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Promiscuous butterflies speed up evolution

Hybrid butterflies Different species of butterflies speed up the evolution of biodiversity by interbreeding so they can share genes for protective wing patterns, say researchers.

The international consortium report their findings today in the journal Nature.

"It would be a lot faster than waiting around for a mutation," says team member Evolutionary geneticist, Dr Durrell Kapan of the California Academy of Science.

Scientists study butterflies to get insights into ecology and evolution because the insects have fast generation times and very colourful and conspicuous variation in form and function.

Their brightly coloured wing patterns are visual stop signs that warn predators to stay clear because the butterflies are toxic.

In the late 1800s, German biologist Fritz Müller, discovered the wing patterns of a particular species of butterfly in the Amazon could change according to its geographic location.

Not only that, but he found other species of that genus had the exact same protective wing pattern when it was in the same location.

Kapan and colleagues investigated the genetic basis of this mimicry.

Genome study

The central star of their research was the Postman Butterfly (Heliconius melpomene), which is from Central and South America and has many different races, which inhabit different locations and have their own distinct wing patterns.

The researchers compared the genome of different races of H. melpomene and various species that mimicked its wing pattern.

They found species distantly related to H. melpomene had independently evolved to produce the same protective wing pattern, in a case of 'convergent evolution'.

But other mimicking species had actually obtained the genes for their protective wing pattern by mating with H. melpomene - something they were able to do because they were closely related.

Hybrids produced as a result of breeding between species normally results in less healthy offspring, but when it results in the transfer of beneficial traits it can bring an evolutionary advantage.

"The successful hybrids were the ones that looked like Heliconius melpomene," says Kapan.

This phenomenon is referred to as "adaptive introgression", says Kapan.

He says this process could lead to the spread of protective wing patterns between species within several generations rather than over thousands of years - the time it would take for mutations to arise and be acted on by natural selection.

"Evolution can occur much more rapidly if species share genes which are adaptive," he says.

'Very exciting' research

Australian geneticist Dr Siu Fai Lee of the University of Melbourne who has also researched Amazonian butterfly genetics describes the research as "very exciting".

He says sharing genes, also known as 'horizontal gene transfer', is common between genetically distinct microbes but there hasn't been enough research to see how widespread it is in animals.

Sharing genes says Lee is a convenient solution to adaptation.

"If you are in danger and you need a genetic solution it's best to steal genes from your cousin rather than waiting for the slow process of genetic mutation," he says.

Lee says zoos often hybridise genetically distinct animals in the hope of introducing genes that will make captive animals more healthy.

But, he says introgression can be more effectively for conservation once beneficial genes are identified.