Eyes and Spots

Scientists have found a mechanism to explain the startling diversity of animal colour patterns.

Scientists have found a mechanism to explain the startling diversity of animal colour patterns.

Adding feather to feather/ For the pride of his eye/ WHAT’S riches to him/ That has made a great peacock/ With the pride of his eye?

Or so WB Yeats had asked. It is more than a rhetorical question. Feather for feather, the peacock is a sight for the eyes, and what is mere wealth for a Being who could make ‘a great peacock with the pride of his eye’? Biologists in their own fashion have struggled with this question. Can their own version of a Being, a creature of Evolution, explain where this patterned diversity of the animal kingdom comes from—the spots and stripes that adorn feather and skin, the eyes on the peacock that so hold our eyes?

Scientists working at the University of Wisconsin-Madison have figured out how North American fruit fly, Drosophila guttifera, generates a complex pattern of 16 wing spots, and in doing so, they have come across a mechanism that is likely to work across species. Sean Caroll, a molecular biologist and one of the authors of the studies, states in a university press release, ‘This is animal colour patterning, how they are generated, how they evolved.’ They started work on the fly which has been little studied, and over three years the genetic manipulation of close to 20,000 fly embryos finally gave them the answer they were looking for. They found that a protein—morphogen coded for by a gene they termed ‘Wingless’, determines the entire process. Late in the development of the embryo, the protein is produced and it then diffuses through tissue. ‘It acts by triggering responding cells to do things, in this case make colour,’ Carroll explains. They also found that the pattern of spots is dictated by pre-existing patterns on the wings, such as intersection of veins or vein crossings. Notes Carroll: ‘The Wingless molecule is deployed in this species at specific points in time and in specific places—the places where the spots are going to be.’

They were able to test their hypothesis by manipulating the gene concerned to produce patterns of their own. “We can make custom flies,” said Carroll, “we can make striped flies out of spotted flies.” And in doing so, they may have found the explanation for the vivid colouring of a butterfly or the pattern of spots on a leopard’s coat.

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