Glass frogs are famous for their translucent skin, but, until now, the reason for this strange feature received no experimental attention.
A team of scientists from Bristol University, McMaster University, and Universidad de Las Américas Quito, trying to establish the ecological importance of glass frog translucent and, in doing so, has revealed a new form of camouflage.
Using a combination of behavioral tests in the field, computational visual modeling and computer-based detection experiments, the study was published in PNAS revealed that, although translucent glass frogs act as camouflage, the mechanism is different from true transparency.
The lead author, Dr. James Barnett who started his research while earning a Ph.D. student at Bristol University and now based at McMaster University in Canada, said:
“Frogs are always green but look bright and dark depending on their background. These changes in brightness bring frogs closer to their immediate environment, which consists mostly of green leaves. We also found that the legs are more transparent than the body so that when the legs are held tucked to the side of the frog at rest, this creates a diffuse gradient from the color of the leaves to the color of the frog rather than the sharp edges that stand out more. This suggests a new form of camouflage: ‘edge diffusion’. “
Barnett says scientific debate is often skeptical about the extent to which glass frogs can be called transparent.
“Transparency is, at face value, perfect camouflage. This is relatively common in aquatic species where animal tissue has the same refractive index as the surrounding water. However, air and tissue are very different in their refractive index, so transparency is predicted to be less effective in terrestrial species. Indeed, terrestrial examples are rare. Although glass frogs are one example of terrestrial transparency that is often cited, their rare green pigmentation means they are better described as translucent, “Dr. Barnett said.
Barnett’s Ph.D. mentored by Professor Nick Scott-Samuel, an expert in visual perception from the Bristol University School of Psychology, and Innes Cuthill, Professor of Behavioral Ecology from Bristol’s School of Biological Sciences. Professor Scott-Samuel said:
“Our study addresses questions that have been the topic of much speculation, both among the public and the scientific community. We now have good evidence that the appearance of glass-like frogs, indeed, is a form of camouflage.”
Professor Cuthill said: “Animal camouflage has long been an example of a textbook about the power of Darwin’s natural selection. But, in fact, we have only begun to reveal how different forms camouflage actually works. Glass frogs illustrate a new mechanism that we have never considered before. ”
James B. Barnett et al., “Imperfect transparency and camouflage in a glass frog,” PNAS (2020). www.pnas.org/cgi/doi/10.1073/pnas.1919417117
Scientists see through camouflage through glass frogs (2020, May 25)
taken May 25, 2020
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