Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
This is a painting of a Common Platanna, Xenopus laevis. I intended this for a children’s book about frogs. But anyways I’m sharing it here now! The name 'Platanna' is Afrikaans for 'Flat Anna', because these frogs have quite flat bodies. This helps them squeeze in under stones in ponds or riverbeds.
An alternative name for Platannas is 'Clawed Frogs'. It is unusual for amphibians to have claws, but these do, in the form of three rather short, blunt, blackish claws on each hind foot. The outer two toes on each foot don't have claws – on my picture you can only see one of the claws on the nearest foot, but two clawed toes on the other foot. The scientific name Xenopus means 'strange foot', referring to these claws. Platannas use the claws to tear large prey items apart.
Versatile Hunters and Scavengers
Platannas are quite common in South Africa – and other countries, about which I'll tell you more later. They are found in almost any kind of permanent or semi-permanent water. They are almost completely aquatic; they can absorb oxygen directly from the water through their skins but do occasionally gulp air at the surface. The only time they come entirely out of the water is during rains when they might leave ponds that are getting too crowded, squelching along overland until they luck on a new property.
I was delighted to stumble upon a large number of platannas once when I was perhaps ten or eleven years old or so. It was in a patch of 'veld' that is now a shopping mall and suburb. At that point they were just starting on the diggings for these new developments, and some water had collected in a small excavation, and there were perhaps thirty or more little platannas in the tiny pond. I went home and got a tin can, and then went back and collected about twenty of the platannas in my can. Catching them is fun and challenging … they are very agile and their soft, fat, slimy bodies slip through your fingers very easily. (Their species name laevis, means 'smooth'.) But I managed to fill my can and put a sieve over the top so they couldn't jump out as I carried them back home. At home I had a pond in which I'd tried to keep guppies, but those unfortunately had died over the winter. But platannas would be rugged enough since they survive outdoors all over the place. I released the platannas into the pond. Later on my dad and I made a much larger pond, and put in stones and some aquatic plants. The platannas lived there for a few years but eventually all left … there was perhaps something insufficient to the ponds we had made for them. But while they were there I could study them closely.
One thing I noticed is that the platannas could change in appearance based on the environment. The smaller pond was in the shade of trees, and there the platannas were darker and had conspicuous mottling on their bodies, as you can see in my picture. The larger pond was out in the sun, and the platannas living in it had lighter, plain brown, unmarked bodies. But they were all of the same original 'stock'. Perhaps this has something to do with camouflage, the mottling making them less visible in the dappled shade the trees cast over the small pond. They were all quite well camouflaged at any rate, blending in with the muddy pool bottoms and the stones.
You had to be somewhat careful to observe the platannas. They would mostly stay submerged, often hiding under flat stones. But sometimes they would float at the water surface, with their noses and nostrils protruding. They would sometimes crouch at the edge of the water. But if you approached too close too fast they would rapidly dive back down into the depths and kick up a cloud of mud to hide themselves in. With their muscular hind limbs, long toes and broad webbing between them, they can propel themselves very rapidly under the water.
In contrast to the muscular hindlimbs of platannas, their forelimbs are slender with finely pointed, unwebbed fingers. They don't use these for swimming at all, but for catching prey. Platannas will eat almost anything they can get … we fed them with various insects we caught in the garden, and dropped into their pond. If the insects were alive and struggled, the platannas would sense the ripples from their movements. They have lines of sensitive bumps, called lateral lines, running along the sides of their bodies. The lateral line can sense water movements and vibrations. Additionally, platannas have small tentacles below their eyes that probably also have a sensory function. With these sensors platannas detect the vibrations coming from their prey. If we dropped an insect in the pond that was dead and therefore not moving, we would prod it up and down with a finger or short stick, to create the waves for the platannas to sense.
