Researchers have identified a new species of fanged frog, called Limnonectes cassiopeia, on the Philippine island of Luzon.
A team from the University of Kansas detailed their findings about this newly recognized species of fanged frog, Limnonectes cassiopeia, in the journal Ichthyology & Herpetology.
Interestingly, specimens of this new species have been collected about a dozen times in the past two decades, but they were all mistaken for the juvenile form of the well-known Luzon Giant Fanged Frog, which looks similar but is not closely related.
Lead researcher Mark Herr, a doctoral student at the KU Biodiversity Institute and Natural History Museum, explained, “These frogs are known for their large, fang-like bony structures in the males’ lower jaws, which are quite rare. It’s believed that these fangs might be used for fighting among males. The fangs of males are significantly larger than those of females, and the males tend to have big heads, with some of these frogs reaching sizes comparable to chickens found elsewhere in Southeast Asia.”
Herr initially recognized Limnonectes cassiopeia while conducting an extensive genetic study of Philippine fanged frogs, which includes a little over a dozen known species.
“I sequenced many of the specimens to create a solid genetic database, which helped me study their relationships,” Herr remarked. “Many species were categorized purely based on their physical characteristics in the last century and a half, prior to the advent of modern genetic analysis. Luzon had two recognized fanged frog species: Limnonectes macrocephalus, the larger one, and a medium-sized one called Limnonectes woodworthi. However, I identified a different group alongside macrocephalus that appeared as a separate branch in the genetic data.”
Discovering this previously uncharacterized species in the genetic analysis motivated Herr to closely examine museum specimens, guided by the intriguing genetic results. He wanted to determine if he could differentiate its physical traits from the Luzon Giant Fanged Frog since the genetic study suggested they had evolved separately.
Thanks to extensive research conducted in the Philippines by Herr’s faculty advisor Rafe Brown and other KU researchers, there was a wealth of specimens available at the KU Biodiversity Institute and Natural History Museum. Brown co-authored the new paper alongside KU master’s student Hannah Som.
“I double-checked my genetic findings to ensure accuracy, and everything was correct,” Herr stated. “This led me to evaluate all the Limnonectes specimens from Luzon at the museum. We have hundreds of these frogs, and I meticulously compared the 19 that were part of the new genetic group to those in the main group.”
While trying to spot differences between the two species, Herr noted how easily they could be confused for the same species.
“As a herpetologist, I spend a lot of time studying frogs. I dedicated several weeks just observing these specimens, trying to discern any noticeable distinctions, and I found none,” Herr noted. “There weren’t any significant differences in color patterns or markings.”
Herr then proceeded with precise measurements of the fanged frog specimens.
“We have numerous standardized measurements aimed at uncovering differences between populations to see if these variations indicate speciation patterns,” Herr explained. “I compared among populations, started to suspect they were distinct species, and continued with deeper evaluations of various characteristics.”
Ultimately, Herr had a significant breakthrough when he realized that the genetically unique species had smaller toe pads that were also white.
“The toe pads are significant,” Herr explained. “In proportion to their body size, these frogs have statistically smaller toe pads. I revisited all the genetically identified specimens to confirm this key characteristic — a simple physical trait that anyone could observe in the field. If someone catches one of these frogs, they can easily flip it over and see that not only are their toe pads smaller, but they are white as well. This contrasts with the main species, Limnonectes macrocephalus, which has dark gray toe pads.”
Herr highlighted how this overlooked detail is particularly surprising given the high population density on Luzon, which is even greater than that of Great Britain.
“People on Luzon have been catching these frogs for over a century,” he said, noting that they form a part of the diet for several indigenous groups. “These frogs have white toe pads but I thought, who would notice that? Who would consider it? With the genetic insights we now possess, I realized there was something different about these frogs. I knew I had to investigate further. The frogs are genetically distinct; hence, I thought it would be worthwhile to see if that single trait indicated a broader difference in their overall body structure and appearance.”
Indeed, Herr was inspired by the constellation Cassiopeia, as the new species has five white toe pads, leading him to name it Limnonectes cassiopeia.
As time progressed, another significant difference came to Herr’s attention — the new species, Limnonectes cassiopeia, develops its notable large head earlier in its growth stage compared to Limnonectes macrocephalus.
“It’s obvious that both types of macrocephalus frogs might overlap in size since they all start tiny, and you wouldn’t be able to tell them apart,” he noted. “For the past 25 years, everyone who caught one would have assumed they were just juvenile macrocephalus. However, I did measurements to conclude that once the males approach sexual maturity, they develop wider heads and prominent fangs. In many instances, male Limnonectes are found with head scars, likely from battling one another. My analysis indicated that the larger heads start appearing in the new genetic group at an overall smaller body size.”
With the new species now acknowledged, Herr looks forward to discovering more about its behavior in its natural habitat and how it differentiates itself from Limnonectes macrocephalus.
“Now that we know they’re distinct, we can observe them and research their natural history in detail. They may behave very differently in the wild,” he remarked. “That’s truly exciting for me.”
