In a new study led by The University of Kansas, scientists describe a new species of fanged frog that has been discovered in the Philippines. The Mindoro Fanged Frog was distinguished from a nearly identical species through its unique mating call.
Study lead author Mark Herr is a doctoral student at the KU Biodiversity Institute and Natural History Museum.
“This is what we call a cryptic species because it was hiding in plain sight in front of biologists, for many, many years,” said Herr.
“Scientists for the last 100 years thought that these frogs were just the same species as frogs on a different island in the Philippines because they couldn’t tell them apart physically.”
“We ran a bunch of analyses – and they do indeed look identical to the naked eye – however, they are genetically isolated. We also found differences in their mating calls. They sound quite different. So, it was a case of using acoustics to determine that the species was different, as well as the new genetic information.”
Years ago, KU scientists working on Mindoro Island had collected genetic samples from the new fanged frog, Limnonectes beloncioi, that were not analyzed until recently. The frog was assumed to belong to a species on the island of Palawan called Acanth’s Fanged Frog.
“You can look at two different things, but to the human eye without intensive investigation they might seem the same,” said Herr. “So, we took a bunch of measurements of hundreds of these frogs – how long their digits were specifically, how wide the tip of their toe was, the length of one specific segment of their leg, the diameter of their eye – in order to compare populations statistically, even if we thought they look the same.”
“We ran statistical analyses on body shape and size, including a principal component analysis which uses all the measurements at once to compare the frog morphology in multivariate space. After all that, just like the scientists before us, we found nothing to differentiate the frogs based on the shape of their bodies and their size.”
However, the fanged frogs live on islands that are separated by miles and miles of ocean, and the researchers noticed that their calls sounded different. Using a genomic analysis, the team determined the Mindoro Fanged Frog qualifies as its own distinct species.
“We ran genetic analyses of these frogs using some specific genetic markers, and we used a molecular clock model just to get a very basic estimate how long we thought that these frogs may have been separated from one another,” said Herr.
“We found they’re related to each other, they are each other’s close relatives, but we found they’d been separate for two to six million years – it’s a really long time for these frogs. And it’s very interesting that they still look so similar but sound different.”
Herr said the Mindoro frogs’ fangs are most likely used in combat for access to prime mating sites and to protect themselves from predators. The frogs are sometimes hunted by people, which made it difficult for the researchers to record their calls.
“They’re really wary of us when we’re out there with our sound recorders trying to get recordings of these frogs – that’s a really tough aspect, and we were lucky in this project that we had people over many years that were out there and had recorded both of these frogs on Palawan and Mindoro,” said Herr.
“So, we had recordings from both islands, and that’s kind of rare with this group of fanged frogs because people eat them. They call at night, but the second a flashlight or human voice wanders into the equation they’re just going to take off – because they know that they can be killed by people.”
Professor Rafe Brown said Herr’s description of the Mindoro Fanged Frog continues a long tradition of KU field research into the herpetological biodiversity of the Philippines and Southeast Asia.
“Mark’s discovery reinforces a lesson we’ve learned over and over through the years – things we thought we knew, combined with new information, emerge to teach us something completely unexpected,” said Professor Brown.
“A century ago, KU professor Edward Taylor identified the Mindoro Island population as Acanth’s Fanged Frog, the same species as he had named, a few years before, from Palawan Island – an arrangement that made very little sense.”
“Zoom forward a hundred years, and we find with new technology, genetic information and bioacoustic data that the two islands’ populations are actually very well-differentiated, as we would expect. But not morphologically; their physical characteristics have not diverged. This is a case in which the formation of species has not been accompanied by morphological differentiation – so called ‘cryptic speciation.'”
The study is published in the journal Ichthyology & Herpetology.