Crustacean Color Control System Decoded

Anna Salleh, ABC Science Online

July 28, 2009 -- Popular crustaceans like lobsters, crabs and prawns owe their success to a unique color control system, according to a new genetic study.

Australian zoologist Nick Wade of the CSIRO Food Futures Flagship in Brisbane and colleagues reported their findings in this week's issue of the journal Molecular Biology and Evolution.

"We identified that this particular coloration system is only found in crustaceans," said Wade. "It's not found anywhere else in the animal kingdom."

Wade researched the crustacean color system for his PhD while at the University of Queensland and the Australian Institute of Marine Science.

Most people like their lobsters, crabs and prawns to come in nice strong colors because this is a sign the animals are good quality, said Wade.

"If the animal was all white people wouldn't be willing to pay much for it," he said.

But, said Wade, for crustaceans their color is key to their survival because it enables them to camouflage themselves and communicate with mates.

Scientists have long known that central to the color system of crustaceans is the carotenoid pigment astaxanthin, present in the shells of the animals.

A protein called crustacyanin is known to bind to astaxanthin and twist the pigment in various ways, changing the wavelength it reflects from red to a whole spectrum of colors, depending on how the molecules interact.

When a lobster is cooked, the crustacyanin protein is destroyed and the color of the shell returns to the orange of the free carotenoid.

The interaction between astaxanthin and crustacyanin is behind the myriad of colors that adorn various lobsters and prawns, said Wade.

"We're talking about going from the red end of the spectrum to the blue end of the spectrum," he said.

"That's the entire length of the visible spectrum. This protein is able to do something that no other protein can do."

Wade and colleagues wanted to know how widespread this color system is in the animal kingdom.

They looked for the gene responsible for crustacyanin in a whole slew of different animals but could only find it in crustaceans.

Wade said this simple "one molecule, many colors" system could have been key to the success of crustaceans, which occupy a bewildering diversity of habitats.

"What we're doing is starting to identify the genetic basis of biodiversity," he said.

Apart from genetics, other factors that influence the color of crustaceans are their dietary intake of carotenoids and the background color of their environment, said Wade.

Wade added that in the future the crustacean system could be used to develop new food dyes.

It could also be used to develop new indicators of acidity and temperature since both these factors can affect the protein-pigment complex, and thus affect color.

"You could engineer the protein to do more than it used to do," he said.

http://dsc.discovery.com/news/2009/07/28/crustacean-color.html