24 August 2018
Not all of us can click our fingers in the air, let alone underwater – but several kinds of shrimp can snap their claws to make a seriously loud sonic burst! Snapping shrimps actually have just one big, noisy claw, along with one much smaller one.
The shockwave produced helps them catch prey, and the sound may be used for communicating and attracting mates. They make a cacophony of noise together amongst coral reefs and rocks.
New research suggests that the various shrimp species have evolved their snapping abilities separately, not from a common ancestor that kept on snapping as its progeny evolved over time, but more likely through some chance events (such as genetic mutations) that led to several different species making the same loud noise.
The mechanics of these shrimp species’ claws have been studied before to work out how the sounds are made. The claw snaps shut with such force that it creates a vacuum bubble – not air-filled, just empty space – which makes an explosive bang as water then refills it.
The claw mechanism is quite complex, using a ratchet and lever system together with specialised muscles. In a study published in Current Biology, researchers found that the shrimps started off, in evolutionary terms, with ancestors with quiet joints (one type called ‘slip’, then another called ‘torque reversal’ joints).
These developed separately (in palaemonid species, and some members of the family Pasiphaeidae), to the noisy, snapping joint forms, but only after the shrimps had already become distinctly separate species.
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