A team of researchers from the United States, the United Kingdom and Switzerland has described six new species of direct-developing frogs from the Mexican states of Oaxaca, Mexico, Guerrero, and Jalisco.
Craugastor cueyatl sits on a Mexican 10 pesos coin (diameter is 2.8 cm). Image credit: Jeffrey W. Streicher, Natural History Museum, London.
The newly-discovered species belong to the genus Craugastor in the family Craugastoridae.
They are known as ‘direct-developing’ frogs. Rather than hatching from eggs into tadpoles like most frogs, they emerge from the eggs as perfect miniature frogs.
“With millions of these frogs living in the leaf litter, we think they’re likely to play a hugely important role in the ecosystem as a source of food for everything else, from lizards to predatory birds,” said lead author Dr. Tom Jameson, a researcher in the Department of Zoology at the University of Cambridge and the University Museum of Zoology.
“Their lifestyle is utterly fascinating. These frogs live in the dark, humid leaf litter of the forests, which is like a secret world — we don’t really know anything about what goes on there. We don’t understand their behavior, how they socialize, or how they breed.”
The new species have been named Craugastor bitonium, Craugastor candelariensis, Craugastor cueyatl, Craugastor polaclavus, Craugastor portilloensis, and Craugastor rubinus.
All six are approximately 1.5 cm long when fully grown. Adult males of the tiniest of these species, Craugastor candelariensis, grow to only 1.3 cm, making it the smallest frog species in Mexico.
“Frogs in the group known as Craugastor are very difficult to tell apart, so scientists have long suspected that more species may exist,” Dr. Jameson said.
“We’re really excited to have discovered six new Craugastor species that are completely new to science.”
Dr. Jameson and colleagues examined almost 500 Craugastor frog specimens from museums around the world.
Using DNA sequencing, they sorted the frogs into groups based on how similar their genes were.
Then CT-scanning was used to create 3D models of the frogs’ skeletons, so that physical details could be compared.
These two very different lines of evidence revealed six new species.
Known as ‘micro-endemics,’ some of them may occur only in one small area, such as a hilltop in a certain part of Mexico. This makes them incredibly vulnerable.
“These frogs potentially play a really important role in the forest ecosystem,” Dr. Jameson said.
“We need to make sure that they don’t just get wiped off the map because no-one even knows they’re there.”
The discovery is reported in a paper in the journal Herpetological Monographs.
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Tom J.M. Jameson et al. 2022. Miniaturization in Direct-Developing Frogs from Mexico with the Description of Six New Species. Herpetological Monographs 36 (1): 1-48; doi: 10.1655/0733-1347-36.1.1
