Magazine article Science News

Mixed Butterflies: Tropical Species Joins Ranks of Rare Hybrids

Magazine article Science News

Mixed Butterflies: Tropical Species Joins Ranks of Rare Hybrids

Article excerpt

A South American butterfly has a checkered past, say biologists. It's one of the few animal species that seems to have arisen via a supposedly rare path: crossing two older species.

A black butterfly flashing bold stripes, Heliconius heurippa, came from the natural mixing of two other Heliconius species, says Jesus Mavarez of the Smithsonian Tropical Research Institute in Panama.

New experiments with H. heurippa suggest an answer to the difficult question of what keeps the hybrid species from blending back into its parent species. The hybrid's preference for mates of the same stripes keeps its species distinct, Mavarez and his colleagues say in the June 15 Nature.

"In animals, the dogma has been hybridization is a dead end--it's not important for creating species," comments Bruce McPheron of Pennsylvania State University in University Park, who's studied how some flies form species. The butterfly findings suggest that hybridization "can be a much more important source of new species than people have recognized," he says.

Botanists have long noted that many plant species arise from interbreeding, particularly when the hybrids end up with more chromosomes than the parent species. Altered chromosome number in hybrids has seldom been observed among animals.

Biologists are particularly interested in examples of new species in which the chromosome number remains constant. Mavarez and his colleagues focused on H. heurippa as a suspected hybrid butterfly species that has the same chromosome number as its two suspected parent species. …

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