SSS 2009-11-09（在线收听）

Evolution continues today, and sometimes we can watch it happening. Researchers in the November 6th edition of the journal Science say that they caught in the act a population of butterflies in Ecuador potentially diverging into two distinct species.

Heliconius butterflies spread across Central and South America. What distinguishes differing Heliconius species is color variation. For instance, in Costa Rica, the two most closely related species are white or yellow, which prefer to mate with those of their own color.

In Ecuador, there are also white or yellow Heliconius butterflies that live close to one another and have mated freely. But that situation might be changing. Scientists studied the butterflies in captivity. The two types differ in just one gene responsible for color. But yellow males prefer yellow females. While white males go for either color female.

The difference in mate preference could eventually lead to two distinct species, as in Costa Rica, with yellow and white butterflies that no longer interbreed. The researchers will continue to study the role of genes in both color and mate choice—which could send the populations diverging forever into new species.