An international team of researchers has documented a remarkable example of natural selection in a tropical butterfly species that fought back - genetically speaking - against a highly invasive, male-killing bacteria.
Within 10 generations that spanned less than a year, the proportion of males of the Hypolimnas bolina butterfly on the South Pacific island of Savaii jumped from a meager 1 percent of the population to about 39 percent. The researchers considered this a stunning comeback and credited it to the rise of a suppressor gene that holds in check the Wolbachia bacteria, which is passed down from the mother and selectively kills males before they have a chance to hatch.
"To my knowledge, this is the fastest evolutionary change that has ever been observed," said Sylvain Charlat, lead author of the study and a post-doctoral researcher with joint appointments at the University of California, Berkeley, and University College London. "This study shows that when a population experiences very intense selective pressures, such as an extremely skewed sex ratio, evolution can happen very fast."
