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A male Eggfly or Blue Moon Butterfly, Hypolimnas bolina Photo credit: Sylvain Charlat/Science |
This example of evolution from 2007, the evolution of the Blue Moon butterfly on the South Pacific Samoan islands of Upolu and Savaii, is one of the fastest on record other than the rare occasions of a stable hybrid giving rise to a new species.
It appears to have happened in just a few years, over some ten generations, in response to intense selection pressure from a killer bacterium.
In 2001, researcher found that in the Samoan Islands, in populations of this butterfly, only about 1% were males. This was caused by a bacteria of the, Wolbachia genus, which infects females and which causes male embryos to die before hatching. The resulting success rate for egg hatching was also low.