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www.thevillagenews.co.za
3 February 2021
MY ENVIRONMENT
These are a few of my favourite… frogs By Dr Anina Lee
itats and no understanding of ecosystems. Sometimes I still wonder… Another of my local favourites is the Drewes’s Moss Frog that hangs out in the Kleinrivier Mountains. Their trilling call can be heard along permanent seeps both day and night during their breeding season from June to October.
T
he last 20 years of my life have been an adventure in nature filled with delight. Working for Whale Coast Conservation (WCC) and being a member of the Hermanus Bird Club and Hermanus Botanical Society has allowed me to explore so many fascinating aspects of our local biodiversity. Tagging along with my colleague Sheraine van Wyk has allowed me to learn about chameleons and frogs and then share the privilege of that knowledge through the WCC Youth Environment Programme and our guided walks in nature. I want to tell you about some frogs I have met in my life. One of my favourites is the small Arum Lily Frog – such a delicate cream with orange legs, usually hidden under its body, and with a loud screechy mating call quite out of proportion to its delicate frame and looks. The Western Leopard Toad is an awesome frog – so large and colourful, and sadly, so endangered. Their habitat along the coast from Cape Town to Agulhas has systematically been destroyed under the guise of “development”. Wetlands, such as those in Betty’s Bay, have been drained with the blessing of local government. In the days when these coastal areas were developed, there were no environmental laws that protected wildlife hab-
They are so tiny (the size of a thumbnail) and so well camouflaged that in the five years I have been listening for their mating calls in order to estimate their numbers in Fernkloof, I have not seen a single specimen “in the flesh”. This little frog depends on year-long damp places staying damp. It breeds in the moist undergrowth, laying eggs that develop into tadpoles and metamorphose into froglets, all still in the soggy undergrowth. Three years of hot, dry summers from 2017 to 2019 took an enormous toll on their numbers. Despite being in a protected environment, they have no defences against climate change. However, I retain a very soft spot for a frog I encountered years ago in a different world as a graduate student. The research focus of the laboratory was on how animals adapt to drought. Animals like frogs can bury themselves when ponds dry up and stay in a state of dormancy (called aestivation) for up to
a year or more, until the next heavy rains. The familiar ‘platanna’ (Xenopus laevis) is an excellent example of this useful adaptation.
were a deep green colour, with bright yellow armpits and a broad head with a sardonic smile.
During the normal metabolising of proteins, the constituent amino acids are broken down to form nitrogen. In their typical aquatic environment, the frogs excrete nitrogen in the form of ammonia – the simplest form of nitrogen.
Pyxis gained fame through a wonderful BBC documentary narrated by David Attenborough that showed parental care in these frogs. Pyxis stay underground until good rains have fallen and formed shallow puddles. They then come to the surface, where the males take occupancy of a puddle, with the dominant male at the centre.
Ammonia is a toxic molecule, so it must be rapidly excreted along with the loss of a large volume of water – this is no problem if you live in water and it can be replenished easily. However, when the frog aestivates because of drought, it has to conserve the water it has in its body and store the breakdown product until such time it can be excreted. Therefore, the frog changes its metabolism to make urea instead – a molecule that’s much less toxic and can be safely stored in the body. How do they do that? That was the topic of my research. Pyxicephalus adspersus – the giant bullfrog – also aestivates for long periods and probably has a similar mechanism of adaptation. We kept some in the lab in a tank as possible research subjects. They were magnificent. If there is a prince among frogs, the ‘pyxi’ must be it. They were the size of a dinner plate and weighed well over a kilogram. They
The males call for females to come hither, and the dominant, strongest male will win most fair maidens. Fertilisation takes place externally, with the male ducking the female’s head under water so that the eggs squirt out above the water – he fertilises them in mid-air! From here it’s a race against time to complete metamorphosis before the puddle dries up again. The shallow puddle is warm, so the eggs hatch rapidly. Tadpoles from all the successful matings come together into one large school, guarded by the dominant male. He will fight to protect them from any predators. If the pond starts to dry up, he will use a spade-like feature on his hind legs to dig a channel to another deeper pond. Daddy day-care. How amazing is that! Unfortunately, we don’t have the pleasure of seeing these frogs in Hermanus – they occur in the north-eastern part of the Western Cape and further inland to the north. And what happened to the lab specimens? I am happy to say that they were never the subjects of any research. They were eventually released in a wetland near Johannesburg, where I hope their progeny lives on to this day.
CIRCLE: Animals like frogs can bury themselves when ponds dry up and stay in a state of dormancy (called aestivation) for up to a year or more, until the next heavy rains. The familiar ‘platanna’ (Xenopus laevis) is an excellent example of this useful adaptation. PHOTO: Science Source BELOW: Male Bullfrogs gathering at a shallow pond. PHOTO: Whale Coast Conservation
The Giant Bullfrog (Pyxicephalus adspersus) is a prince among frogs. They grow to the size of a dinner plate and weigh well over a kilogram. They are a deep green colour, with bright yellow armpits and a broad head with a sardonic smile. PHOTO: Tyrone Ping
The endangered Western Leopard Toad’s wetland habitat habitat the coast from Cape Town to Agulhas has systematically been destroyed under the guise of “development”. PHOTO: thegreentimes.co.za
