Discover the fascinating story behind the independent origins of frog glue, a remarkable defense adaptation that has evolved multiple times in amphibians. Explore the intricate molecular mechanisms that make this sticky secretion an effective predator evasion tool, and learn how it could inspire new advancements in rapid-acting adhesive technologies.
Why This Frog Glue is a Sticky Problem
Consider a moment from your wildest dreams when some slimy residue from the skin of the frog pours out in large quantities between your finger locking your hands together. Resulting from this incredible defense adaptation found in only very few amphibians, is the bizarre but true phenomenon known as frog glue.
These frogs secrete a thick fluid from their skin which then hardens very quickly as soon as it is expressed and swallowed by any potential predator. C tomentosum has been well-dubbed the “transglutaminase-glue,” as this adhesive is not only an interesting anecdote, but also a remarkable glimpse at just one of apparently numerous independent acts of evolution by which amphibians have evolved similar unique adaptations for defense.
Deciphering the chemistry behind frog glue
In a long-term study to examine the origin and characteristics of frog glue, researcher Shabnam Zaman and colleagues studied the glue produced by the tomato frog, Dyscophus guineti, the only species of member of Malagasy frogs. By combining functional, molecular and evolutionary analyses they also discovered two proteins that act in concert to provide the frog glue with its exceptional adhesive and cohesive properties.
PrIT is a huge glycoprotein that is believed to have very specific attraction for glue. Ubiquitination is a phosphorylated ubiquitin- binding an evolutionarily conserved domain that many extracellular metazoan proteins have multiple copies of. The second is a member of the widespread galectin family, which are small glycan-binding proteins. The presence of these glycoproteins and glycan-binding proteins is in agreement with what we know is common to other animal glues, but how they work had not been previously understood.
Additional analysis indicated that the structural flexibility of the frog glue PRIT protein enables it to change shape according to any surface touch, even those formed by a predator’s oral epithelia. This pressure-sensitive behavior is crucial to how it changes from a runny goo into a strong, quick-setting glue upon being disturbed by an attacker (e.g., biting).
Conclusion
The parallel evolution of defense mechanisms in amphibians is brilliantly illustrated by frog glue. A secretion like the one associated with Dyeing poison dart frogs is also used by unrelated frogs to frighten off predators — man itself or another animal — each of these additional lineages collecting an evolutionary debt for recruiting the same pre-existing genes and then stepping on the pedal so to speak of their expression. The study not only helps explain how these exotic adaptations are possible, but also offers a pathway to rapid-acting adhesives that might be useful in surgery. The humble frog, as we continue to shine light on the mysteries of the natural world, may very well be the thing that creates this generation’s next great adhesive.
