New species of ‘pumpkin toadlet’ poisonous frog found in Brazil

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A pumpkin toadlet crawls past a bright orange mushroom, a common feature of the tiny frog’s habitat

Edelcio Muscat

Pumpkin toadlets are poisonous frogs with brilliant orange skin that are small enough to fit on a thumbnail – and researchers have uncovered a new species of these vibrant amphibians.

Ivan Nunes at São Paulo State University in Brazil and his colleagues suspected a local toadlet species (Brachycephalus ephippium) was more than it appeared. Unusually widespread for a pumpkin toadlet, the species was found throughout the southeastern coastline of Brazil. The team suspected that the wide-ranging frogs were actually multiple species with smaller ranges.

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Nunes and his team collected wild toadlets from the Project Dacnis preserve near São Paulo, measuring and comparing the physical features of 276 frogs. The team also made 76 field surveys between October 2018 and September 2019 to study the toadlets’ behaviours and habitat use.

They also included museum specimens that were collected over a range of 200 kilometres. The team analysed DNA samples from 71 toadlets, and recorded the mating calls of several males to see how they compared with those from close relatives.

Most pumpkin toadlet species are quite similar to each other. They’re exceptionally tiny frogs, among the smallest in the world at just over a centimeter long, and often have bright, tangerine skin that secretes a powerful neurotoxin.

But the researchers found that a group of toadlets in the southern Mantiqueira mountains – a rugged, forested landscape with a diverse array of frogs found nowhere else – were distinct from their neighbours. They were smaller than B. ephippium, with faded black spots and DNA that differed by about 3 per cent. These differences warranted classification as a new species: B. rotenbergae.

Like some other pumpkin toadlets, B. rotenbergae has bony plates on its skull and back that are fluorescent and glow through the skin under UV light. Nunes says it’s unknown what the fluorescent bones are for, but they might play a role in communication.

Jodi Rowley at the Australian Museum in Sydney says the discovery highlights how much we have to learn about frog biodiversity.

“Despite being amongst the most threatened groups of animals on the planet, we still have a rather terrible understanding of how many [frog] species we have,” says Rowley, who was not involved in the research.

Nunes says B. rotenbergae enjoys relative protection in its preserved habitats in high elevations, but habitat loss is a potential threat.

“We have to pay attention to the expansion of urban areas in that area,” says Nunes, adding that monitoring efforts to learn more about the toadlets’ reproduction and feeding should be undertaken.

Journal reference: PLOS ONE, DOI: 10.1371/journal.pone.0244812

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