Butterfly mimic gene revealed

20 February 2008

Scientists have identified a gene that gives a harmless African butterfly wing patterns like those of toxic species, helping it ward off predators.

Details are reported today in the journal Proceedings of the Royal Society.

Distinct wing colours and patterns, such as the blue wings of the common blue and the two dark dots on the yellow wings of the clouded yellow, identify one butterfly species from another. This is true of most butterflies. The mocker swallowtail butterfly, however, comes in multiple forms, each of them with entirely different wing patterns and colours.  Some of the patterns mimic those of poisonous species and this gives them a valuable disguise to scare off predators.

Biologists have wanted to know how this happens and since the 1950s have thought there must be a genetic 'switch' that controls which wing pattern is expressed in each individual. Until now, however, the location and identity of the genes involved have remained a mystery.  

Finding the genetic code

Professor Alfried Vogler of the Natural History Museum and Imperial College London's Department of Life Sciences and his colleagues, used molecular tags and DNA sequencing to pinpoint the part of the butterfly's genetic code that determines wing pattern and colour.

Their study suggests that a developmental gene called 'invected', which was already known to be involved in the early embryonic development of butterflies, is behind the allocation of different wing patterns in mocker swallowtails.

'We've taken a big step towards identifying exactly how this fascinating insect species is endowed with such a wide variety of extremely useful wing patterns,' says Vogler.

'However, identifying the area of the genome involved in this process is just the first step. We now need to look in more detail at the differences in the invected gene, and another gene located next to it, to find out exactly how they produce the different forms.'

Only the female mimics

The mocker swallowtail, Papilio dardanus, is found in sub-Saharan Africa and has a wingspan of 8.5 -10.5cm. Only females of the species exhibit the wing patterns that mimic other butterflies. All the males are yellow, with black markings and have the typical tails of most swallowtail butterflies.

New light on evolutionary changes

Understanding how these different mimic patterns evolved may shed new light on whether such evolutionary changes occur in small gradual steps, or sudden leaps.

'You could argue that there would be little point in a species which slowly evolved to mimic a poisonous butterfly over the course of generations - the disguise is only useful if full and complete. This could suggest the possibility of sudden leaps in evolution occurring in this species, which would be an incredibly exciting discovery - by studying the changes in gene sequences we will find out if this happened or not.'

The study was funded by the Human Frontier Science Program, NERC and BBSRC.