10 crazy frogs

I’m guessing that many Lost in Science readers and listeners could do with some cheering up at the moment, and there’s nothing that does the job like outrageous amphibians.

The following are ten facts about frogs – and toads – that will at the very least give you something else to shake your head about.

1. Frogs that hear with their mouths

This is actually the science news that inspired this post: the Gardiner’s Seychelle frog, Sechellophryne gardineri, a frog so small that it doesn’t have ears (I know, I never thought about frogs having ears either).

Diagram showing how the Gardiner's Seychelle frog's mouth amplifies the sound of its call and delivers it to the inner ear (click to embiggen)
Diagram showing how the Gardiner’s Seychelle frog hears with its mouth. 99.9% of all sound is reflected off its skin, but the frog’s own call resonates in its mouth (Image by R. Boistel/CNRS)

Only about one centimetre long, the Gardiner’s Seychelle frog doesn’t have room in its tiny head for all the intricate machinery of middle ear bones. Instead, its mouth acts as a resonant cavity tuned to the frequency of its call, which then transmits the sound to the inner ear.

(Boistel R, Aubin T, Cloetens P, Peyrin F, Scotti T, Herzog P, Gerlach J, Pollet N & Aubry J-F 2013, “How minute sooglossid frogs hear without a middle ear”, Proceedings of the National Academy of Sciences, published online 3 September 2013, doi: 10.1073/pnas.1302218110.)

2. Wolverine frog, with hair and retractable claws

Actually known as the hairy or horror frog, Trichobatrachus robustus comes from Cameroon in central Africa. The males have long, thin growths on their skin that look like hairs but are probably more like gills for breathing.

Hairy frog, Trichobatrachus robustus (click to embiggen)
Trichobatrachus robustus, showing its horrid hair, but not its terrifying claws (Photo by Gustavocarra, via Wikimedia Commons
But most startling is that when threatened – or picked up by a human handler – the hairy frog intentionally breaks the bones in its toes and forces them through its skin like claws. And because frogs are good at regenerating, it’s believed to slowly heal over when it relaxes.

3. Frog that keeps its babies in its stomach and comes back from the dead

Well, it hasn’t quite come back from the dead yet – Australia’s gastric-brooding frog, Rheobatrachus silus, became extinct in 1983. But while they were alive, female gastric-brooding frogs swallowed their fertilised eggs and stopped eating while they incubated. After about a week they gave birth to baby frogs – not tadpoles – through their mouths.

The extinct gastric-brooding frog, giving birth through its mouth (click to embiggen)
The extinct gastric-brooding frog, giving birth through its mouth (Photo by Mike Tyler)

If you think that sounds complicated, it’s even trickier now they’re extinct. But Professor Mike Archer and his team from the University of NSW have succeeded in cloning frozen tissue, producing living embryos. Yes, just like in Jurassic Park.

(We spoke to Professor Archer on 4 April 2013 – you can listen to the podcast.)

Click through to the next page for the remaining 7 frogs on our list.

4. Flat toad that gives birth through its back

So it gets weirder: the South American Surinam toad, Pipa pipa, is the world’s flattest amphibian. Adults are 12-20 cm long, but only about 2 cm thick.

Surinam toad hiding under logs in an aquarium (click to embiggen)
Surinam toad at the Steinhart aquarium in San Francisco (Photo by Stan Shebs, via Wikimedia Commons)
Despite this, they insist on filling that flatness with passengers. The female lays her eggs on the male’s belly, who then fertilises them and rolls them into pockets on the female’s back. There, they incubate and erupt as fully-formed tiny froglets. It’s so disgusting it gets a second photo:

Tiny froglets emerging from the back of a Surinam toad (click to engrossen)
Eww, gross! (Photo by Endeneon, via Wikimedia Commons)
5. Toads that predict earthquakes

Remember last year when Italian scientists were convicted for failing to predict the earthquake in the town of l’Aquila? And the scientific community was up in arms because predicting earthquakes is basically impossible?

