Butterfly mating to split species

A population of tropical butterflies could be evolving into two separate species, scientists believe.

The Heliconius butterflies in Ecuador have either white or yellow wings as determined by a single gene.

Scientists who studied the insects in captivity found yellow males prefer a mate of their own colour, while white males are not so picky.

The behaviour could be the start of a process splitting one species into two through reproductive isolation, the researchers believe.

This already appears to have happened to another population of Heliconius butterflies in Costa Rica.

Here, there are two closely related but separate species with white and yellow wings.

Both strongly prefer to mate with butterflies having the same wing colour as themselves. The research is reported in the journal Science.

Study leader Dr Marcus Kronforst, from Harvard University in Boston, said: "The subtle difference in mate preference between the colour forms in Ecuador may be the first step in a process that could eventually result in two species, as we see in Costa Rica."