Extreme evolution to avoid extinction

This story about butterflies in Samoa is an example of the fastest natural selection observed so far, and shows that evolution can accelerate when a major threat arises.

At the risk of extinction, butterflies on two islands in the South Pacific quickly developed a gene defense barrier to help them cope with the situation.

In 2001, the male butterflies of Hypolimnas bolina on Savaii and Upolu Island (Samoa Islands) were extremely rare. They only account for 1% in their populations. The cause of this condition is that they are attacked by Wolbachia - a parasite transmitted through females that kills male butterflies before they hatch.

Last year, the number of males was close to that of females. This is because they have developed a gene mutation that allows the bacteria to be destroyed, energized by the guys and allowed them to multiply rapidly.

"This is one of the clearest and fastest examples of evolution under natural selection pressure," said Sylvain Charlat of the University of London, the study's author.

The male butterfly of the Hypolimnas bolina (Photo: Sylvain Charlat / Science)

To check whether the boys' resurgence was due to genetic changes in themselves or parasites, the team mated parasitic infected butterflies with male butterflies from an island. The other does not have this gene mutation.

Later, the offspring of the couple were mated to butterflies on an uninfected island, to dilute the gene that could kill the parasite."After doing that for 3 generations, we received a population where all the males were killed," the team said.

This proves that the mutated gene is formed within the male butterflies in danger.

T. An