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The mantis shrimp begins to practice its strokes at just 9 days old

The fastest new blows in the animal kingdom probably belong to the mantis shrimp and may begin to trigger these attacks just over a week after hatching, when they have just started hunting prey, according to a new study.

For the first time, researchers looked through the transparent exoskeletons of these young mantis shrimp to see the internal mechanisms of their powerful moving weapons, according to researchers online on April 29 in the Journal of Experimental Biology. The findings allow scientists to go into hidden details of how these rapid armaments work.

Mantis shrimp are equipped with special pairs of arms that can explode with bullet accelerations to hit at speeds of approximately 110 miles per hour. Previously, scientists deduced that these weapons act like crossbows. When a latch holds each arm in place, the arm muscles contract, storing energy inside the arm hinge. When crustaceans release these latches, all this energy discharges at once (SN: 8/8/19).

But researchers did not know at what age the mantis shrimp first begins to launch these spring attacks. Computer simulations predicted that armaments could be accelerated the smaller they were suggested, suggesting that the young mantis shrimp could have faster weapons than adults, says Jacob Harrison, a marine biologist at Duke University.

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To solve this mystery, Harrison and colleagues collected a series of microscopic creatures in the docks of boats on Oahu, Hawaii, sifting larvae of Philippine mantis shrimp (Gonodactylaceus falcatus) about the size of rice grains. They then stuck the larvae on toothpicks to record their blows in a high-speed video. The researchers also captured an egg-laying of the species and raised the young for 28 days to see how the anatomy of their weapons developed over time.

A larval mantis shrimp (Gonodactylaceus falcatus) – filmed at 2,000 frames per second and reproduced at 3 percent speed – retracts and locks the attack arm to store energy before launching a blow. New research shows that these larvae begin to unleash their shocks when they are 9 days old.

As soon as nine days after hatching, the larvae began to strike rapidly. His blows flew out at speeds of about 1.4 miles per hour. Given its small arms – up to about 100 times shorter than those of an adult – that’s comparable to the stroke speed of an adult shrimp, Harrison says. Most importantly, it is up to 10 times the swimming speed of crustaceans and fish more or less larger than the larvae and more than 150 times that of the young brine shrimp that the researchers fed. These weapons emerged when mantis shrimp larvae begin to feed on live prey, after depleting the yolk sacs with which they were born, Harrison says.

“Mantis shrimp larvae are able to move incredibly fast for something so small,” Harrison says. "It's hard for small things to move fast: muscles and body are so small that there's really no time or space to increase speed."

black and white image of a mantis shrimp larvaAt 11 days old, this mantis shrimp larva (Gonodactylaceus falcatus) has already developed an appendage (bent under the eye) capable of ultrafast strokes that were previously only seen in adults.Jacob Harrison

Mantis shrimp may need these limbs fast when they are young “because of the water in which they live,” Harrison says. Water feels more viscous for small creatures than for larger ones, so moving through it can be challenging for microscopic larvae. However, its powerful appendages can overcome this drag to catch prey, he points out.

Contrary to what the researchers expected, the larvae were no faster than the adults. For example, during strokes, the larvae rotated their arms at speeds of about one-third to half those of the adult turkey mantis shrimp. These findings suggest that there may be some restrictions on these weapons in these microscopic sizes that more research may uncover, Harrison says.

Alternatively, the larvae simply don’t require faster weapons than those of adults: “they just need a crossbow to work and they don’t need it to be this superpowered fool,” says invertebrate neuroecologist Kate Feller at Union College in Schenectady, New York. , who did not participate in this investigation.

The most amazing part of this job, Harrison says, was how he and his colleagues could peek inside the glassy bodies of the larvae to see how the muscles behaved during a blow, something previously only imagined from surgical dissections and CT scans.

“The fact that these larvae are transparent is a great opportunity to answer questions like how the latch works,” Feller says. "That's very exciting."

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