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Episode 335: The Giant Goliath Frog

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The hefty Goliath Frog, with human hands for scale! (Image from The New Scientist)

You might not think of frogs as being Goliaths, but as frogs go, the Goliath Frog is pretty huge! The largest known frog was recorded reaching sizes up to 3.3kg!

The Goliath Frog is part of the Conraua genus, a diverse group that spreads across Sub Saharan Africa. Arising sometime on the Oligocene to mid-Miocene, the ancestors of the modern frogs diverged into a few major lineages that seem to follow the fragmentation that the large tropical forests went through at this time.

Found throughout equatorial Guinea and Cameroon, the goliath frog prefers some very particular habitat; waterfalls or fast flowing rivers with rocky outcrops, rapids and waterfalls in low land and mid altitude rainforests, no higher than 1000 metres above sea level (ASL).

Why so large? The specific biology of the Goliath Frog

For a long time, scientists could not provide a good hypothesis as to why the Goliath frog could reach such large sizes when the vast majority of frog species were not much larger than a few inches. With very little known about them in the wild, scientists have gone into the field to try and observe these amphibians, and what they found may explain why they can attain such a massive size.

Male frogs were observed constructing nests for spawning, using one of three major nest types. They will either utilize rock pools cleared of leaf litter, existing washouts on riverbanks or they will dig depressions in riverbanks with their legs. Does this DIY home improvement explain their size? The moving of large items of stones or branches needs some serious strength for a frog, and so over time this breeding strategy evolved the Goliath frog into the hefty amphibian it is today!

A Goliath Frog nest being observed by researchers (image from Mongabay)

These nests are used for egg deposition multiple times and keep the eggs from being washed away in fast flowing currents and protect them from predators. Males will guard these egg nests until the tadpoles hatch and disperse away. Tadpoles begin to develop in the first month after hatching and by the second month their activity begins to increase, and they feed on leaves and other plant detritus. Their mouth and eyes develop function, and their teeth start to develop. By the third month, posterior legs have started to form, and the tail begins to regress. By the fourth month, the tail is completely resorbed, and the tadpoles are almost completely metamorphosed into the adult frog.

The tadpoles of the Goliath Frog (Image from San Diego Zoo)

The goliath frog has excessive skin folds that allows them to conduct higher levels of respiratory gas exchange at the higher altitudes they are sometimes found at. Unlike other frogs, the goliath frog unusually doesn’t have vocal sacs, so they don’t rely on calls in the way other frogs do, for territory defence or mating. Also, in contrast to other frogs, the goliath frog has a proportionally much smaller heart and lungs. It is likely that these have evolved to be smaller due to their hunting behaviour. Goliath frogs are omnivores, although they prefer a carnivorous diet, and will eat anything from arachnids, gastropods, insects and crustaceans to vegetation. They are sit and wait predators, preferring to hide on the riverbank and waiting for a tasty morsel to drift across their line of sight. This means they are not active predators, so they can get away with having a significantly reduced metabolic rate, as their energy requirements are much lower than a frog that chases after its prey.

A giant frog facing giant threats

Now classified as endangered by the IUCN red list, there are estimates that Goliath frogs have declined by as much as 50% in the last decade, based off the limited surveys that have been done. The true toll could be even worse; amphibians are difficult to survey in comparison to a lot of other animals.

The major factor behind these declines is loss of habitat from conversion of rainforest to farmland, construction of roads, hydroelectric dams that can affect the water falls and fast flowing rivers they live in, and exploitation of forests for timber, palm oil and cocoa bean plantations. Fragmentation of habitat is particularly serious for amphibians, who cannot move from one patch of undisturbed land to another, as they can’t travel large distances or survive without water for long periods. In addition to these pressures, frog meat is high on the bushmeat menu, and is an important protein source for many indigenous communities. Small scale hunting for subsistence alone wouldn’t be so serious, but coupled with habitat loss and larger scale, commercial bushmeat hunting with modern day weapons and traps, is pushing this frog dangerously close to extinction.

Goliath frogs being collected for a bushmeat market in Cameroon (image from erudef.org)

The dumping of industrial chemicals into rivers is also a unique challenge for amphibians, including the goliath frog. High concentrations of chemicals will affect tadpole development and could even lead to mass die offs of tadpoles.

When geneticists tested the mitochondrial genes of several Goliath frog populations, they found very low genetic diversity between individuals and populations. This is particularly concerning for a species that is declining, as they could easily slide into inbreeding depression, affecting their health and reproductive efficiency. The scientists suggested that poaching could be behind this low genetic diversity, and that the Cameroonian government should implement some conservation translocations to improve genetic diversity and gene flow between populations.

There is a great scourge that is affecting amphibians across the globe, a deadly fungal disease called chytridiomycosis. This insidious micro-organism was first noticed in the 1980s, when mass mortality of amphibians was recorded, particularly in tropical forests. It invades the layers of the skin, attacking and damaging the outer keratin layer. As a skin infection, this may not seem so serious, but the skin of a frog is physiologically active, regulating respiration, water and electrolyte transfer. Although the exact mechanism of death is uncertain, it is likely related to electrolyte depletion, osmotic imbalance and reducing the amphibian’s ability to breathe. Infections will worsen as the frogs grow, as tadpoles have very little keratinized skin but this increases as the frog develops, until eventually the whole skin is seething with the fungus. Chytrid is easily transmitted through close contact but can even live in and infect frogs through the water, easily infesting entire populations and ecosystems. So far, there is no effective treatment for chytrid, or any effective way to stop it spreading.

