A transposon underlies this classic story of evolutionary adaptation.
Scientists have finally identified the genetic change that enabled the black peppered moth (Biston betularia) to change shades—from a light, speckled color to a dark brown hue—to camouflage itself against Britain’s soot-blackened trees during the Industrial Revolution: a mutation in a gene calledcortex, according to a study published last week (June 1) in Nature. The same gene was found to control color in butterflies, according to another study published at the same time in the same journal.
In the former study, Ilik Saccheri of the University of Liverpool, U.K., and colleagues crossed light- and dark-color moths and mapped their genetic differences. From a genetic sequence of 400,000 bases, the researchers homed in on 87 differences, which they tested individually. The team finally traced the color change to a transposon or “jumping gene” located in the cortex gene.
“It’s this huge chunk of DNA that doesn’t itself code for anything, but somehow disrupts the nature of the gene,” Saccheri told The New York Times.
By examining the genetic variance around this mutation, Saccheri’s team estimated that the hue-altering mutation occurred within a 10-year period around 1819, which fits with records of the black moths’ first sighting in 1848, according to BBC News.
“This is an incredible piece of work,” James Mallet, an evolutionary biologist at Harvard University and University College London who was not involved in the study, told the BBC. “These have been incredibly difficult animals to work with,” Mallet said, “So it’s very hard to use standard genetic techniques to map the genes and locate them on the chromosomes.”
In the latter study, Nicola Nadeau from the University of Sheffield, U.K., and colleagues found that the same gene controls color in butterflies of the Heliconius family. But instead of using it to camouflage themselves, the butterflies use their bright coloring to warn off predators by mimicking the coloration of toxic butterfly species.
Taken together, the findings suggest that the cortex gene is an important target of natural selection for coloration and patterning in these winged insects, Nadeau and colleagues reported in their study.