Unique island love song attracts flies.

Unique island love songs attract flies

While most of us visit the Hawaiian islands for surf and sun, a few are drawn by flies and their tropical romances. These researchers want to hear not the love songs of beach-side steel guitars, but the clicks, purrs and hums of insect courtship in the mountains. Some species of Drosophila flies unique to the islands, say the scientists, have developed mating songs radically different from those of related stateside songsters. By studying the sounds, the researchers hope to decipher the evolutionary relationships between the Hawaiian flies and their continental cousins.

Stalking Drosophila at 6,000 feet above sea level, Ronald R. Hoy of Cornell University in Ithaca, N.Y., and his colleagues captured on tape some unexpected communiques from 20 of the 106 species of Hawaiian picture-winged Drosophila. Hoy, Anneli Hoikkala of the University of Oulu in Finland and Kenneth Kaneshiro of the University of Hawaii in Honolulu report in the April 8 SCIENCE that the island songs differ from continental songs in either how they sound or how they are produced.

For example, Maui's D. fasciculisetae makes what the scientist call a click-song, described by Hoy as the sound of running a thumbnail across a plastic comb. He said in an interview that these high-frequency clicks have not been reported among continental Drosophila or any other flies. Hoy and his co-authors group the island sounds into four song types; the click-song, a complex pattern of short pulses followed by a trill of sound, a purr made of steady sound pulses and a low hum. Some flies use their wings to create their music; others vibrate their abdomens.

The scientists have yet to prove these sounds are true courtship songs, or that they actually are heard by other flies, says Hoy. But based on Drosophila behavior elsewhere, he adds, it would be "astounding" if the flies did not use the sounds for mating rituals. Before recording, the scientists kept the sexes separate for two weeks "to build up motivational levels," says Hoy. Some of the romantic overtures noted are rather elaborate for a fly: The male of Hawaii's D. silvestris purrs while close in front of the female, then stands behind her with his head under her wing and hums -- "until the female accepts him or decamps." Other species use similar body language, suggesting the flies feel the vibrations of sound rather than hear them, says Hoy.

Despite its modus operandi, says Hoy, D. silvestris is one of the more primitive island Drosophila. He explains the researchers are trying to build "an acoustical phylogeny" of the flies based on sound analyses. In other words, they are matching the song style of a species with its place in evolution.

These Drosophila are not the drab D. melanogaster all too familiar to genetics students. Instead, says Hoy, the larger Hawaiian cousins are more flamboyant in both appearance and communication skills. Some biologists estimate that more than 500 different Drosophila species have evolved on the islands, producing flies not found anywhere else on earth. Hoy says that number may actually be greater than 700 species, with the "younger" flies evolving within the past 400,000 years and others dating back at least 5 million years. "[When they evolved] is a point under contention by biologists," says Hoy. "Some think there have been flies on the Hawaiian islands for 20 million years."

"The only way to make it [to Hawaii] was to have your ancestors blown in and then speciate from there," Hoy says. But it is uncertain whether there was one mother fly from the mainland whose offspring then "island hopped" to start new colonies, or whether an occasional new "founder fly" crossed the ocean and populated the various islands separately. Evidence supports the one-original-fly idea, says Hoy, who adds that "however it happened, it is certainly the case that these Drosophila evolved from mainland species."