Do chytrid fungi pose a threat to northern Vietnam’s frogs?

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ZSL London Zoo’s Curator of Amphibians and Reptiles Ben Tapley discusses climbing mountains and battling the elements as part of a collaborative mission to discover more about the range of the devastating amphibian disease, chytrid - revealing the results, published today in Herpetological Review*.

Read the paper here

Amphibians are in serious trouble and amphibian populations around the world are declining fast. A variety of emerging infectious diseases are known to be driving this global decline: Chytridiomycosis is one such disease and it is caused by the amphibian chytrid fungi Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal). Between them, these pathogens have been implicated in the declines of more than 500 amphibian species globally.

We now know that both Bd and Bsal originated in Asia and there is a growing interest in the ecology and distribution of chytrids within their native range. 

In 2015, ZSL began collaborating with Hoang Lien National Park, the Australian Museum and the Asian Turtle Program of Indo Myanmar Conservation. Together, we work in the Hoang Lien Range in northern Vietnam which is home to more than 80 species of amphibian, many of which are highly threatened, including several Evolutionarily Distinct and Globally Endangered (EDGE) amphibians such as Botsford’s Leaf-Litter Frog (Leptobrachella botsfordi) and the Bicolored Moss Frog (Theloderma bicolor). 

frog

We investigated the presence of Bd in the Hoang Lien Range across an elevational gradient, and looked for patterns in Bd infection in space, time and amphibian species. We also investigated the presence of Bsal in the Hoang Lien Range. 

Over a period of five years we collected over 600 samples from 40 different species of frog found in the Hoang Lien Range. This represents one of the most intensive surveys on chytrid fungi undertaken in mainland southeast Asia to date. 

The sampling involved passing a swab gently over the skin of the abdomen, thighs, calves and feet of the frog, but catching the frogs was not always easy - many of them live in fast flowing streams or are found high up in the canopy and quite a few frogs hopped away before we could sample them.

Scientists swab frogs

We climbed the three highest peaks in northern Vietnam (repeatedly) to get these data, battling pouring rain, floods, and waded thigh deep in muddy buffalo wallows and across torrential streams to sample a diverse array of frogs. You really have to have a passion for amphibians to undertake this kind of work.

It was good news for the area: we did not detect Bsal and only found six individual amphibians with Bd infections. Two of the frogs with Bd infections were individuals from the two Asian horned frogs described by our team in 2018, which are potentially highly threatened. 

We did not detect Bd in any of the Critically Endangered or EDGE species and we did not encounter any amphibians exhibiting clinical signs of disease. One of the species positive for Bd is known to be internationally traded for the exotic pet trade; the international amphibian trade has been widely implicated in the spread of amphibian pathogens, and our findings further demonstrate the potential risk that the wildlife trade may pose to in terms of spreading wildlife disease.

mossy frog 

Our findings were similar to those from other studies in mainland southeast Asia, where there is a low-prevalence and low-intensity of Bd infection. 

Whilst our results indicate that chytrids are not a current major threat to this globally significant amphibian species assemblage, we urge ongoing monitoring against the backdrop of climate change, which is known to increase the susceptibility of some amphibians to chytrids. 

Acknowledgements

We are extremely grateful to the staff at Hoang Lien National Park and Bat Xat Nature Reserve for their assistance and collaboration. This work was supported by the Ocean Park Conservation Foundation Hong Kong and by The EDGE of Existence Programme.

About the paper’s authors:

  • Benjamin Tapley, Curator of Reptiles and Amphibians, Zoological Society of London
  • Luan Thanh Nguyen, Botsford’s leaf-litter frog EDGE Fellow, Asian Turtle Program / Indo Myanmar Conservation
  • Jodi Rowley, Curator of Amphibian & Reptile Conservation Biology at the Australian Museum and UNSW
  • Phil Jervis, PhD candidate, Zoological Society of London, Institute of Zoology
  • Lola Brookes, Zoological Society of London, Royal Veterinary College and Imperial College London, funded by the NC3Rs
  • Daniel Kane, Senior Keeper, Reptiles and amphibians Zoological Society of London

*
Tapley, B., Jervis, P., Nguyen, L.T., Portway, C., Nguyen, C.T., Luong, H.V., Kane, D., Brookes, L., Perkins, M.W., Ghosh, P., Wierzbicki, C., Shelton, J., Fisher, M.C., Rowley, J.J.L. 2020. Low prevalence of Batrachochytrium dendrobatidis detected in amphibians from Vietnam’s highest mountains. Herpetological review. 51 (4): 726-732

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