe once a week, but still: "The sloth is highly vulnerable on the ground and an easy prey for jaguars in the forest and for coyotes and feral dogs in the chocolate-producing cacao tree plantations that it has learned to colonize." The 2-toed sloth defecates from the tree, so why does the 3-toed sloth descend?

University of Wisconsin biologists find the key — which involves moths and algae — to this mystery.

32 comments:

CStanley said...

I got sidetracked thinking of the implications if the two-toed sloths defecating in the cacao trees.

Purpleslog said...

I would assume it is just good manners. I for one have never pooped outside while in a tree.

Tibore said...

So, if a tree gets shat on in the forest, does it make a sound?


... c'mon. You all knew someone was going to go there.

EMD said...

Your tax dollars hard at work?

traditionalguy said...

I have a feeling that three toed sloths do not make good house pets. But they do sort of resemble old white guy hoarders who descend into public to vote GOP every election.

gerry said...

I actually did poop from a tree when on a camping trip as a teen. The fork in the tree was just right, only four feet off the ground, and far enough from others to provide a little privacy.

And, come to think of it, it didn't make a sound.

David said...

Does a bear shit in the woods?

Of course.

Why does a bear shit in the woods?

Because it can.

lgv said...

Why do some people wipe themselves standing up? Turns out they never knew better.

Maybe 3-toed sloths never hang around with 2-toed sloths and realized they should be pooping from the tree. Maybe a 3-toed sloth was pooping on the ground when a 2-toed sloth turd hit me in the head and vowed it was just wrong to poop from trees.

YoungHegelian said...

Maybe because the 3 toed sloths discovered through the bitter, bitter process of natural selection just how angry a jaguar gets when you shit on its head from a tree.

Patrick said...

Whew! I was worried we'd never figure it out.

Naked Surfer said...

Cool science. I get the ecosystem hypothesis. Nifty.

I don’t get the reasons why there’s a difference in behaviors between the two and three-toed sloths as a matter of their fitness landscapes. Something went right over my head there. And thank goodness. I’m not saying the difference is reducible to learned behaviors, as if sloths were reading different copies of my favorite book, How to Shit in the Woods (just watch Althouse put up an Amazon portal link to this).

It’s just that I don’t get the biological reasons for the difference. Maybe need to skip the breezy NYT article and go straight to the sources at U of Wisconsin?

Ron said...

This whole post is an indirect reference to the SOTU tonight, correct? Something about the three branches(!) of government? Yeah, I thought so...

madAsHell said...

Two or three toes.

Is it a life style choice, or is it an expression of their genes?

Sorun said...

Everything is shitty in Scott Walker's Wisconsin.

gerry said...

This whole post is an indirect reference to the SOTU tonight, correct? Something about the three branches(!) of government? Yeah, I thought so...

So, a three-branch government descends to the ground before it shits, but one like they have in Great Britain (face it, the House of Lords is a sham) shits while aloft?

Cool beans.

gerry said...

Does a bear shit in the woods?

More importantly, if a bear shits in the woods and no one is there to hear it, does it still fart?

St. George said...

Our delicious friend the avocado exists today because it co-evolved with the giant ground sloth, a creature so beastly big that the avocado's pit could slide through its bowels and be deposited hither and yon.

Imagine a creature feasting on avocados, standing on its hind legs to devour them from trees. A Volkswagen on legs.

lge said...

I remember an old joke, the punch-line of which is, "I wish I had your problems, teacher."

I wish I had the problems of these differential-toe-numbered-sloth-crapping-habits investigators.

lge said...

Crapping on the ground is considered more genteel. The 3-toed sloth is a social climber, as well as a tree-climber.

And as Judge Roy Bean says, "That's my ruling."

lemondog said...

Your tax dollars hard at work?

Defecating sloths and the life/death of water drops, what more is there to know?

re: tax $$$$, its only paper.

Out of the mud grows the lotus.

Fritz said...

A great week to leave Wisconsin and visit South or Central America.

John said...

The next time someone asks me the type of question I might answer "Does a bear shit in the woods" I will say instead:

"Does a sloth shit in a tree?"

How is that for sneakily ambiguous?

I am going to Ecuador the end of February for 2 weeks. If I get a chance to do any touristing, I look up some sloths.

