The Tufts team staged fights between shrimp (hastening to add that none of the crustaceans were hurt). But, before the battles began, they applied sunscreen to the meral spots of some of the combatants. That dimmed the spots' UV reflectance.
The scientists found that shrimp whose meral spots had been dimmed suddenly looked like more inviting targets: Their opponents were more willing to ratchet up their aggression against them. This suggested to the researchers that the spots serve as enhanced threat displays. They're meant to back down opponents, in turn helping aggressor shrimp realize they could be defeated if they chose to fight.
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Colors weren't the only thing the scientists blocked for the test battles. By dipping some shrimp's antennae in freshwater for a minute, they also temporarily blocked the ability of some of the shrimp to pick up on chemical signals. With no chemical sensing in their arsenal, the affected shrimp were quick to go near an opponent's refuge and they weren't as aggressive when doing so.
The researchers said chemical signals, then, may provide a tipoff to opponent size and whether or not that opponent is inside its refuge.
"Our experiments demonstrate that [mantis shrimp] use a complex signaling system that combines the UV reflectance of an important spot of color as well chemical cues to help them judge their opponent's state of aggression, fighting ability and the presence of a stomatopod in a refuge," said Amanda Franklin, a Tufts biology PhD student, in a statement.
Franklin and her colleagues' findings have been published in the journal Royal Society Open Science.
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