The tadpole of a very rare toad revealed

Sterling’s Toothed Toad (Oreolalax sterlingae) is a beautiful brownish-gold toad known only from the summit of the highest mountain in Vietnam. The species was discovered in 2013, and is now known to be Critically Endangered, threatened by habitat loss and pollution. Very little is known about this toad, and until recently it wasn't known where the species bred or what its tadpoles looked like. However, on recent surveys, my colleagues and I discovered tadpoles of Sterling's Toothed Toad. The tadpoles are unique in appearance- black with bright gold markings along their tail fins. Now that we have discovered the tadpole of Sterling's Toothed Toad, we know a little more about the habitat requirements of the species and we can more effectively survey for it. Finding a little tadpole is actually a big leap forward in our knowledge of this threatened toad.

I first came accross Sterling’s Toothed Toad in 2012, while I was surveying for frogs with coleagues near the summit of Mount Fansipan. Mount Fansipan is a high (3,134 m above sea level), steep mountain, not far from the border of Vietnam and China, and is shrounded by mist most of the year. It even snows occasionally on the summit! The plants and animals of the peak are adapted for these cold, wet conditions and I expected that ou surveys would reveal unknown species. I was not disappointed.

During the surveys at night on the mountain we encountered Sterling's Toothed Toads along a rocky stream and in the surrounding vegetation and found another small frog along the edges of the same stream. I knew that they were new to science. A year later, they were both named, and shortly after that they were both declared Critically Endangered. Habitat loss and pollution, largely as a result of tourism, was really impacting the small area that they were known from. We needed to determine how best to stop these frogs from being driven to extinction, but we knew so little about them.

One of the big unknowns for Sterling's Toothed Toad was their breeding habitat and their tadpole. We suspected that they bred in the stream where they were found, but could only guess at what their tadpole looked like. On surveys at Mount Fansipan in 2015 we came accross a handful of tadpoles in the same stream. They were black with a tail lined in gold- could they belong to Sterling's Toothed Toad? The usual practise would be to collect these tadpoles, but given the precarious situation the species was in, we didn't want to do that. Instead, we took a tiny DNA sample from the tail of the tadpole. Later DNA tests confirmed that we had indeed found the tadpole of Sterling's Toothed Toad.

The discovery of the tadpole of Sterling's Toothed Toad is a big advance in our understanding of this poorly-known species that is perched on the edge of extinction. We now better understand what kind of habitat the species needs to survive and can also better survey for it- as we now know what the adults and the tadpoles look like. A tiny discovery, but an important one for the conservation of this beautiful mountain-top toad.

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

More information
Rowley, J.J.L., Tapley, B., Nguyen, T.C., Altig, R. (2017). Tadpole of the Critically Endangered Sterling’s Toothed Toad (Oreolalax sterlingae). Zootaxa. 4272:579-582.