The six species of frogs that have been found in the forests of Mexico are smaller than a British penny coin , measuring about 15 mm in length, when fully grown. Adult males of the smallest of the species, called Craugastor candelariensis , measure just 13 mm.
These frogs are very special, and not just because of their diminutive size. The species discovered have the peculiarity of hatching from eggs fully formed , not as tadpoles, but as miniature frogs. Due to this characteristic, these frogs are known as “direct development” frogs.
“With millions of these frogs living in the leaf litter, we think they likely play an enormously important role in the ecosystem as a food source for everything from lizards to predatory birds,” said Tom Jameson, a researcher at the Department of Zoology and the University Museum of Zoology at the University of Cambridge, who led the study that has been published in the journal Herpetological Monographs .
“Until now these new species have gone unnoticed because they are small and brown and look a lot like other frogs,” said Tom Jameson. “His lifestyle is absolutely fascinating,” he added. “These frogs live in the dark, wet leaf litter of the forests, which is like a secret world: we don’t really know anything that goes on there. We don’t understand their behavior, how they socialize or how they reproduce.”
The study consisted of gathering almost 500 frog specimens from museums around the world, which had been collected in Mexico, and using new methods to classify the relationships between them.
Using DNA sequencing, the team classified the frogs into groups based on the similarity of their genes. Computed tomography was then used to create 3D models of the animals’ skeletons so that physical details could be compared. These two very different lines of evidence revealed six new species of frogs.
“Frogs in the group known as Craugastor are very difficult to distinguish, which is why scientists have long suspected that more species may exist. We are very pleased to have discovered six new species of Craugastor that are completely new to science,” he said. Jameson.
The new species have been named Craugastor bitonium , Craugastor candelariensis , Craugastor cueyatl , Craugastor polaclavus , Craugastor portilloensis , and Craugastor rubinus . Jameson is especially pleased with the name cueyatl: it means “frog” in the indigenous language, Nahuatl, spoken in the Valley of Mexico where this species was found.” We chose the name cueyatl in honor of the valley’s rich human history of Mexico and the local population, who have probably known these frogs for much longer than we have,” he says.
Known as “microendemics,” some of the newly discovered frogs may appear only in a small area, like 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 found,” explains Jameson. “Unfortunately, the extension of a mine will be enough for these frogs to disappear.”
Habitat loss may also be a consequence of climate change. In addition, frogs are threatened by a deadly fungal disease , chytridiomycosis, which is wiping out amphibian populations around the world.
The researchers are hopeful that their little frogs have a future. They have identified key protected areas throughout Mexico where the six new species live, and now hope to work with the Mexican government and NGOs to connect these areas. “These frogs can play a very important role in the forest ecosystem,” says Jameson. “We have to make sure they don’t disappear off the map because no one knows they’re there.”
Jameson believes that there are probably many more Craugastor frog species yet to be discovered , simply because no one has been looking for them. “We’ve looked at maps of where the original frog expeditions went in Mexico, and we’ve found entire valleys and river systems that no one went to,” he said. “As tiny frogs live in tiny areas, we can be pretty sure there are plenty of other undiscovered species out there – all we have to do is go looking for them.”
Researchers from the University of Cambridge, the Natural History Museum in London and the University of Texas at Arlington have participated in the study.
Referencia: Jameson, T. et al. 2022. Miniaturization in Direct-Developing Frogs from Mexico with the Description of Six New Species. Herpetological Monographs. DOI: https://doi.org/10.1655/0733-1347-36.1.1
