For a scuba diver, one of the best underwater sights is a rock face covered in brilliantly coloured jewel anemones (Corynactis viridis). They exist in many colours, and often vivid, contrasting colours are found side by side. There are also subdued, semi-transparent variants. Most species of wild animals have evolved to just one or a narrow range of colours, while flowers can have a range of vivid colours, presumably to attract a variety of insects. As far as I know, the anemones aren鈥檛 trying to attract their prey 鈥� it just arrives on the current. So why are they so vivid and so varied?
鈥� My colleague Anya Salih and I have worked on this question for some time in corals, which are close relatives of sea anemones. We believe that the pigments have a protective function against excess light, as discussed in our paper 鈥溾��, which appeared in Nature, vol 408, p 850 ().
Unpigmented as well as pigmented versions exist in both corals and anemones. The explanation for this is probably that the production of pigments is 鈥渃ostly鈥�, and pigmented versions cope by being fitter than their unpigmented cousins. When conditions are unfavourable the coloured ones do better, though favourable and poor conditions are both common enough that neither form takes over.
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Some controversy over this interpretation remains, although we are still waiting for someone to come up with something better.
Guy Cox, Electron Microscope Unit, University of Sydney, New South Wales, Australia