Enlarge /. A new study shows that Mantis shrimps don't hit quite as hard when they're not in the water.
The Mantis shrimp is known in the animal kingdom for its fast, powerful hammer blow, which is in no way inferior to the force of a .22 caliber bullet. One could conclude that these strikes in the air would be even faster and more powerful given the lower density and the lower air resistance of the medium. However, according to a recent article in the Journal of Experimental Biology, this is not the case. Rather, scientists found that the animal strikes the air at half the speed, suggesting that the Mantis shrimp can control its striking behavior precisely depending on the surrounding medium.
Mantis shrimp come in many different types: around 450 species are known. But they can generally be divided into two types: those who stab their prey with spear-like attachments ("spears"), and those who smash their prey ("smashers") with large, rounded and hammer-like claws ("raptorial attachments") "). These blows are so fast – up to 23 meters per second or 51 miles an hour – and powerful that they often create cavitation bubbles in the water and create a shock wave that can act as a follow-up strike, stunning and sometimes killing the prey. Sometimes A blow can even produce sonoluminescence, with the cavitation bubbles producing a brief flash of light when they collapse.
According to a study from 2018, the secret of this powerful blow does not seem to be in bulky muscles, but in the spring-loaded anatomical structure of the arms of the shrimp, which resembles a bow and arrow. The muscles of the shrimp pull on a saddle-shaped structure in the arm, causing them to bend and store potential energy that is released when the club-like claw swings.
Kate Feller, co-author of the latest study, which is now being conducted at the University of Minnesota, had previously conducted a physiological study of Mantis shrimp in the laboratory at the University of Cambridge in the UK. The creatures really don't like these controlled conditions and tend to strike, especially when exposed to the air. Feller now found out how to keep the shrimp so that their gills stayed under the water, even though the limbs they were beating with were exposed to the air. Her Cambridge colleague and co-author Greg Sutton visited her laboratory one day and mentioned in passing that it might be interesting to measure the force of the shrimp's hammer blows in the air. And so this latest study was born.
Enlarge /. Mantis shrimp firing their hammer blows in the air and water.
Feller and her team experimented with six female and one male Mantis shrimp. In order to control every change in posture, each shrimp was partially held on a gimbal platform in an aquarium partially filled with sea water. In this way the animals were brought into the aquarium, sometimes completely submerged, sometimes partially.
The scientists then carefully pricked each rear shrimp with a fiber optic rod to hit them defensively while recording the movement using high-speed video. And no, the shrimp didn't appreciate being poked. "I have a pretty epic photo of my bleeding hand over a white sink when someone stabbed me during the process," said Feller.
The team analyzed a total of 31 strikes in the air and 36 strikes in the water. Feller had expected the blows in the air to be as strong, if not stronger, but the analysis showed the opposite. The strikes were half as fast and averaged 5 meters per second. In fact, Feller et al. In their work it was found that the kinetic energy release of the Mantis shrimp in air is similar to that of a leg of a grasshopper, while the shrimp could reach ten times the force when struck in water.
Our little Kablammo conversation
Why could this be the case? Feller et al. I think it could be related to the need for some kind of shock-absorbing ability, and suggests that the limbs of grasshoppers and similar jumping insects have built-in structures to absorb excess kinetic energy. A 2012 study found that the Mantis Shrimp Claw also absorbs energy well thanks to an inner layer of chitin (often found in crustacean shells), calcium phosphate (found in human bones) and calcium carbonate. Work from the same group in 2016 found that the outer layer of the claw also contained chitin fibers surrounded by calcium phosphate arranged in a precise herringbone pattern.
Admittedly, part of the excess energy is also released into the target – such as hard snail shells. However, this latest study shows that the medium could also contribute to shock absorption. "The surrounding medium and the impact target work together as external shock absorbers for Mantis shrimp blows," the authors wrote.
In other words, maybe water can better dissipate the excess kinetic energy generated by the punches, so the shrimp do not have to pull their punches as much as when punching in the air. "Not only are the forces of drag from the water missing in the air, but the entire sensory experience is mixed up," said Feller. "Perhaps, in the absence of a perceived goal, the animals won't give him the full force so that they don't blow out their joint."
DOI: Journal of Experimental Biology, 2020. 10.1242 / jeb.208678 (About DOIs).