Monday 1 August 2016

African Clawed Frog

Image: Brian Gratwicke
When you see the unconventionally cute face of an African Clawed Frog, you'd be hard-pressed to imagine you were looking into the beady eyes of a ravenous, meat-eating beast.

Then again, I always find it difficult to imagine frogs and toads as ravenous, meat-eating beasts. Surely they're far too silly-looking for such shenanigans? Surely ravenous, meat-eating beasts are lean, muscular and athletic, with enormous claws and even bigger teeth.

Image: Josh More
On the other hand, the entire reason WHY ravenous, meat-eating frogs are so silly-looking is that they're little more than a giant mouth and a giant gut on legs. If Pac-Man had to walk, he'd be a toad. Maybe that should be something of a clue?

African Clawed Frogs differ from most other frogs in that they're sort of squished flat. They're like a more podgy, less angular version of the Surinam Toad. And that makes sense since they both belong to the Pipidae family, alongside several other weird, squished-up frogs.

Image: H. Krisp
Xenopus laevis
There are about 20 species of African Clawed Frog, all from sub-Saharan Africa.

Large, widespread species like Xenopus laevis (often called, quite simply, the African Clawed Frog) can reach 13 cm (5 inches) long and are found from Nigeria all the way down to South Africa.

Image: Václav Gvoždík
Lake Oku Clawed Frog
On the other side of the scale, both in terms of size and range, is the Lake Oku Clawed Frog (Xenopus longipes). These guys reach more or less 3 cm (1.2 in) long and are found only in a single lake in Cameroon. That lake is an old, water-filled volcanic crater, 2,000 metres (7,000 ft) up Mount Oku. It's ever so mystical. I'm sure they have an ancient African Clawed Monastery or something up there. Maybe they practise African Clawed Martial Arts.

Almost all African Clawed Frogs belong to a single genus called Xenopus, which means 'strange foot'. So what's so strange about their feet?

Well, they are huge. That's pretty odd. African Clawed Frogs are basically entirely aquatic, only climbing onto land when they need to find a new pond or slow-moving river to hang out in. Some species can even burrow underground during droughts and snooze for several months until the rains come back.

They'd rather not do that, though. They'd much rather kick their enormous, webbed, hind feet and swim with surprising power and agility. That's the kind of thing you can do when you're not too toadishly spherical.

Image: Brian Gratwicke
However, the really strange thing about those hind feet is that three of the toes each end in a small, black claw. What might those be for? Apparently they're mostly for tearing things limb from limb, fin from fin, or 'to ribbons.' Or at the very least to bite-sized chunks.

The thing about African Clawed Frogs is, squished flattish as they may be, they're still complete guzzle-guts. They will feed on absolutely anything, so long as it's meat. Worms, crustaceans and other bottom dwelling invertebrates are the mainstay of their diet but they'll also chomp on any fish or even bird too slow or too unlucky to escape. And they're not above scavenging carrion, either.

African Claws Frogs have a good sense of smell, sensitive fingers and small, upward-facing eyes which are lidless like those of a fish. And, like a fish, they have a lateral line. It's a sort of groove full of hairs, and it's extremely sensitive to movement in water. They're a lot like ears, only aquatic. In African Clawed Frogs it looks like a line of stitches so bad you'd think you were looking at Dr. Frankenstein's early experiments.

That's about all they need to find their prey. If it's small enough, they'll eat it in a gulp. A little bigger and they'll gobble it up, using their small, front legs to cram it into their mouth. It's not pretty, but the act of ravenous meat-eating seldom is. And if their prey is bigger still, our African Clawed Frog can grab it with its mouth, and then kick it with its clawed feet. And those feet are just as enormous and powerful as they were when they were kicking water.

Video: articmth

With that unpleasantness over (for the time being), it's time for some fun. African Clawed Frogs have no vocal sac, so the male's call to the females is a kind of maddening chirp as you might hear from a electric cricket running low on power. In some species the female will actually make an approach and call out to a male to ask him if he'd "like to come round for some coffee and by the way I'm just about to lay some eggs."

She can lay hundreds or thousands of eggs; the tadpoles will normally take several months to metamorphose into adults. You can tell an African Clawed Tadpole because it grows a moustache at an early age. They're barbels really, like on a catfish, but it still looks weird. Especially when they start growing legs.

Image: Václav Gvoždík
Fraser's Clawed Frog (X. fraseri)
But this is not their only experience of the wonders of sexual reproduction. Indeed, African Clawed Frogs have enjoyed a long and illustrious career in science. Maybe not all that illustrious. Worthwhile, at least. Possibly not 'enjoyed', either.

It began in the 1930's, when X. laevis (the common, widespread one called simply the African Clawed Frog) was used as a pregnancy test. Grab a female frog, inject her with urine, and if the frog lays eggs within the next 24 hours, then whoever's urine that was is pregnant. It's all to do with hormones, you see.

Image: Brian Gratwicke
Cameroon Clawed Frog (X. tropicalis); sometimes placed in a genus called Silurana
Before using a frog they tried it out on mice and rabbits, but then they had to kill the mouse or rabbit and perform an autopsy to see the test results. With frogs, no-one had to die and the same frog could do more than one test. Thus, this lowly entrance of the African Clawed Frog into the world of science went on into the 1950's before other tests were developed that didn't involve animals.

Since then, African Clawed Science has really flourished. X. laevis and their smaller cousins X. tropicalis have become model organisms, with interests in embryology, toxicology and molecular biology amongst others. Along the way they've been cloned, launched into space and had their genome sequenced.

Image: Václav Gvoždík
Tropical Clawed Frog (X. tropicalis) also sometimes placed in Silurana
African Clawed Frogs are hardy creatures with simple needs. They're easy to keep and easy to feed. That's part of why they're so popular among scientists who'd much rather be peering through a microscope than looking for a delicious, birthday treat for Betsy the Frog. People who keep pets often like that sort of thing, too, and so African Clawed Frogs can be found in aquariums all over the world. Unfortunately they sometimes escape or get let loose, which is when their hardiness and ravenous meat-eating can become quite the problem.

Today, they're not just found in sub-Saharan Africa. They're also found living wild and free in the United States, the UK, Germany, the Netherlands and more. They're doing quite well for themselves. And they don't seem to mind foreign food.

Image: Josh More
Even worse, they appear to be unaffected by chytridiomycosis, the terrible fungal disease killing frogs all over the world. They can still carry the actual fungus, they just don't seem to catch the disease, which means they're really good at spreading it.

Dear, oh dear. Maybe those guys in Lake Oku had it right along. Just find a nice dormant volcano to relax in and let the world sort itself out.


TexWisGirl said...

rather cute ravenous ones.

elfinelvin said...

Frogs simply should not be flat. They should be pudgy. The claws do make up a bit for the flatness. Wicked claws! :)

Lear's Fool said...

That was the least efficient fish capture I've ever seen!

No wonder they're not fat.

Joseph JG said...

@TexWisGirl: No doubt!

@elfinelvin: Aside from deep sea fish, frogs have got to be the most uniformly SOFT thing with a backbone. It's nice to see them pull out something a little more solid once in a while!

@Lear's Fool: Getting eaten alive by an inefficient eater has got to be the worst!

Lear's Fool said...

@Joseph That's positively embarrassing, isn't it?

Like getting eaten by nearsighted Koala who thought you were a eucalyptus leaf.