Creature Feature: The frog that soared into orbit

Family: Pipidae
Genus: Xenopus
Species: Xenopus laevis (African clawed frog)
Most often confused with: African dwarf frog
Distribution: Naturally occurring in southern Africa, introduced worldwide.

In the quiet, warm waters of lakes and ponds throughout southern Africa lives a very unusual amphibian. Grouped within the family Pipidae, all of whose members are wholly aquatic and tongueless (toothless too!), the African clawed frog (Xenopus laevis), or platanna, possesses a number of exceptional characteristics. With its wedge-shaped, flattened body, tiny upward-gazing eyes and no visible eardrums, it could easily be mistaken for a soggy pancake. (Click here to see a cool 3D animation of the complete Xenopus laevis skeleton).

Xenopus laevis is perhaps the best known of the 14 species in the genus, and it’s not hard to see why. Few species better exemplify the notion that nature is loathe to mess with a successful adaptation. The term Xenopus is Latin for “peculiar foot”,  which rather aptly describes the platanna’s enormous webbed, five-toed, three-clawed rear feet. Since it has no tongue, the platanna uses its front toes as fingers to bring food to its mouth. And things get even stranger. Aquatic by nature, Xenopus laevis spends most of its time in thick mud – even though it has fully developed lungs! So, not only are its clawed feet essential for eating, but they’re a vital design feature for swimming up and down whenever the frog needs a breath of fresh air (which is often). During the drier months of the year, its front claws, with their thickened fingertips, perform a third important function as burrowing tools when plantannas dig themselves a hibernation hole under the mud, where they sleep for many months until the rains return.

Take me to your leader! (Image via Kuribo, Creative Commons)

GIANT LEAPS OF THE FROG KIND

Platannas endured what I can only describe as “a series of unfortunate events” thanks to humankind’s quest for knowledge. In the 1930s and 40s, live female Xenopus frogs were used to develop a kind of amphibian-based pregnancy test for women (when female frogs were injected with a pregnant woman’s urine they would produce eggs within 48 hours thanks to their ability to detect HCG, a hormone that women produce during pregnancy). Thousands of frogs were exported for this purpose from Africa each year, possibly carrying a deadly amphibian fungus with them (a disease that has since spread across the world and is now a major cause of frog and toad decline).

African clawed frogs were also the first vertebrates to be successfully cloned and in 1992 several specimens made history by being the first amphibians sent into orbit. On one particular space mission, researchers discovered the rather unsavory way platannas rid themselves of poisons: by literally throwing up EVERYTHING. First, the entire stomach is ‘thrown up’ (so it’s literally dangling out of the mouth). Then, using its forearms, the frog digs out all of the stomach contents and then swallows the stomach back down again.

PETER PAN SYNDROME
Many tadpoles of the African clawed frog never grow up (a condition known as neoteny). Instead of developing into adults, they become giant, grossly deformed tadpoles with hunchbacks (Potential Prince Charmings? I think not).

Interested in other phenomenal frog adaptations? Watch this camouflaged male foam nest frog (Chiromantis xerampelina) awaiting nightfall to call for females. Cameraman Boris van Schoenebeck explains how the female frogs create a frothy nest of protection for their eggs.