The frog that evolved to look like poo

To round off this month’s Naked Genetics, it’s time for quirks of evolution. And let me whisk you away to the tropical rainforests of western Indonesia...

Will - Look at this place. Beautiful isn’t it? Let's have a look around.

There’s an estimated 300,000 species of animal in Indonesia, that’s more than 4 times as many as in the UK. All of that life, all of those natural processes will inevitably lead to a lot of.. You know, waste. So, do keep your eye out for any excrement that might be around.

No, I’m serious. You need to keep your eye out. Otherwise today’s specimen has probably just bamboozled you.

Let us examine the curious case of Wallace's flying frog. The adult tree frogs are a delightful green and white, with big beady yellow eyes… and any normal programme trying to extol the virtues of this frog would absolutely focus on the adaptation in the animal’s name. Wallace’s flying frogs have such large feet with so much webbing in between their toes, that they can move from tree to tree by gliding. And that’s pretty magical. But Attenborough already covered flying tree frogs, so let's talk about something else.
Whilst the adults are a feast for the eyes, they are crucially green. That’s good news if you have many predators, and live in a rainforest. However, the juvenile frogs, having developed from being tadpoles, are red. That seems like a pretty bad idea in a green rich environment.

But, they aren’t just red. They’re red with brown and white speckles on them. And if you’ve ever returned to your car and found that a bird has left its business on your pride and joy, perhaps you can see where this is going. This remarkable amphibian has evolved a unique and ingenious camouflage strategy: it is the first vertebrate that we know of that evolves to resemble faecal matter.

Welcome back by the way to everyone that quickly went off to have a look at one.

And I’m sure you all agree, it’s pretty convincing. The mottled shades of brown and red. The coloration is not uniform but rather varies in texture and tone, mimicking the irregularities and inconsistencies found in…yeah. Additionally, the frogs often adopt a posture that enhances their resemblance to a lump of waste, by remaining motionless for long periods.

It was clearly convincing enough for scientists at the university of Vienna to put them to task. At the Schoenbrunn Zoo, wax replicates of frogs were placed into aviaries containing predatory birds. Some wax frogs were green, some completely red, and some had speckles like our dear old flying frogs. And whilst the red replicas were attacked significantly more than the green ones, that rate dropped by half when the red frogs had a ‘faecal flourish’ added to them.

So, the paper postulates, or maybe it poo-stulates. No it definitely doesn't. The paper postulates that, unsurprisingly, predators do not want to eat something that looks like poo.

And, whilst it’s a pretty gross theory, it’s not without precedent. There are a few other species, like the swallowtail butterfly caterpillar and the ‘bird dropping’ spider - no really- that really do make for excellent excrement. Biologically, a lot of species are hard wired to be repulsed by poo. And sure, it carries disease, or organisms that carry disease. Definitely something worth having, but at the same time, means there’s very little in the rainforest that wants to drop by some droppings on the off chance that it is a frog. It is simply not worth the risk, and I think that’s fair enough.