UCL in the News: Butterfly shows evolution at work

The tropical blue moon butterfly has developed a way of fighting back against parasitic bacteria.

Six years ago, males accounted for just 1% of the blue moon population on two islands in the South Pacific.

But by last year, the butterflies had evolved a gene to keep the bacteria in check and male numbers were up to about 40% of the population.

Scientists believe the comeback is due to "suppressor" genes that control the Wolbachia bacteria that is passed down from the mother and kills the male embryos before they hatch.

"To my knowledge, this is the fastest evolutionary change that has ever been observed," said Dr Sylvain Charlat [UCL Biology], whose study appears in the journal Science. …

The researchers are not sure whether the gene that suppressed the parasite emerged from a mutation in the local population or whether it was introduced by migratory Southeast Asian butterflies in which the mutation already existed.

But they said that the repopulation of male butterflies illustrates rapid natural selection, a process in which traits that help a species survive become more prominent in a population.

"We're witnessing an evolutionary arms race between the parasite and the host. This strengthens the view that parasites can be major drivers in evolution," Dr Charlat said.

BBC News