When a platanna was hungry and sensed that there was something in the water, it would rise up from below, move in on the prey and grab it in its mouth. A platanna does not have a tongue, but catches its prey by opening its mouth wide, creating a 'sucking' effect, and grabbing the prey with its dexterous fingers and stuffing it into its mouth and down its throat. Prey that is very large can be manipulated so as to face the way that will make it go down easily; as I said, items too large to swallow whole can be fragmented using the back feet – they don't have teeth. A platanna that gets something very distasteful will spit it out again and rub at its mouth with its fingers. We found out that they don't like at all the 'miswurms' ('dung grubs'), the larvae of fruit-eating beetles, but they liked things like crickets and cockroaches. Platannas do have a good sense of smell, using that also for detecting their prey, but still they sometimes would go for something that they only discover to be foul tasting after actually getting it in their mouths.
I also strongly suspect that platannas will be cannibals if possible. In the large pond I left the platannas mostly to their own devices, because it having a large surface, a lot more insects would fall into it than in the small pond, and the platannas seemed to be doing fine. After neglecting them like this for many weeks I one day went and inspected it and found one very big platanna in it; it was about three or four times the size of the 'regular' ones, and there were far fewer 'regular' ones than before. I would not at all be surprised if it was eating the others, although I never actually saw this.
Yet another peculiarity of platannas is that they have no ear drums and external ears like most other frogs do. But they still have internal ears and can pick up sounds in the water. Their own calls are very unfrog-like, cricket-like clicks, creaks and buzzes that they make while fully submerged. They also don't have expandable vocal sacks like other frogs and toads, instead making these calls by contracting their throat muscles to vibrate special cartilage structures. The calls carry far in the water; the male calls to attract females, and the females call back to signal either their acceptance or refusal. Like other frogs and toads, mating consists of amplexus – the male grabbing the female around the armpits – and they will perform a kind of underwater 'mating dance' with rolls and loops. Finally she lays her eggs in underwater vegetation, and the male sheds his sperm over them.
From the eggs the tadpoles emerge. They are very easily recognized by the pair of long, straight tentacles they have at the front of their snouts. These can apparently sense movements as well as chemical signals. The tadpoles are semi-transparent as well, and typically hang in the water at an angle of about 45 degrees, with their heads pointing downwards. They metamorphose into tiny frogs, the hind legs forming first and then the front ones, the tail getting absorbed at last.
Platannas are now being bred in laboratories worldwide, and used for a great variety of scientific research. They are easy to keep and observe, and have so far revealed a lot about how organisms develop and how genes work, and have also been used for studies into the way nerves work, studies on poisons, and the chemical and electrical properties of cells and tissues . The first vertebrate animal to be cloned was a platanna, and they've also been on the space shuttle Endeavour, the goal being to see how animals grow and reproduce in the absence of felt gravity. Platannas were also used for pregnancy testing: exposure to the urine of pregnant women would cause female platannas to produce oocytes.
Because platannas are so widely bred in laboratories – and often kept as pets as well – and are so resilient and adaptable to boot, they've managed to establish themselves in many countries where previously they did not occur. They are now found in the southern USA, South America, Britain, Germany, The Netherlands and Ascension Island. Because they can travel from pond to pond, they can very rapidly colonize new areas and once they're out there it's almost impossible to eradicate them. Because they are voracious and eat anything, grow large (up to 5"/13 cm snout-to-vent length) and live for 20 or more years, they end up posing a serious threat to smaller frogs and to many kinds of fishes.
Perhaps a greater threat posed by escaped platannas is a kind of fungus that they carry, to which they are immune but which might decimate other amphibians, and might even be one of the causes of the current collapse of many amphibian populations worldwide.
An Ancient Lineage
The family the platanna belongs to, the Pipidae, is found today in sub-Saharan Africa and tropical South America. They most probably originated on the ancient southern continent, Gondwanaland. The oldest known fossils of them date back to 90 million years; Africa separated from South America at about 80 million years ago, and from then on the two lines have been evolving separately. The Surinam Toads of South America today have a build basically similar to that of the platannas and their other African relatives, but also a number of very weird features of their own. Fossils of other Pipids were also found in North Africa and the Middle East, where they are extinct today.