28 July 2009

How do crustaceans get their colours?

All crustaceans get their colours by eating a small molecule known as a carotenoid. Carotenoids occur widely in nature: in photosynthetic bacteria, algae and plants such as carrots and capsicums.
Reticulated moon crab (Matuta planipes)
Crustaceans have a protein called crustacyanin that modifies the red carotenoid wavelength to other colours.
Blue-tail prawn
The coloured protein complex can be easily disrupted. This is why prawns, crabs or lobsters turn red when they are cooked. The original red carotenoid is released.
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How lobsters create their colours
Fresh Science 26 Jul 09;
A team of Queensland researchers have discovered that lobsters, prawns and other crustaceans have evolved a unique way of making colours: making the complex patterns appreciated by biologists and connoisseurs of seafood.

Their work will help with conservation, aquaculture and may even lead to a new food colourant. And all the colours come from just one molecule.

The colour of seafood is directly linked to its acceptability as food. Highly coloured lobsters and prawns attract a premium price. And for the crustaceans themselves, it’s a matter of survival.

So, whether you are working in the world’s US$38-billion crustacean fisheries or part of the catch, the work of Dr Nick Wade and colleagues at the University of Queensland (UQ) and Australian Institute of Marine Science (AIMS) is significant. They have identified the underlying genetics that explains the way in which crustaceans produce their wide range of shell colours. Their research was published this week in the Journal of Molecular Biology and Evolution.

“This knowledge of how crustaceans produce and control colour helps us understand the genetic diversity and evolution that underpins this group of highly successful group of animals,” Nick says, “as well as benefit the future development and sustainability of the aquaculture industry.”

In order to be coloured, all crustaceans must consume the same small molecule known as a carotenoid. They occur widely in nature: in photosynthetic bacteria, algae and plants such as carrots and capsicums.

Crustaceans use the bright red carotenoid astaxanthin bound to a protein, called crustacyanin. This protein modifies the carotenoid wavelength to any other colour in the visible spectrum. “Apart from crustaceans, no other animals we analysed had the crustacyanin gene”, says Nick. “Therefore, we now know that crustaceans have evolved a unique way of using this simple carotenoid building block to produce all their colours”, he says.

“This protein is used only by crustaceans to create their intricate and diverse shell colour patterns”, says Nick, “providing protective camouflage or communication which, in turn, may have contributed to the success and diversification of their group”. But the coloured protein complex can be easily disrupted, as we see when we cook prawns, crabs or lobsters, and the original red carotenoid is released producing the colour we associate so strongly with cooked seafood.

When bound to protein, the normally fat soluble carotenoid also becomes strongly water soluble, providing a potential application for these compounds as natural food colourants. Other uses could include coloured heat or pH indicators.

Reference: Nick Wade, Alina Tollenaere, Mike Hall and Bernard Degnan, Evolution of a novel carotenoid binding protein responsible for crustacean shell color, Molecular Biology and Evolution, published August, 2009. This research was conducted as part of an Australian Research Council Linkage grant.

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