Table Mountain Ghost Frog
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!"
I've another froggy for you, this time a Table Mountain Ghost Frog, sometimes called Rose's Ghost Frog, Heleophryne rosei. It is one of South Africa's rarest and most restricted species. It only lives in and around a few streams on Table Mountain, which rises above Cape Town. The total extent of suitable habitat is only eight square kilometres, or three square miles, encompassing all of the streams that flow year-round on the moist, eastern slopes of the mountain.
Ghost frogs constitute a family, the Heleophrynidae, consisting of seven currently recognized species in two genera. This family is only found in South Africa. The majority of the species live in the southwestern and eastern Cape, but one species, the Natal Ghost Frog, Hadromophryne natalensis, ranges as far north as the Limpopo Province, my own, which is the northernmost province of South Africa. All of the ghost frogs need fast flowing water to breed in. They have specially adapted tadpoles, with sucker-mouths as wide as their entire bodies, armed with twenty or more rows of teeth! These they use to cling onto rocks so the fast-flowing water doesn't sweep them away. The water in these streams are typically very clear and free from fish, dragonfly larvae and other predators that feed on tadpoles. It's also relatively free of bacteria and diseases. Unfortunately it is also largely free of small invertebrates or water plants the tadpoles themselves might feed on. But algae grow on places where they can find purchase, such as the surface of rocks and stones. This is what the tadpoles feed on. They work their way over the rock surfaces with their sucker-mouths eating the algae and using the teeth to pull themselves along. They can even climb by their mouths up vertical surfaces! They leave a record of their movements as 'clean' tracks over the rock surfaces, like an eraser sweeping over a dirty blackboard.
Adult ghost frogs still remain fairly close to these streams. They, too, have clinging adaptations: the tips of their fingers and toes are expanded into Y-shaped gripping pads. Although they prefer rock climbing, like tree frogs they sometimes clamber into the trees and bushes fringing the streams. Their favourite hiding places are the recesses behind waterfalls, where the splashing water and slippery surfaces make it hard going for predators to follow. Also they have flat bodies making it easy for them to slip into narrow crevices. They are very wary, hiding themselves well, and thus very difficult to see. Their presence in an area can be established by listening for their ringing calls, however, if these can be heard over the rushing of the water.
When mating time comes, ghost frogs have another adaptation. The males as well as the females develop small, hard, sharp-tipped warts called asperities on their legs, arms, backs and undersides of their jaws. They grip and caress each other with these when mating to get into the mood. Like other frogs the males clasp the females around their chests, and ejaculate their sperm over the eggs as she lays them. They lay the eggs in recesses next to flowing water, into which the tadpoles emerge. Because they spend much time in the water at this point, they develop a final adaptation, folds of skin from which they can absorb oxygen from the water; the males keep fanning themselves with their feet to improve this gas exchange.
Because these mountain streams are quite cool and food is scarce, the tadpoles grow slowly. It takes them more than a year to mature. This is why the frogs are found only where water flows year-round. In this species breeding is in Spring and Summer which is the dry season in the southwestern Cape; this ensures that any water they find would likely be permanent. The distribution of the different ghost frog species are separated by 'breaks' in the streams and catchment areas. For instance between the distribution of the Table Mountain Ghost Frog and its nearest neighbor, the Cape Ghost Frog, Heleophryne purcelli, there is a large expanse of sandy plains called the Cape Flats in which no suitable streams are found today. Similar gaps separate other species from each other. But each one of those gaps had to have been crossed at some point in the past … else, how had the ancestors of the frogs ever arrived there?
The mystery is solved when one remembers that climates did change a lot over time, especially over the past tens of thousands of years which were Ice Ages separated by interglacial periods. There was no ice in South Africa, but hotter and cooler periods also had an effect on rainfall. While the Cape Flats are dry and covered with scrubby vegetation today, there must have been a time in the past when the entire region had a moister climate and probably was covered with forest. Under such conditions frogs could make the journey over them, and colonize the Table Mountain/Cape Penninsula region. But when the climate became drier, the flats dried out, separating the frogs on Table Mountain from those on the next nearest suitable habitat in the Hottentots-Holland Mountain catchment area. With the passage of time, the frogs evolved into different species.
Similar events must have led to the evolution of all the present seven species. Because only one species occurs in any specific area, they are not usually confused with each other, but it is possible that some populations in specific areas might turn out to be distinct species. Ghost frogs generally resemble each other in size and shape, differing in the details of their coloration. All of them have vertical cat-like slit pupils, usually with a horizontal black stripe running through them to disguise the eye – but it is absent in this species. The Cape Ghost Frog has a green to brownish base colour with darker purplish or reddish blotches, and the adult frog is 45-60 mm in length, or just under to just over two inches.
Today the Table Mountain Ghost Frog is in a precarious position, trapped on the mountain and with one of South Africa's biggest and most populous cities lying around it. But the surviving wild areas are declared a nature reserve. Here the frogs can still survive in peace. They hide in crevices and caves and are so rarely seen that even though frog experts know exactly where to find them, they have been little studied. Hiding by day they come out at night to catch insects. The name 'ghost frog' might come from the fact that this species is found and might have been first seen or heard in Skeleton Gorge on Table Mountain. Ghost frogs are among the most unique of the amphibians and because the family is entirely confined to South Africa, should be considered one of the treasures of our biodiversity. It would seem ghost frogs diverged from their closest common ancestors about 160 million years ago and are at the base of the Neobatrachia or 'modern' frogs and toads.