The Manchester scientists theorize that the Costa Rican frogs' sunbathing may help kill off deadly chytrid fungal infections in their skin.
Chytrid fungi have been linked with species declines on every amphibian-inhabited continent.
The conservation collaborative Amphibian Ark estimates that half of the world's 6,000 amphibian species are now threatened with extinction and 165 species have already winked out.
In the Costa Rican frogs, the Manchester team says, unique structures and properties in their skin might be what are allowing them to sunbathe—and thus fight infection—without harm.
For example, the Costa Rican frogs are known to have highly reflective skin thanks to a pigment called pterorhodin.
This pigment allows the frogs to camouflage themselves from predators by adjusting their skin to match the infrared reflection of the leaves around them.
The team noticed that when the tree frogs bask in the sun, their skin reflectivity changes to appear almost metallic—a shift that the researchers think might be tied to regulating body temperature.
Further research with the OCT method is needed, the team says, to determine how and why the frogs make these changes.
If OCT reveals a definite link between sunbathing and fighting chytrids, it could mean that global warming is not only helping the fungi spread but is also hurting the frogs' natural defenses.
The Manchester group suspects that climate change is leading to more cloud cover in the frogs' natural habitat, which means less opportunity to bask.
Ross Alford is a biologist at Australia's James Cook University who was not involved in the OCT work.
He was among the first group of researchers to draw a link between global warming and the chytrid outbreak.
"I have suggested myself in various talks at meetings that increased cloud cover—preventing basking—could 'tip the balance' within individual infected frogs between keeping the infection under control and being overwhelmed by it," Alford said.
"So I definitely agree with that general notion."
J. Alan Pounds is an ecologist who studies tree frogs at the Monteverde Cloud Forest Preserve in Costa Rica.
He said that it's too soon to judge the effectiveness of new OCT technique in studying frog skin.
But "it's very important that we gain a better understanding of how climate change influences host-parasite ecology—and temperature regulation may be a critical part of that."
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