The genetic basis of the switch from white to black in the peppered moth, a rare example of rapid evolutionary change, is no longer a grey area.
The peppered moth is famous in evolutionary biology for coming in two varieties - dark and pale - that each have a survival advantage under different circumstances.
Hundreds of years ago the white-coloured moths flourished, but during the industrial revolution their environment became blackened with soot. The dark–coloured moths quickly became the dominant form as they were less likely to be seen by predatory birds.
Dr Ilik Saccheri from Liverpool University, an author of the study, explained that it was about time the peppered moth’s genome was investigated.
“No one had previously attempted to actually identify the underlying genetic mechanism.”
His group used a technique called genetic linkage to find the area of the moth's genome where the colour switch gene must be.
This involves looking at 'markers', short DNA sequences with known locations, that are randomly distributed along the moth’s genome. They found a marker that is inherited together with the dark colour. This means that it is likely to be in the same region as the colouring gene, as genes that are close together are less likely to be broken apart and inherited independently during sexual reproduction.
“We were able to identify not the causal mutation itself, but a narrowly defined region on a particular chromosome within which the causal mutation must reside” Saccheri explained.
But there is no known protein that could cause colour change contained within this region of the moth's genome. Instead, the authors speculate that the area codes for a regulatory molecule, which in turn controls colour.
“The same region has been found in Heliconius butterflies controlling wing patterning ... the interesting thing is that these two species are very, very distantly related. It’s intriguing that we should find them in the same location.”
The fact that this genomic region is responsible for colour patterning in two different organisms suggests that there is an important gene that has been protected from the abrasive effects of evolution.
“We wanted to update this classic textbook example of adaptation that is currently lacking a molecular dimension – it is stuck in the 70s and 80s. By doing that we are adding another layer of evidence to demonstrate that this phenotype was subject to very strong and recent selection.”
Irik Saccheri explains the discovery of the genetic region underpinning the rapid evolution of the peppered month.