Small but mighty: researchers have documented an underwater movement in a representative of the amphipods that is approaching the limits of what is possible. The tiny claws snap shut in less than 50 microseconds, creating a violent movement of water and a bang. Insights into the biomechanical secrets of this performance could also benefit technical developments, say the scientists.
Many natural patents still overshadow human technology – this also applies to the speed of movement. The record holders include insects that can close their mouthparts in a flash. Such extremes are not possible in water due to the higher resistance, but even in this medium, some living beings achieve astonishing achievements. The most famous example are the mantis shrimp, which can strike particularly quickly with their weapons. Now the researchers working with Sheila Patek from Duke University in Durham have been able to document a similar record performance in a much smaller marine animal: Dulichiella appendiculata, which is up to eleven millimeters in size.
Exciting tiny things in sight
Amphipods are a species-rich group of crustaceans whose representatives are native to all oceans and fresh waters. Many of the animals, which are usually only a few millimeters in size, have claw-like structures on their front limbs, which are used for feeding, defense or reproduction. In Dulichiella appendiculata there is a noticeable gender difference in this context: one of the two claws is greatly enlarged in the males. “She makes up a third of her body weight,” says Patek. The movable element of the claw is a “thumb” about one millimeter long, the dactylus, which is about as wide as a human hair. Patek and her colleagues wanted to know exactly what happens when this claw is moved. To do this, they examined some of the tiny things under the microscope and recorded their snapping movements using ultra-high-speed cameras.
The scientists were able to document: The dactyl rushes towards its counterpart in less than 50 microseconds, generating a strong stream of water and a sound. The tiny element achieves a similarly high acceleration as it is known from the weapons of the mantis shrimp, the researchers report. The snapping of the Dulichiella amphipods is now one of the fastest known movements in the underwater world. “The amazing thing is that this performance is exactly at the limit of what we think is possible when it comes to how small something can be and how fast it can move without destroying itself,” says Patek. “If you accelerated even faster, the body structure would break”.
So fast that it bubbles
The researchers also observed that the turbulence caused by the movement sometimes even causes what is known as cavitation: the sudden change in water pressure creates tiny bubbles. “Cavitation is an extremely violent effect. It is one of the most energetic processes on planet earth, ”says Patek. “It is remarkable that these tiny creatures can cause them,” says the researcher.
She and her colleagues now want to further investigate the biomechanics of amphipod claws in further investigations and also investigate the question of what purpose the lightning snap fulfills. “We want to know why the crabs invest so much in these campaigns. Snapping may play a role in male-female interactions or territorial disputes, ”says Patek. The scientists also hope that their research will benefit engineers and developers in the design of moving elements. “You can often discover something in nature that technology has not been able to do before. What makes the designs of evolution so interesting is that life has had millions of years to get it right, ”Patek concludes.
Source: Cell Press, technical article: Current Boiology, doi: 10.1016 / j.cub.2020.12.025
Video: A Dulichiella flea shrimp snaps, triggering the formation of a small bubble. (Credit: Patek Lab)