Exeter scientist discovers how the butterflies got their spots

Professor Richard ffrench-Constant of the University of Exeter's School of Biosciences, has worked with scientists from Cambridge University and from the US on this discovery. The study, which was partly the result of work in the genetics laboratory on the University of Exeter's Cornwall Campus, has been published in leading academic journal PLoS Genetics.

Heliconius, or passion-vine butterflies, live in the Americas – from the southern United States to southern South America. Although they cannot interbreed, H. melpomene and H. erato have evolved to mimic one another perfectly.

These delicate butterflies have splashes of red and yellow on their black wings, signalling to birds that they contain toxins and are extremely unpalatable. They mimic one another’s colour and pattern to reinforce these warning signals.

Scientists have studied these butterflies since the 1860s as a classic case of evolution in action, but only now is modern sequencing technology unlocking the underlying genetics.

The team of researchers, which has been breeding the butterflies in Panama for the past decade, has been searching for the genes responsible for the butterflies’ wing patterns and the answer to the question of whether the same genes in two different species are responsible for the mimicry.

Professor Richard ffrench-Constant who is based on the University of Exeter’s Cornwall Campus, said: “Darwin himself wondered why different butterflies have evolved the same colour patterns. Darwin was not even aware of the existence of genes but now we know exactly which genes trigger which colour patterns. This then allows us to understand how the butterflies have evolved to look the same using the same genes - something Darwin could only dream about.
 
“These genes are important and they not only make butterflies look colourful but they are also the key genes that enable the butterflies to signal to birds that they are nasty to eat.”

These butterflies have been studied since Darwin’s day because they are such a striking example of adaptation. For years, scientists have pondered whether when different species evolve to look the same, they share a common genetic mechanism.

Because there are thousands of genes in the butterflies’ genome, most scientists felt it was unlikely that the same genes should be involved. But the results of this study suggest that this is, in fact, the case.

The next stage of the research is to look at other traits, such as behaviour, because the butterflies have preferences for particular colours and use wing patterns to select mates.