How butterflies trick predators

THE UNIVERSITY OF MELBOURNE

Butterflies use a trick known as Müllerian mimicry - imitating other species with an equally unpleasant taste. Image: Laurentius/iStockphoto A century old mystery has been solved by a new study showing how butterflies mimic the wing patterns of other species to escape being eaten by birds. The study is published today in the international journal Nature. Dr Siu Fai (Ronald) Lee from the Department of Genetics and Bio21 Institute, University of Melbourne, travelled to the UK to join the research team, led by scientists at CNRS (Muséum National d'Histoire Naturelle, Paris) and the University of Exeter (UK). Researchers studied the Amazonian butterfly Heliconius numata to understand how it imitates other species with an equally unpleasant taste. This trick is known as Müllerian mimicry; a predator that has learned to avoid an organism with certain markings, will avoid all similar-looking species. “Charles Darwin was puzzled by how butterflies evolved such similar patterns of warning colouration. We have now solved this mystery, identifying the region of chromosome responsible for changing wing patterns,” Dr Lee said. The study identified a single genetic switch known as a ‘supergene’ which allows the insects to morph into several different forms. Different types of this ‘supergene’ correspond perfectly to the most successfully adapted wing patterns found in this species. The group discovered that in nature, these different ‘supergene’ types are achieved by sections of the chromosome flipping in three different combinations. This simple solution allows mimicry factors that work best together to stay together, while preventing combinations that produce non-mimetic patterns from continuing in the population. “It is amazing that by changing just one small region of the chromosome, the butterfly is able to fool its predators by mimicking a range of different butterflies that taste bad. The butterflies rearrange this supergene DNA like a small pack of cards, and the result is new wing patterns. It means that butterflies look completely different from one another, despite having the same DNA. “This is a fascinating adaptive strategy and the genetic solution is surprisingly elegant. The results show that small chromosomal changes can preserve successful gene combinations and help the species to adapt.”