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Column: Things of Nature and the Nature of Things

Things of nature

Pregnancy, frogs, diamonds and Barrydale – what’s the connection?

by Les Minter

When Linnaeus introduced his new binomial system for naming animals and plants in 1758, he referred to amphibians as “foul and loathsome animals”. Granted, they are rather cold and clammy when handled, but do they really deserve such bad publicity?  Apparently not. 

Karoo Art Hotel

Take the common Platanna, for example. Named Xenopus laevis because of its unusual clawed toes and smooth skin, this frog is widespread and abundant in southern Africa, and can be found in almost any garden pond or farm dam in the Little Karoo. It is a voracious predator and scavenger, easy to breed in captivity and a popular fishing bait.

Xenopus laevis / Platanna

Platannas are entirely aquatic and seldom seen on land. They even call underwater to attract a mate! The glassy, transparent tadpoles filter algae and other plankton out of the water and maintain their position by wiggling the tips of their tapering tails. Schools of tadpoles, with their large, square heads and gaping, toothless mouths, hang motionless in the water like pods of tiny whales.

The diamond connection:

Platannas belong to an ancient family, with a pedigree stretching back to the era of the Dinosaurs. In the late 1970’s, when de Beers were prospecting for diamonds near Marydale, Northern Cape, several well-preserved frog fossils were found in sediments deposited during the Late Cretaceous (66-100 million years ago). The kimberlite pipes that bring diamonds to the surface, originate in the Earth’s mantle at depths of 150-450km. They erupt rapidly and violently, accompanied by a lot of gas, mainly CO2. The frogs had been living in the crater lake of one such extinct volcano, and it is speculated that they died during a “degassing event” (it seems Gaia also suffers from flatulence). One of these fossils, an ancestor of the Platanna, was described in 2005 and named Vulcanobatrachus mandelae.


The pregnancy surprise:

When Lancelot Hogben became Professor of Zoology at UCT in 1927, he and his students began to investigate the effect, on platannas, of a hormone, hCG, found in the urine of pregnant women. To their delight they found that when this urine was injected under the skin of a female platanna, the frog would, without fail, produce a batch of eggs within 5-12 hours. The first pregnancy tests, developed during the 1920’s, were carried out on mice and rabbits, but took longer, and the animals had to be killed so that their ovaries could be examined. Platannas were not adversely affected by the procedure and could be re-used, surviving up to 30 years in captivity. Thus the Hogben Test soon replaced the others and between 1940 and 1960 tens of thousands of frogs were providing answers to the question uppermost in the minds of an equal number of women around the world. 


Reminds me of that song ….. how did it go ….. 

Hello muddah, hello faddah, 

What you doing to, that poor padda? 

If he answers, your big question,

Will you let him go so I can take him fishin?

The Barrydale connection:

Enter Clive MacDonald, veteran veterinarian, now living in Barrydale. Between 1974 and 2001, one of Clive’s clients was John Wood, owner of the South African Snake Farm in Sunnydale, who made a living by collecting snake venom used to produce antivenom, and Platannas used in teaching and medical research. The Platannas, captured in the vicinity of Paarl and Stellenbosch, were delivered to Clive’s Practice in 44-gallon drums, each containing about 400 frogs. After checking each consignment for signs of injury or fungal disease, Clive would issue the clearance certificate required for export. The frogs would then be dispatched to medical laboratories, research institutions and universities all over the world. The Cape Provincial Administration’s Nature Conservation Department also reared Platannas for export at their Jonkershoek and Pirie fish hatcheries. Between 1941 and 1969, they exported 400 000 Platannas to 104 global destinations! By this time Xenopus laevis was the world’s most widely distributed amphibian.

During the mid-1960’s chemical tests began to replace the Hogben test, but by then the Platanna was firmly established as an experimental animal in many areas of research, such as developmental biology, physiology, cytology and embryology. It has been used for biological research in space for over 40 years and was the first vertebrate species to be cloned. Its skin contains antibiotic compounds called Magainins, that are active against bacteria, viruses and fungi and appear to be less susceptible to acquired microbial resistance. 

Not bad for a little padda that lives in your fishpond, don’t you think!

*Les Minter is a retired herpetologist and is therefore someone with friends in low places.

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About the author

Mickey Mentz

From my Barrydale base, my goal is to tell the stories of people and places on the picturesque R62. Ek het oor die jare 'n cappuccino verslawing ontwikkel en my honde se name is Bella en Obi.

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