Natures wonders: amazing frog tongue (Introduction)

by David Turell , Wednesday, February 08, 2017, 15:35 (2843 days ago) @ David Turell

Along with the complex actions of the saliva, the tongue itself is extremely fast in its movements and it is stickier than any of our sticky inventions:

https://cosmosmagazine.com/biology/the-frog-tongue-is-a-high-speed-adhesive?utm_source=...

"The versatile frog tongue can grab wet, hairy and slippery surfaces with equal ease. It does a lot better than our engineered adhesives – not even household tapes can firmly stick to wet or dusty surfaces. What makes this tongue even more impressive is its speed: Over 4,000 species of frog and toad snag prey faster than a human can blink. What makes the frog tongue so uniquely sticky? Our group aimed to find out.

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"biomechanics researchers Kleinteich and Gorb were the first to measure tongue forces in the horned frog Ceratophrys cranwelli. They found in 2014 that frog adhesion forces can reach up to 1.4 times the body weight. That means the sticky frog tongue is strong enough to lift nearly twice its own weight. They postulated that the tongue acts like sticky tape or a pressure-sensitive adhesive – a permanently tacky surface that adheres to substrates under light pressure.

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"Thoroughly intrigued, we wanted to understand how the sticky tongue holds onto prey so well at high accelerations. We first had to gather some frog tongues. Here at Georgia Tech, we tracked down an on-campus biology dissection class, who used northern leopard frogs on a regular basis.

"The plan was this: Poke the tongue tissue to determine softness, and spin the frog saliva between two plates to determine viscosity. Softness and viscosity are common metrics for comparing solid and fluid materials, respectively. Softness describes tongue deformation when a stretching force is applied, and viscosity describes saliva’s resistance to movement.

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"After our tests, we found frog tongues are about as soft as brain tissue and 10 times softer than the human tongue. Yes, we tested brain and human tongue tissue (post mortem) in the lab for comparison.

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"After testing, we were surprised to find that the saliva is a two-phase viscoelastic fluid. The two phases are dependent on how quickly the saliva is sheared, when resting between parallel plates. At low shear rates, the saliva is very thick and viscous; at high shear rates, the frog saliva becomes thin and liquidy. This is similar to paint, which is easily spread by a brush, yet remains firmly adhered on the wall. Its these two phases that give the saliva its reversibility in prey capture, for adhering and releasing an insect."

Comment: Saliva properties were described in other entries, but worth representing since it still presents an amazing set of properties, but the tongue itself seams like no other tongue in catching rapidly moving insects. Again this hunting mechanism is highly complex and is not explained by Darwin stepwise development theory.