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New toad from Kenyan volcano reveals hidden evolution of African amphibians
The hunt is on for the Kenyan volcano toad – a newly described species which has only ever been found once.
The sole specimen is surprising scientists with its unusual appearance and evolutionary relationships to other toads, which point to an intriguing evolutionary history in East Africa.
A lone toad discovered high in the forests of Mount Kenya has been described as its very own genus and species, but no one’s quite sure how it got there.
Named the Kenyan volcano toad, Kenyaphrynoides vulcani’s origins are shrouded in mystery. Kenya is known to have had a turbulent geological past which is thought to have been too unstable for rainforests to last for a long time, limiting the opportunity for any forest specialists to evolve.
However, the discovery of the Kenyan volcano toad calls this into question. Thought to have split from its closest relatives around 20 million years ago, it suggests that some regions of Kenya must have been stable enough for some species to survive.
With just one male found so far, scientists are now looking for more individuals so that they can piece together its extraordinary evolution and learn more about its natural history.
Dr Simon Loader, the Natural History Museum’s Principal Curator in Charge of Vertebrates, was a co-author on the paper.
‘Kenya’s mountains are mostly volcanic and comparatively new, so to find an ancient lineage that has persisted for millions of years is mindblowing,’ Simon says. ‘It’s a real conundrum to figure out how it got here.’
‘While we’re not certain, it seems like it might once have had a wider distribution. As the climate changed over tens of millions of years, it tracked the tropical forest as it moved, with the toad’s final destination being the top of Mount Kenya.’
The findings of the study were published in the Zoological Journal of the Linnean Society.
The discovery of Kenyaphrynoides vulcani
When it comes to east African amphibians, Tanzania is particularly rich in diversity of frogs and toads. This is explained by the long-term persistence of forest in this region. It is part of a biodiversity hotspot, having the perfect setting for an array of different and unique amphibian groups to have evolved.
In contrast, Kenya’s geological history has been much less stable, with tectonic activity likely to have reduced the stability of forest ecosystems in the region. This, in turn, impacts the diversity of amphibians which can live there.
Mount Kenya is an extinct volcano that only formed around three million years ago, making it geologically very young ©Kristof Kovacs/Shutterstock
This difference in amphibian species between Kenya and its neighbouring countries is so pronounced that it gives its name to a term describing the effect: the Kenyan Interval.
As a result many of Kenya’s amphibians descend from groups that originated in nearby countries, with relatively few unique groups of its own. But K. vulcani suggests that the Kenyan Interval may not be all that it appears.
When the toad was first discovered in a pitfall on Mount Kenya back in 2015, it already appeared to be very different from the species normally found in the region.
Dr Patrick Malonza and Dr Victor Wasonga, curators at the National Museums of Kenya and co-authors on the paper, were the first to realise that this toad was something new.
‘We were really surprised to see this animal, as it didn’t look like anything we had seen before,’ the co-authors said. ‘The closest resemblance was to a forest tree toad called Churamiti maridadi, which lives hundreds of kilometres away in the Ukaguru mountains of Tanzania.’
It was a distinctive species, with a thinner, more frog-like body and distinctive green and brown markings. To try and identify it, the Kenyan team turned to Simon and his colleagues for help, loaning the specimen to the Natural History Museum in London.
To confirm what the toad was, it needed to be compared to other species that live in the region. The Natural History Museum has a world-leading collection of toads from east Africa, which have been built up by successive curators over a number of years.
Simon compared characteristics such as its shape, colour and DNA to the other specimens in the collection, revealing that not only was the toad a new species, but in fact an even more distinct branch of the tree of life known as a genus.
What do we know about this toad?
While the Kenyan volcano toad has now been formally named and described, there’s still a lot that’s to be found out about it – not least its lifestyle.
The specimen holds clues that might help to reveal this. For one, it has large hands with expanded fingertips, suggesting that it probably climbs and lives in the trees. The new species also has distinctive sharp spike like structures known as nuptial spines that could hint at its breeding behaviour.
The researchers suspect the toad has gone unnoticed as it lives in the canopy of the lush forest that surrounds the mountain ©Taher Ammar/Shutterstock
‘Nuptial spines are found in many male frogs and toads, as they help the male grab on to a female and stimulate them into breeding,’ Simon explains. ‘We’re not really sure how it breeds at the moment, but given its relationship to other forest East African toads, it’s probably something unusual.’
Currently, these ideas are just hypotheses. The team hopes to find more individuals to help them confirm or deny their suspicions, with a female being particularly sought after to reveal more about its reproduction.
Doing so, however, has proven challenging. Since being discovered in 2015, the volcano toad has not been seen again.
Dr Christoph Liedtke, a postdoctoral researcher at the Estación Biológica de Doñana, Spain, is the first author on the paper.
‘It’s possible that its population might be in decline, as many of its close relatives are highly endangered and live in small areas where habitat quality is declining,’ says Christoph. ‘It’s difficult to tell, however, as Mount Kenya is a large area that has not been fully and regularly surveyed.’
While the hunt continues, the sole specimen of the Kenyan volcano toad will be returned to the National Museums of Kenya so that researchers can continue to study the toad. The discovery of this unusual species in such an unexpected place suggests that there could be even more toads hiding in the country’s rich montane forests.
‘We don’t know everything about the main groups of amphibians, and probably only understand a small proportion of their true diversity,’ Dr Liedtke says. ‘While this new genus doesn’t change our whole view of the Kenyan Interval, it suggests that the reality is much more complex than has been suggested.’
‘We can’t presume on geology alone that other amphibian lineages don’t exist, suggesting there could be more forest toads to find in east Africa.’
