Sunbathing frog's future under a cloud

Animal conservationists are turning to physics to investigate whether global warming is responsible for killing sun-loving South American tree frogs.

The Manchester team with a tree frog

In a collaborative project, researchers in The Photon Science Institute (PSI) at The University of Manchester have joined forces with The Manchester Museum to investigate the properties of the tree frogs’ skin using a technique called Optical Coherence Tomography (OCT).

This non-invasive technique, which does not cause harm or distress to the frogs, allows images to be obtained from within tissue and the Manchester team believe this innovative application of OCT could hold the key to understanding the alarming global decline in amphibians.

Andrew Gray, curator of Herpetology at the museum, said: “With a third of the world’s amphibians currently under threat it’s vitally important we do our utmost to investigate the reasons why they are dying out at such an alarming rate. The imaging technique we use is completely non-invasive and does not harm the frogs in any way. As an animal conservationist, I simply would not allow any research that distressed these amazing creatures.”

When in their natural habitat, the Costa Rican tree frogs being studied in Manchester prefer to live on leaves and branches high above the ground. They enjoy basking in the hot sun - unusual because frogs normally avoid prolonged exposure to high levels of light due to the risk of overheating and dehydration. The Manchester team’s hypothesis is that global warming is leading to more cloud cover in the frogs’ natural habitat. They believe this is denying them the opportunity to ‘sunbathe’ and kill off fatal Chytrid fungal infections, leading to many species dying out.

In their work so far, the team have observed that the skin of basking tree frogs sometimes undergoes a visible change and becomes almost metallic in texture. They think that when this happens, the level of absorption and reflection and the skin temperature also changes.

As part of their studies, they want to use OCT to compare structural changes in the skin of tree frogs with the structural changes in the skin of frogs that do not have the same high levels of infrared reflectance.

Dr Mark Dickinson, a physicist at the University, said: “This is a great example of an exciting interdisciplinary research project that draws on expertise right across the university. It is proof that interdisciplinary research is not just a fashionable expression we band around, but something we actually do.”