Natures wonders: venus flytrap new studies (Introduction)

by David Turell , Tuesday, July 09, 2019, 23:27 (1962 days ago) @ David Turell

How does it trap something as light as a mosquito? Deforming trap hairs set off electrical impulses:

https://phys.org/news/2019-07-carnivorous-mosquitoes.html

"The plant is capable of sensing prey through delicate trigger hairs on the inside of its flat leaves. Since prey insects come in different sizes and the Venus flytrap cannot afford to be fussy, the plant grows traps across a variety of sizes.

"Now, researchers from the universities of Würzburg and Cambridge have discovered that the tactile sensors in these traps already respond to minute pressure stimuli, converting them to electrical signals that cause the trap to close.

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"'Each trap lobe features three to four multicellular hairs that are torsion-resistant except for a notch at the base. When an insect, lured by the smell, color or nectar of the trap, touches the trigger hair, the hair will yield in the area of the non-reinforced base. This causes the sensory cells in this area to be stretched on one side and compressed on the other side," says Professor Rainer Hedrich, explaining the operating principle of the Venus flytrap.

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"An ant or housefly creates a force when walking which is approximately equivalent to its body weight. So a fly weighing ten milligrams is capable of generating 100 micronewtons, a force that is easily sufficient to excite a large trap. However, if a mosquito weighing just three milligrams ends up in such a large trap, the trigger hairs will not be deflected.

"But since a mosquito, too, can be an important source of nutrients, the Venus flytrap has also developed smaller traps during the course of evolution. These mini-traps also respond to the smaller forces generated by the lightweight mosquito. "This trap-size-based sensitivity of the trigger hairs is crucial for the economic efficiency of the traps," Professor Hedrich explains. After all, it costs the plant much more energy to reopen a large trap than a small one. "If underweight, low-nutrient prey insects were able to trigger large traps, the cost-benefit ratio would turn out negative and the Venus flytrap would slowly starve in the worst case," Professor Hedrich explains. (my bold)

"Once the trap has closed, the insect prey usually does not just accept its fate. Instead it struggles and tries to escape. In its panic, it constantly touches the tactile hairs, triggering up to 100 action potentials in two hours. According to Professor Hedrich, the Venus flytrap takes into account these electrical signals and initiates a corresponding response that ranges from the production and excretion of digestive enzymes to taking up the nutrients from the decomposed prey.

"The scientists conducted another experiment to determine how often a single trigger hair can be stimulated within one hour. The result: "From a frequency of a tenth of a hertz, that is one stimulation every ten seconds, the trigger hair starts to exhibit signs of fatigue," says Sönke Scherzer. At higher frequencies, an action potential was no longer triggered each time a tactile hair is stimulated and eventually the electrical events did not take place at all. When the scientists interrupted the repeated stimulation sequence for a minute, the hair fully regained its mechano-electrical properties."

Comment: Note the bolded paragraph. The explanation for tiny traps makes sense, but it is impossible to imagine how evolution evolved such a complex plant .