According to Michigan State University’s Chan Kin Ong, when people hear about the discovery of a new species, they often think of scenes from adventure stories.
“Most people have images of intrepid explorers braving remote mountains and other remote locations and encountering creatures that no one has ever seen before,” Chan says.
That scenario still happens from time to time. However, Chan pointed out that the reality is usually less dramatic. “But most of the time it’s not that appealing,” he added.
Scientists often identify new vertebrate species by revisiting animals already known to science. With improved tools and newer data, researchers sometimes discover that populations once thought to be the same species are actually more different than previously realized.
The mystery of the tree frog in Borneo
Chan is a herpetologist who studies amphibians and reptiles, including frogs, turtles, lizards, and snakes. Scientists have identified more than 9,000 amphibian species around the world, and about 100 to 200 new amphibian species are added each year, he said.
One example is a group of small brown frogs from Southeast Asia known as Borneo frogs. Their name comes from the tooth-like projections along their jaws. One member of this group, Limnonectes kuhlii, has been known to scientists since 1838. However, genetic research over the past two decades suggests that what appears to be a single species may actually represent as many as 18 species.
“Animals that look similar but are genetically distinct are called cryptic species,” said Professor Chan, curator of the Vertebrate Collection and core faculty member in MSU’s Ecology, Evolution, and Behavior Program.
Advances in gene sequencing have made uncovering these hidden lineages much easier. As Chan explains, “A large number of mysterious species are being discovered all over the place.”
DNA analysis reveals fewer species than expected
To determine whether these frogs had been significantly underrepresented, Chan and his colleagues collected DNA from specimens collected across a mountainous rainforest in Malaysian Borneo. The research team examined more than 13,000 genes across the frog’s genome.
Their findings were published in the journal systematic biologyshowed that frogs can be divided into several genetic groups. However, the results did not support the idea that as many as 18 species existed. Instead, evidence suggests that about six or seven of these clusters qualify as distinct species.
“It’s not just one species, but it’s not 18 species either,” Chan said.
Why species numbers matter for conservation
Determining exactly how many species exist is not just an academic debate. It has real implications for conservation.
Amphibians currently face serious threats around the world. An analysis of approximately 8,000 amphibian species in 2023 found that two out of five species are at risk of extinction, making amphibians the most endangered group of vertebrates.
Chan, who contributed to the study, emphasized that species recognition is essential for species conservation.
“There are so many undiscovered species in the world that they may go extinct before we can name them,” Chan said.
At the same time, dividing seeds too aggressively can have downsides.
“But there is also a flip side to this coin,” he added.
When scientists rapidly split a species into many smaller species, each newly defined species can appear to occupy a very narrow geographic range. This can make their protection situation appear more stringent than it actually is.
“We can’t conserve everything, so we have to triage and decide how to allocate our limited resources to what we think are the highest priorities,” Chan said. “We may be naming things that shouldn’t be a priority.”
Blurred boundaries between species
The researchers also detected significant interbreeding among the frogs.
“We found that there was a lot of gene flow going on,” Zhang said.
This exchange of genetic material between groups can blur the boundaries scientists use to define species. For this reason, Chan noted that some of the growing number of cryptic species candidates may be due to the way scientists analyze data, rather than reflecting clear biological divisions.
Borneo’s fanged frogs show that the formation of new species rarely occurs suddenly.
“It’s not like there’s going to be a boom all of a sudden. It’s more of an ongoing thing,” Chan said.
Seeds hidden in the tree of life
The fanged frog is just one example of a broader pattern that scientists are uncovering. Over the past two decades, genetic studies of many animal groups, including insects, fish, birds, and mammals, have suggested that many species may be hiding in plain sight.
Previous estimates put the total number of species on Earth at about 8.7 million. Recent models that take into account the cryptic species suggest that the actual number may be much higher, perhaps ranging from 7 to 250 times that number.
So where does the actual total fall?
“This study shows that there is a ‘gray zone’ in speciation that makes it difficult to draw the line,” said Professor Chan.
This research was supported by grants from the National Science Foundation (GRFP 1540502, 1451148, 0907996 and 1654388).
