Scientists uncover mimicry mystery
A European team of researchers has discovered why butterflies have the capacity to change their wing patterns to mimic neighbouring species and ensure their survival from bird attacks. Published in the journal Nature, the study pieces together the puzzle that has intrigued scientists for so many years, Darwin included. The findings bring to light how genomic rearrangements can play a key role in the co-existence of adaptive phenotypes involving various genes working together, by limiting recombination and gene flow. Some of the world's leading evolutionary thinkers have speculated on how butterflies that are distasteful to birds have evolved the same patterns of warning colouration. Researchers from the Muséum national d'Histoire naturelle, Paris (Centre National de la Recherche Scientifique, CNRS) in France and the University of Exeter in the United Kingdom provide insight into the ruse used by butterflies to trick birds. Termed Müllerian mimicry, this natural phenomenon occurs when two or more species that share common predators mimic each other's warning signals. Investigating the Amazonian species Heliconius numata which mimics a number of other butterfly species at a single site in the rainforest, the team says a population of the species has distinctive wing colour patterns that resemble those of other butterflies, such as the genus Melinaea, which birds find foul to eat. This neat trick keeps butterflies safe from their predators. The team identified and sequenced the chromosomal region responsible for the wing patterns in H. numata. A single region on a single chromosome controls the butterfly's wing pattern; the chromosome contains genes that control the pattern's varied elements. The clustering, what experts call the 'supergene', enables genetic combinations that are 'favoured' for their mimetic resemblance to be maintained. But is also ensures that combinations that generate non-mimetic patterns do not emerge. Supergenes are crucial for the development and maintenance of various features found in the natural world, including the colours and patterns of marine creatures and the shapes of flowers. In their study, the researchers discovered that three versions of the same chromosome co-exist in this species, and that each version controls distinct wing-pattern forms. So butterflies can look very different but share the same deoxyribonucleic acid (DNA). 'We were blown away by what we found,' says lead author Dr Mathieu Joron of the Muséum national d'Histoire naturelle. 'These butterflies are the "transformers" of the insect world. But instead of being able to turn from a car into a robot with the flick of switch, a single genetic switch allows these insects to morph into several different mimetic forms - it is amazing and the stuff of science fiction. Now we are starting to understand how this switch can have such a pervasive effect.' Commenting on the research findings, Professor Richard ffrench-Constant of the University of Exeter, says: 'This phenomenon has puzzled scientists for centuries - including Darwin himself. Indeed, it was the original observations of mimicry that helped frame the concept of natural selection. Now that we have the right tools we are able to understand the reason for this amazing transformation: by changing just one gene, the butterfly is able to fool its predators by mimicking a range of different butterflies that taste bad.' Concerning the supergene region, Professor ffrench-Constant points out that it is 'a gene that really packs an evolutionary punch'.For more information, please visit:Muséum national d'Histoire naturelle:http://www.mnhn.fr/museum/foffice/transverse/transverse/accueil.xsp?cl=enUniversity of Exeter:http://www.exeter.ac.uk/Nature:http://www.nature.com/
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France, United Kingdom