Writer: Lava Naz Bagdu
Chameleons and octopuses are frequently celebrated for their exceptional camouflage abilities, but there's a lesser-known contender in the camouflage competition: the remarkable glass frog. These tiny creatures blend into their surroundings extraordinarily with their translucent underbellies, revealing a glimpse of some internal organs –a fascinating adaptation for survival. In this article, we are not only going to explore their general features but also delve into the biology behind the translucent body and the scientific studies about it.
General Features of Glass Frogs
Glass frogs are a group of amphibians found in the family Centrolenidae. These species fall within 12 different genera (Centrolene, Cochranella, Espadarana, Hyalinobatrachium, Ikakogi, Nymphargus, Rulyrana, Sachatamia, Teratohyla, Vitreorana, Chimerella, and Celsiella). Most of the species are classified in the genera Centrolene, Cochranella, and Hyalinobatrachium. Generally, the adults are notably small ranging from 20 mm to 30 mm (0.8 to 1.2 inches) in total length while in some species, they’re larger reaching a maximum of 80 mm (3 inches).(Zug, 2024; Ifaw, 2024)
While observing a glass frog, an observer can see the heart pumping blood to the arteries, or food moving through the esophagus and the digestive system. The exact reason behind this translucency is not fully understood, however, it is generally thought to aid in camouflage and hiding from predators. One notable study, “Imperfect Transparency and Camouflage in Glass Frogs” led by James Barnett and colleagues in 2020, provides strong evidence that the imperfect transparency (translucency) helps change the luminance of the frog with the immediate background, lowering detectability and increasing survival when compared to opaque frogs. (Zug, 2024; Barnett, et. al., 2020)
Based on these findings, in another study named“Glass frogs conceal blood in their liver to maintain transparency” which was led by Jesse Delia and her colleagues, the researchers found that when in the resting phase, the glass frogs increased their transparency two to threefold by removing 90% of the red blood cells from the circulation and segregating them within their liver, which contains reflective guanine crystals that shield the cells from light. This process was observed using a technique called photoacoustic imaging at Duke University. (American Museum of Natural History, 2022; Delia, et. al., 2022)
“In most vertebrates, aggregating red blood cells can lead to potentially dangerous blood clots in veins and arteries. But glass frogs don’t experience clotting, which raises significant questions for biological and medical researchers.” (American Museum of Natural History, 2022; Delia, et. al., 2022)
A Glass frog photographed while asleep (left) versus in an active state (right) (amnh.org)
Photoacoustic Imaging
Photoacoustic imaging (PAI) also called optoacoustic imaging is an advanced, biomedical modality based on the use of laser-generated ultrasound with traditional, optical imaging to create detailed imaging of biological tissues and molecules such as red blood cells. It works by using pulses of laser light that are absorbed by the tissues causing a small amount of heat. This heat causes the tissues to expand slightly and generate sound waves (ultrasound). These sound waves are then detected and converted into an image. (Beard, 2011)
Photoacoustic image of a glass frog under anesthesia (pratt.duke.edu)
Conclusion
In conclusion, the glass frogs’ translucency and camouflage skills, a product of natural selection, continue to intrigue scientists. While studies continue to explore the exact reason behind it, most suggest that it serves as a defense mechanism to evade predators with camouflage as previously mentioned in this article. Despite their fascinating adaptations leading to a remarkable appearance, these creatures are under the threat of extinction, and many species of glass frogs are now endangered. Although deforestation and human intervention have pushed them to the brink of extinction, almost nothing is being done to protect them. Shockingly, some people are unaware of their name and even existence let alone the crisis they face. Without immediate action, we are at risk of losing these unique creatures before the world even becomes aware of their existence. Their survival depends not only on their adaptations but also on human awareness and actions to prevent them from becoming extinct before it’s too late.
References
Zug, G. R., glass frog, Britannica, (2024.09.20)
Glass Frogs, Ifaw, (2024.09.20)
Barnett, J. B., Michails, C., Anderson, H. M., McEwen, B. L., Yeager, J., Pruitt, J. N., Scott-Samuel, N. E., Cuthill, I. C., (2020), Imperfect transparency and camouflage in glass frogs, PNAS
Glass frogs Hide Red Blood Cells in Liver to “Disappear”, (2022), American Museum of National History
Delia, J., Taboada, C., Chen, M., Ma, C., Peng, X., Zhu, X., Jiang, L., Vu, T., Zhou, Q., Yao, J., O’Connell, L., Johnsen, A. S., (2022), Glass frogs conceal blood in their liver to maintain transparency, Science.
Beard, P., (2011), Biomedical photoacoustic imaging, National Library of Medicine
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