The University of Queensland Queensland Brain Institute’s (QBI) Dr Yakir Gagnon said the team had already shown that mantis shrimp (Gonodactylaceus falcatus) could reflect and detect circular polarizing light.
“This is extremely rare in nature and, until now, no-one has shown what they use it for,” he said.
“This study shows that the shrimp use circular polarization as a means to covertly advertise their presence to aggressive competitors.”
QBI’s Professor Justin Marshall, who heads the Australian part of the polarization team, said it was more common for animals to communicate with color.
“In birds, coloured feathers advertise gender and territory and in the ocean, reef fish display with colour – this is a form of communication we almost understand,” he said.
“What we’re now discovering is that there’s a completely new language of communication. “Linear polarized light oscillates in only one plane, whereas circular polarized light travels in a spiral – clockwise or anti-clockwise – direction.
“We’ve now determined that mantis shrimp display circular polarized patterns on the body, particularly on the legs, head and heavily armored tail, which are the regions most visible when they curl up during conflict.
“These shrimp live in holes in the reef and they like to hide away. They’re secretive and don’t like to be in the open.”
Dr Gagnon said that researchers dropped a mantis shrimp into a tank with two burrows to hide in – one reflecting unpolarized light and the other reflecting circular polarized light.
“We found that the shrimp chose the unpolarized burrow 68 per cent of the time – suggesting the circular polarized burrow was perceived as being occupied by another mantis shrimp,” he said.
“If you essentially label holes with circular polarizing light, by shining circular polarizing light out of them, shrimps won’t go near it.
“They know – or they think they know – there’s another shrimp there.”
Professor Marshall said the findings could help doctors to better detect cancer.
“Cancerous cells do not reflect polarized light, in particular circular polarizing light, in the same way as healthy cells,” he said.
“Cameras, designed by our US collaborators in Washington University in St Louis under Associate Professor Viktor Gruev, have been equipped with polarizing sensors inspired by mantis shrimps and may detect cancer cells long before the human eye can see them.”
Professor Marshall was also part of a second study with QBI alumni Dr Martin How, which showed that linear polarised light was used as a form of communication by fiddler crabs. “These animals seem to have evolved in-built sun glasses to help them survive and communicate on the mudflats,” he said.
Both the mantis shrimp study and the fiddler crab study are available online in the journal Current Biology.
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