Evolutionary Novelty in a Butterfly Wing Pattern through Enhancer Shuffling, Richard Wallbank et al. Published: January 15, 2016.
> Butterflies show an amazing diversity of patterns on their wings. In fact, most of the 18,000 species of butterfly can be distinguished on the basis of their wing pattern. Much of this diversity is thought to arise through novel switches in the genome that turn genes on in new contexts during wing development, thereby producing new patterns. Here we study a set of switches that control the expression of optix, a gene that places red patches onto the wings of Heliconius butterflies. We show that two patterning switches —one that produces red rays on the hindwing and the other a red patch on the base of the forewing —are located adjacent to one another in the genome. These switches have each evolved just once among a group of 16 species but have then been repeatedly shared between species by hybridisation and introgression. Despite the fact that they are now part of a common pattern in the Amazon basin, these two pattern components actually arose in completely different species before being brought together through hybridisation. In addition, recombination among these switches has produced new combinations of patterns within species. Such sharing of genetic variation is one way in which mimicry can evolve, whereby patterns are shared between species to send a common signal to predators. Our work suggests a new mechanism for generating evolutionary novelty, by shuffling these genetic switches among lineages and within species. <<
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