An Andean frog with a devastating chytrid infection. The fungus has completely invaded the keratin of the skin (image from the New Scientist)

Conservation optimism

Although it is facing a difficult future, the goliath frog is not being ignored. Under Cameroonian law they are protected under Class A laws, meaning most hunting is prohibited, although this law is unfortunately hard to enforce in the vast forests where staffing levels are limited. The Cameroonian government have also placed restrictions on the number of Goliath frogs that can be exported for the pet trade, limiting the numbers to 300 frogs per year. In recent years, government bodies have tried to enforce laws more efficiently, and news has travelled to even the most remote areas that there are newer, stricter laws in place to protect the frog.

Protecting the frog is a complex issue, however. Many indigenous people heavily rely on bushmeat, including the Goliath frog, both for sustenance and income, and restrictions on hunting could devastate their livelihoods. A lot of work is being done in trying to find the locals new streams of income, including the breeding of snails for food. There will be significant challenges in changing attitudes and cultures around eating the Goliath frogs.

A Goliath Frog chilling in the fast flowing rivers of its native habitat (image from San Diego Zoo)

There has also been some good news from recent surveys conducted by scientists and conservationists. A study published in 2022 found that Goliath frogs are actually more tolerant to habitat disruption than once thought. Comparing undisturbed areas in national parks and more disturbed areas, the researchers found that Goliath frog populations were surviving quite comfortably in areas where the river dynamics were altered. This survey also highlighted some habitat features that it is important to preserve, like the riparian vegetation that the frogs use to ambush their prey from, and that more population monitoring is urgently needed. Currently there is no national monitoring programme in place. Fortunately, we do know that Goliath frogs are found in relative abundance in several protected National Parks, like the Campo-Ma’an National Park and the Ebo National Park in Cameroon, which have very limited human disturbance.

Unfortunately, there has been limited success in tackling that great plague of the amphibian world, the Chytrid infection. There has been some research into the disease, but very little action on any of the potential treatments or prophylactics. There are some suggestions that antifungal drugs can be pumped into water sources, or possibly a vaccine that can be taken up from the water through the skin. There are even some early signs that certain species may be evolving some natural genetic resistance, similar to the resistance to another fungal disease, white nose syndrome, which is a serious and often fatal infection in bats. Perhaps nature will provide its own solution? Time will tell.

As a unique and rather cute amphibian, Goliath frogs have been imported in huge numbers in the past to fuel the zoo and pet trade, but they are shy and hard to manage in captivity. Currently, there are no plans to set up a breeding programme, but rather more a of a focus on community outreach and protecting their habitat.

The conservation leadership programme is a partnership between some of the worlds biggest conservation organisations, and is designed to support early career conservationists in their chosen projects. There is a dedicated programme for the Goliath Frog run by the Cameroonian scientist Cedric Fogwan. His project aims to interview locals to determine their views on conservation projects and increase their participation in conservation projects. Snail farming will also be initiated to bring income into the community in a more sustainable way. You can learn all about Cedric’s fantastic project at Saving the Endangered goliath frog in Cameroon – Conservation Leadership Programme, and more about the conservation leadership project at Home – Conservation Leadership Programme

Cedric Fogwan, one of the scientists working with the conservation leadership programme, holding a Goliath Frog (image from BBC news)

Although the Goliath Frog does live in some protected areas, there is still a serious threat to vast regions of their range from anthropogenic change and climate change causing vast areas of desertification. To tackle this, the Great Green Wall is rewilding project that is aiming to regreen the drylands of Africa. The drylands are seriously impacting not just plants and animals, but also millions of people who relied on the once thriving ecosystems for income, food and shelter. The project aims to plant an 800km wall of trees that will reverse the vast damage that has been done to these habitats. Set up in 1987, the project has grown 27 million trees and restored and protected 167 thousand acres of land. They have made some fantastic progress, but there is still a long way to go. To learn more and even help out, check out Great Green Wall — The Great Green Wall Initiative

The aims of the Great Green Wall initiative (image from education.nationalgeographic.org)

As unsustainable palm oil agriculture is affecting not just the Goliath Frog but also many other species we cover on the podcast, you can play an active role in reducing the use of unsustainable palm oil and forcing large industries to change their supply streams to be less damaging to ecosystems. You can download the Palm Oil Scan App, which shows which companies and products are failing to meet sustainability standards by scanning the barcode on any product you buy. Learn all about it and download it here WAZA Launches PalmOil Scan- An App Empowering Consumers to Make Sustainable Decisions – WAZA

The palm oil scan app that can help you shop more sustainably

You don’t have to be a field scientist to be a conservationist and make positive changes for the world!

Awesome videos!


Blackburn, D.C. Nielsen, S.V. Barej, M.F. Doumbia, J. Hirschfeld, M. Kouame, N.N. Lawson, D. Loader, S. Ofori-Boateng, C. Stanley, E.L. and Rodel, M.O. ‘Evolution of the African slippery frogs including the world’s largest living frog.’ Zoologica Scripta

Gonwouo, N.L. Schafer, M. Tsekane, S.J. Hirschfeld, M. Tchassem, F.A. and Rodel, M.O. (2022) ‘Goliath Frog abundance in relation to frog age, habitat and human activity.’ Amphibian and Reptile Conservation

Nguiffo, D.N. Mpoame, M. and Wondji, C.S. (2019) ‘Genetic diversity and population structure of goliath frogs from Cameroon.’ Mitochondrial DNA

Schafer, M. Tsekane, S.J. Tchassem, A.M. Drakulic, S. Kameni, M. Gonwouo, N.L. and Rodel, M.O. (2019) ‘Goliath frogs build nests for spawning- the reason for their gigantism? Journal of Natural History

Webb, R.J. and Waddle, A.W. (2022) ‘Frogs vs fungus: the emergence of amphibian chytridiomycosis.’ Microbiology


May 24, 2023
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