A closer look at spectacular red-eyed forest frogs reveals a new species

The Asian Spadefoot Frogs (Leptobrachium) are large frogs that inhabit evergreen forests throughout Asia and breed in clear, rocky streams. Although usually brown or grey to match their surroundings on the forest floor, their large eyes are often splashed with bright blue, green, red or white. During expeditions in search of frogs in the region, we often came across red-eyed Asian Spadefoot Frogs. By looking a little closer at their appearance, DNA and calls, we discovered a species that, until now, had been “hidden” from science. The Crescent Moon Spadefoot Frog (Leptobrachium lunatum) is only known from the forests of northeastern Cambodia and Central Vietnam, an area under threat from deforestation. Our discovery of this regal red-eyed frog highlights just how important these forests are.

In order to understand the true diversity of amphibians in the forests of Southeast Asia, we've been conducting collaborative expeditions in Cambodia, Laos and Vietnam, in search of frogs. For many years, we have been venturing into the forests, typically in the monsoon season, when most other biologists leave. We hike up into mountain streams and camp in hammocks or tents, searching for frogs by torchlight. In the face of deforestation, it's a race against time to discover what frogs call these forests home, so that they can be scientifically described, named, and taken into account in conservation decisions.

During our expeditions, we often encountered Asian Spadefoot Frogs (Leptobrachium). These rather large frogs are usually heard before they are seen; a deep “whooooop” or “whup whup” call echoing through the forests on wet nights. Their tadpoles, large and long-lived, can also often be seen resting on the bottom of the clear streams running through the forest. However, seeing an adult Asian Spadefoot Toad can be tricky - they are often buried in the ground or under leaves, and when they are on the surface, they are usually extremely well camouflaged except for one thing... their eyes!

Different species of Asian Spadefoot Frogs often sport a different coloured upper-iris, and that's one way you can tell species apart. However, some species share an eye colour.

Until recently, two species of “red-eyed” Asian Spadefoot Frogs were known from Cambodia and Vietnam; Leptobrachium pullum, scientifically discovered almost 100 years ago, and Leptobrachium mouhoti, scientifically discovered less than a decade ago. However, there’s been much confusion about exactly where each species was distributed, and just which of the two red-eyed frogs occurred on the Kon Tum Plateau of central Vietnam and adjacent northeastern Cambodia.

We decided to solve the mystery surrounding these regal red-eyed frogs. We took a close look at the appearance of the red-eyed frogs and their tadpoles, their advertisement calls and their DNA. We realized that the red-eyed frogs from the central Vietnam and adjacent northeastern Cambodia were actually neither known species, but were actually a third species previously unknown to science! We named the species Leptobrachium lunatum after the crescent of red in its eye, as lunatus means “shaped like a crescent moon” in latin.

Like other Asian Spadefoot Frogs, the new species lives in forests and is likely to be under threat from ongoing deforestation in the region. Now that we have formally described the species and better understand the true distribution of each of the red-eyed Asian Spadefoot Frogs from the region, we can more accurately prioritise their conservation, a vital first step to ensuring that these amazing frogs are heard calling throughout the region for generations to come.

Dr Jodi Rowley, Australian Museum Research Institute & UNSW Sydney.

Dr Bryan Stuart, North Carolina Museum of Natural Sciences, USA.

More information

• Stuart, B.L., Som, H.E., Neang, T., Hoang, H.D., Le, D.T.T., Dau, V.Q., Potter, K., & Rowley, J.J.L. (2020). Integrative Taxonomic Analysis Reveals a New Species of Leptobrachium (Anura: Megophryidae) from Northeastern Cambodia and Central Vietnam. Journal of Natural History. DOI: 10.1080/00222933.2020.1756498