The spiny-throated reed frog, Hyperolius ukaguruensis, sitting on a leaf looking towards the camera

The newly described species of spiny-throated reed frog, Hyperolius ukaguruensis, may use spines on its vocal sack to communicate. Image © Christoph Liedtke

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A new species of croakless frog described from the mountains of Tanzania

Scientists have described a newfound species of frog that does not ribbit in the rainforests of Tanzania's Ukaguru Mountains. 

The race is on to learn more about the unique biodiversity within these fragile environments as human impacts threaten their survival.

The Eastern Arc Mountains stretch 1,450 kilometres from Tanzania to Kenya. They are home to a rich diversity of species, many of which are found nowhere else on Earth.

Scientists are exploring the rainforests of this mountain chain to learn more about the rarely studied amphibians and reptiles that live there.

Surveys of the Ukaguru Mountains, a section of this mountain chain in central Tanzania, have uncovered a new frog species living among the reeds of a swamp within the dense forest.

A study published in PLOS One describes the new species, Hyperolius ukaguruensis, as a type of spiny-throated reed frog named for the spines on its vocal sack. This group of frogs are found only in East Africa and have a unique characteristic: they don't make a sound.

As most frogs communicate acoustically, scientists are yet to understand more about how individuals of these species interact.

Dr Simon Loader, the Museum's Principal Curator of Vertebrates who co-authored the study, says, 'Finding this new species is really exciting, but we don't yet know how these frogs communicate with each other.'

'There's a suggestion that they do it through touch or smell using the spines on the vocal sack that might emit pheromones and which then allows the males and females to locate each other. But we can't say for sure as these frogs are still relatively unstudied.'

The spiny-throated reed frog, Hyperolius ukaguruensis, sitting on a leaf

Scientists are making exciting new discoveries about rarely studied amphibians within isolated mountain forests of Tanzania. Image © Christoph Liedtke

Why are spiny-throated reed frogs unique? 

Researchers first discovered the spiny-throated reed frogs in Malawi in the early 1970s. The first described species was Hyperolius spinigularis, named for the spines on its gularis, which is the calling pouch found on the males. 

Subsequent surveys showed that the species had a broad distribution across Tanzania and Mozambique. However, studying these frogs more closely revealed that as scientists travelled further north along the mountain chain, each population of frogs were different. Multiple species of reed frogs were eventually described.

DNA analysis confirmed that the most recently discovered Hyperolius ukaguruensis was a distinct species. They also have a slightly different colouration to other spiny-throated frogs and a unique pattern of spines on the male's vocal sac. 

'The presence of spines on the back, arms and legs are reasonably common in frogs. Having them on the vocal sacs is rarer, but certainly not unheard of,' explains Simon.

'As part of the reproduction process, males often use spines to stimulate the female when mating to produce eggs. This is why it has been suggested that the spines in this group of frogs might have something to do with reproduction.'

'It's intriguing to understand if these spines work the same way as those spines on the fingers or arms in other frogs or if it is something completely different. We honestly don't know.' 

Surveys have highlighted other exciting discoveries from this group of frogs, including observations of females guarding the eggs and squirting water over them to keep them moist.  

'This type of parental care is not typical in frogs,' says Simon.

'But many of these species within these forests are difficult to spot or are very rare. With very few observations, more research needs to be done to understand more about these unique frogs.' 

A swamp in a forest surrounded trees, bushes and other green vegetaion.

The swamp habitat within the dense rainforests of the Ukaguru Mountains where Hyperolius ukaguruensis was discovered. Image © Christoph Liedtke

A disappearing mountain forest 

Over the past 30 years, researchers have conducted amphibian and reptile surveys in the forest reserve of the Ukaguru Mountains. During this period, new species have been discovered, but some have not been recorded for many years.

Studies have shown that the climate has become warmer and drier in this area, and deforestation is happening at an alarming rate. In addition to this, an increasing number of people living in and around these forest areas threaten amphibians that rely on these moist habitats to survive.

These frogs are generally found on the top of mountains in East Africa, where the remaining patches of rainforest occur on steep mountainsides. These areas are more inaccessible and so less likely to be cultivated. 

Surveys continue to be carried out by scientists in Tanzania with colleagues from the museum to understand more about how the biodiversity of these rainforests is changing with increased pressures from human activity. 

'Some of the species that were found 30 years ago are no longer found anymore, and we suspect that's probably linked to the changes that have occurred in that place,' says Simon. 

'But then, in our last survey, we also found this new tree frog. It's an interesting story of declines, but new findings are still being made. This brings back the overall sense that there's still lots of work to do in describing biodiversity and understanding its change.'