John Henry

John Henry

roger said...

This is not difficult. Given the lubricity and absolute value of the viscosity of your average sloth shit, the three toed sloth, with the opposing toe (thumb) has the distinct advantage on shit smeared branches and would naturally be more inclined to descend to the ground for defecation purposes.

Think, people, think.

sean said...

This doesn't work, intellectually. (Typical of the bankruptcy of most evolutionary biology.) An individual sloth would be better off remaining in the tree, even if thereby it ceased to do its part for the sloth/moth/algae/feces ecosystem. The other sloths would pick up the slack, ecologically, and the freeloader sloth would have superior reproductive fitness. Natural selection cannot favor a trait which disadvantages the individual organism, even if it advantages the species.

Dr Weevil said...

I'm pretty sure "differential-toe-numbered-sloth-crapping-habits investigators" could be a single word in German, though with just about as many syllables.

Terry said...

"And that's how the tiger got its stripes!"
This is a "just-so" story. The sloth 'decides' to go to the ground to defecate so the moths can lay eggs in its feces? This is crappy science in every sense of the word 'crappy'. How do we know that the moths haven't 'decided' to lay their eggs in the sloth feces because the sloths choose to deposit them on the ground?
From the article: "Why then does the sloth take such a risk every week? Researchers who first drew attention to this puzzle in 1978 suggested that the sloth was seeking to fertilize its favorite tree."
Modern science considers this idea a product of the ignorant past. The modern idea has been peer-reviewed and so is indisputable Truth.

Revenant said...

The other sloths would pick up the slack, ecologically, and the freeloader sloth would have superior reproductive fitness.

A gene that only provides a benefit if most of the population *doesn't* have it (your "free rider" scenario) has no long-term viability. There is a negative feedback loop in play -- each generation is less reproductively successful than the one before it, because in each generation the percentage of "non-free-riders" drops. This is a recipe for species extinction.

The genes that thrive are ones that either benefit from being widespread, or at least do no harm when widespread -- ones that benefit from a positive feedback loop.

Also, you are incorrect in believing that a gene has to benefit its own carrier in order to be selected for. What matters is whether or not the gene is passed on, not whether or not it is passed on by you in particular. That's how beehives work -- 99.99% of bees never have any kids at all and live their lives solely to allow that fertile 0.01% their share their genes with (the queen) to thrive and reproduce.

Revenant said...

This is a "just-so" story. The sloth 'decides' to go to the ground to defecate so the moths can lay eggs in its feces?

"Sloths decide to come down in order to help moths" is not the right way to put it. They're sloths. They don't "decide" anything. You're just confused because the NYT dumbed down the story. You might have noticed that there are no actual *quotes* in it.

The discovery here is that there is indeed an advantage (for this particular species) to opting to defecate on the ground rather than in the trees.

Evolutionary theory predicts that if you see a species instinctively routinely engaging in seemingly-harmful behavior, you will find that there is a benefit to its doing so. This is a prediction that has been empirically confirmed across many thousands of species, so it has a pretty good track record.

Three-toed sloths' bathroom habits seemed anomalous, as scientists couldn't identify any benefit to risking death-by-jaguar. It turns out there IS a benefit, albeit indirectly. So, no more anomaly.

Rusty said...

Blogger Purpleslog said...
I would assume it is just good manners. I for one have never pooped outside while in a tree.


It's liberating.

Old RPM Daddy said...

Okay, nobody's posted a darling sloth video yet, so I guess I'd better do it.

Crimso said...

"If I get a chance to do any touristing, I look up some sloths."

I really don't think that's a good idea. Consider what might be incoming as you look up...

[My first attempt at typing this came out as "as you loo up." And that's no shit.]

Linda Hinkel said...

I was curious about why a sloth would come down to defecate too and once looked it up. I can't remember the exact theory but I think the fact that the 3 toed sloth is actually fertilizing the tree they live in (by going to the ground and ensuring that their feces fertilizes their tree rather than get washed away to other parts of the forest) was the advantage and since 3 toed sloths are herbivores and more dependent on the tree they live in for their nutrients (where as 2 toed sloths are omnivorous and faster moving, allowing them to gather nutrients from other sources), it kind of makes sense to farm and care for the tree in which they live.