Six new species of tiny frogs discovered in Mexico

Scientists have discovered six new species of thumbnail-sized frogs in the forests of Mexico, one of which has earned the distinction of Mexico’s smallest frog.

All six species are smaller than a British 1 pence coin – around 15mm long – when mature. The adult males of the smallest of these species, named Craugastor candelariensisreach only 13 mm.

The newly discovered species are known as “direct development” frogs: rather than hatching from eggs into tadpoles like most frogs, they emerge from eggs as perfect miniature frogs. And they are so small that they are at the very bottom of the forest food chain.

“With millions of these frogs living in leaf litter, we believe they are likely to play an extremely important role in the ecosystem as a food source for everything from lizards to predatory birds,” said said Jameson.

The discovery, by researchers from the University of Cambridge, the Natural History Museum in London and the University of Texas at Arlington, is published in the journal Herpetological monographs.

“So far these new species have gone unnoticed because they are small and brown and look a lot like other frogs,” said Tom Jameson, a researcher in the Department of Zoology and Museum of Zoology at the University of Cambridge, who has led the study.

“Their lifestyle is quite fascinating,” he added. “These frogs live in the dark, damp forest litter, which is like a secret world – we really don’t know what’s going on there. We don’t understand their behavior, how they socialize or how they reproduce.”

The study involved bringing together nearly 500 frog specimens from museums around the world, which had been collected in Mexico, and using new methods to categorize the relationships between them.

Using DNA sequencing, the team sorted the frogs into groups based on the similarity of their genes. Next, CT scans were used to create 3D models of the frogs’ skeletons, so physical details could be compared. These two very different lines of evidence revealed six new species of frogs.

“The frogs of the group known as Craugastor are very difficult to tell apart, so scientists have long suspected that other species may exist. We are delighted to have discovered six new Craugastor completely new species to science,” Jameson said.

The new species were named Craugastor bitonium, Craugastor candelariensis, Craugastor cueyatl, Craugastor polaclavus, Craugastor portilloensis, and Craugastor rubinus. Jameson is particularly pleased with the name cueyatl — it means “frog” in the native language, Nahuatl, spoken in the Valley of Mexico where this species was found.

“We chose the name cueyatl honor the rich human history of the Valley of Mexico and the local people who have probably known about these frogs far longer than we have,” he said.

Known as “micro-endemics,” some of the newly discovered frogs may only be found in a small area, such as a hilltop in a certain part of Mexico. This makes them incredibly vulnerable.

“We named Craugastor rubinus after the hillside garnet mines where they are,” Jameson said. “Unfortunately, it only takes one mine to expand and those frogs could go extinct.

Habitat loss can also result from climate change. And the frogs are threatened by a deadly fungal disease, chytridiomycosis, which is wiping out amphibian populations around the world.

But the researchers hope there is a future for their little frogs. They have identified key protected areas across Mexico where the six new species live – and now hope to work with the government and NGOs in Mexico to link these areas together.

“These frogs potentially play a very important role in the forest ecosystem,” Jameson said. “We have to make sure they’re not just wiped off the map because no one even knows they’re there.”

He thinks there are probably many more species of Craugastor frog yet to be discovered, simply because no one has yet had the opportunity to look for them.

“We looked at maps of where the original expeditions went to find frogs in Mexico, and found whole valleys and river systems where no one went,” he said. “Because the tiny frogs live in tiny areas, we can be pretty sure there are a whole bunch of other undiscovered species out there – all we have to do is go find them.”

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