Well, it turns out that toads can predict earthquakes. In fact, any old toad. Zoologist Rachel Grant was studying a breeding colony of common toads, Bufo bufo, near l’Aquila, and noticed that they stopped spawning and abandoned their pond 5 days before the quake struck.

Common toad jumping (click to embiggen)
Basically if you see this, run (Photo by N p holmes, via Wikimedia Commons)
It’s possible that they responded to chemical changes in the groundwater – or perhaps witches were onto something by having toads as familiars.

(Grant RA & Halliday T 2010, “Predicting the unpredictable; evidence of pre-seismic anticipatory behaviour in the common toad”, Journal of Zoology, Vol. 281, no. 4, pp. 263–271, DOI: 10.1111/j.1469-7998.2010.00700.x.)

6. Flying frogs

Yes, yes, there are species like Wallace’s flying frog, Rhacophorus nigropalmatus, but it glides rather than flies, using its enormous webbed feet.

No, I’m talking about levitation, of the kind that won Michael Berry and Andre Geim an IgNobel prize. You see, water is diamagnetic, meaning it’s repelled by a magnetic field. Berry and Geim decided that a spectacular way to demonstrate that was by levitating a frog, seeing as frogs are largely water (as are you).

Geim later went on to win an actual Nobel Prize for his work on graphene, which itself was a rather simple demonstration you can do at home. No giant magnets required.

(Berry MV & Geim AK 1997, “Of flying frogs and levitrons”, European Journal of Physics, no. 18, pp. 307-313 [PDF 223 KB].)

7. Vomiting their whole stomach

Maybe you liked that last video, maybe you found it disturbing. Well, the next one leaves no doubt.

Apparently, when a frog eats something bad it doesn’t muck around. It throws up its whole stomach, cleans it out with its forelegs, and then swallows it back down. If you don’t believe me, watch the video.

The internet tells me that this ability was discovered on a space mission. But then, the internet says a lot of things.

8. Frozen frogs

OK, one more video: the North American wood frog, Rana sylvatica, hibernates over the winter in freezing conditions.

Its tissues accumulate urea and convert glycogen into glucose, basically filling its cells with sugar and preventing ice crystals forming.

The wood frog takes about 40-50 minutes to thaw and come back to life, and can freeze again multiple times in a season without croaking. Quite literally.

9. Desert-dwelling water hoarders

For another extreme survival technique, it’s back to Australia and the water-holding frog, Litoria platycephala. This clever critter lives in arid areas, and can survive 3-6 months buried underground in a watertight cocoon fashioned from its own skin.

Water holding frog in its cocoon
Water-holding frog in its cocoon (Museum WA)

It emerges when it rains, laying huge clutches of up to 500 eggs, then goes back to hibernation.

Some people believe the water-holding frog inspired the legend of Tiddalik, a frog that drank all the world’s water until it was made to laugh. It’s also believed to have been an emergency water supply for Australian Aboriginal people.

10. All incredible endangered frogs

This one’s a copout: Australia and indeed the world is full of weird and wonderful amphibians, many of which are endangered. One of the chief culprits is the chytrid fungus, Batrachochytrium dendrobatidis, which infects their skin and is killing off frogs worldwide.

An example is the Baw Baw frog, Philoria frosti, one of the stars of Zoos Victoria’s conservation program. Only about 5 cm long, this frog is only found on the Mt Baw Baw plateau in Victoria. It lays its eggs in nests beneath wet moss, where the tadpoles don’t swim but instead feed on their own yolk sacks.

Baw Baw frog on its bed of sphagnum moss
Baw Baw frog on its bed of sphagnum moss (Photo Claire Kelly, via Zoos Victoria)

Of course, by occupying such a specific niche the Baw Baw frog is also exceedingly vulnerable to climate change. So find out more about the Baw Baw frog and its relatives while you can.

(More Australian frogs and recordings of their calls can be found in the Museum Victoria Field Guide App.)

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