Where did all the tiny brown frogs come from?

Southeast Asia and southern China are well-known centers of biodiversity, but also regions where biodiversity is still being rapidly discovered, and is increasingly threatened. We don’t yet know the true species diversity of the region, or the processes that created the incredible diversity of plants and animals in the region, but a knowledge of both these are vital to make informed conservation decisions. This is where some tiny frogs come in. By examining the DNA of a group of frog species across the entire region, we have gained a better picture of biodiversity evolution in Southeast Asia and southern China, and revealed just how many species of small brown frogs there may really be.

Southeast Asia and southern China have intricate geological and climatological histories. It’s this complexity that makes the region a perfect place to understand when, where and why species diversified. It’s also a race against time (and deforestation) to discover the true species diversity of the region, so that we can know where we should be prioritising conservation actions- such as where to focus on habitat protection.

Asian Leaf-litter frogs (genus Leptolalax) are a group of around 50 forest-dependent species distributed across Southeast Asia and southern China. They are small (generally less than 5cm in body length), dependent on evergreen forest and aren’t able to move very far. These characteristics make them ideal for looking at patterns of diversity and drivers of speciation. Species in the genus are also still being discovered at a rapid rate (more than 60% have been discovered since 2000), and many are threatened with extinction, including the Critically Endangered Botsford’s Leaf-litter Frog (Leptolalax botsfordi).

Many Asian Leaf-litter frogs look incredibly similar, so to better understand their true species diversity and evolutionary history, we generated molecular data for most known species in the group, from across their geographic range. This was only made possible due to the collaboration of a large team of biologists from across the world.

We discovered that there are likely at least 15 unrecognized species of Leaf-litter Frog - species yet to be formally named and therefore taken into consideration in conservation management in the region. We also reveal evolutionary relationships, including which species are most closely related to each other, and discover that some Asian Leaf-litter frogs are more related to Borneo Frogs (genus Leptobrachella), than to other Leaf-litter Frogs- meaning that further work is urgently needed to sort out the taxonomy of the group.

Our research revealed that Borneo and Vietnam have played incredibly important roles as centres of diversification in Asian Leaf-litter Frogs. The group appears to have originated in Borneo and then colonized mainland Asia, and both climatic changes and tectonic movements have driven species diversification. Vietnam, with its complex terrain, is a particular centre of diversity for Asian Leaf-litter Frogs.

Tiny brown frogs from across Southeast Asia and southern China, through their DNA, have provided us a better understanding of where and how the unique biodiversity of the region evolved. They have also given us a glimpse of just how much biodiversity remains to be discovered in the region. We hope this information will allow us to make better conservation decisions, ensuring that these tiny brown frogs, along with much of the forest that they call home, will still be around for future generations.

Dr Jodi Rowley
Curator, Amphibian & Reptile Conservation Biology
AMRI & UNSW

More information:

• Chen, J.M., Poyarkov Jr. N.A., Suwannapoom, C., Lathrop, A., Wu, Y-H., Zhou, W-W., Yuan, Z.Y., Jin, J-Q., Liu, H-Q., Nguyen, T.Q., Nguyen, S.N., Duong, T.V., Eto, K., Nishikawa, K., Matsui, M., Orlov, N.L., Stuart, B., Brown, R. Rowley, J.J.L., Murphy, R.W., Wang, Y-Y., Che, J. (2018). Large-scale phylogenetic analyses provide insights into unrecognized diversity and historical biogeography of Asian leaf-litter frogs, genus Leptolalax (Anura: Megophryidae). Molecular Phylogenetics and Evolution. 124:162-171.