Sky

From physorg.com.

A male-killing bacteria has led to skewed sex ratios in populations of Hypolimnas bolina butterflies in the South Pacific, but researchers have found that male butterflies on some islands have bounced back thanks to the rise of a suppressor gene.

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.

This study shows that when a population experiences very intense selective pressures, such as an extremely skewed sex ratio, evolution can happen very fast.

It is not yet clear whether the suppressor gene emerged from a chance mutation from within the local population, or if it was introduced by migratory Southeast Asian butterflies in which the mutation had already been established.

The suppressor gene allows infected females to produce males, these males will mate with many, many females, and the suppressor gene will therefore be in more and more individuals over generations.

“We usually think of natural selection as acting slowly, over hundreds or thousands of years,” said Hurst. “But the example in this study happened in a blink of the eye, in terms of evolutionary time, and is a remarkable thing to get to observe.”

“In essence, organisms must evolve or change to stay in the same place, whether it’s a predator-prey relationship, or a parasite-host interaction,” said Charlat. “In the case of H. bolina, 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.”