Posted on: Friday, February 11, 2005

Hawaiian lady crickets very picky

By Jan TenBruggencate
Advertiser Science Writer

Hawaiian crickets on the Big Island evolve into new species faster than any known invertebrate, and they do it based on the pace of courtship chirping, scientists have found.

Biologists writing in the Jan. 27 issue of Nature magazine said female crickets in the Laupala genus detect minute differences in the chirping of males, and base their choice of mates on it. Laupala crickets are known as "rusty day-singing crickets," and their songs have been compared to the sound of sleigh bells, said Lehigh University researcher Tamra Mendelson.

The key factor in chirps appears to be the rate of the beat, she said. The crickets have chirp pulse rates ranging from 0.4 per second to 4.4 per second, differing among species.

Even though the females may be capable of successfully reproducing with other males, they refuse to mate with males who don't match their chirping preferences.

Initially, the difference in their chirps is the only difference between the crickets. But eventually, as crickets with one song breed exclusively with each other, they evolve into new forms, and fidelity to the song keeps the species distinct, Mendelson said.

She and University of Maryland evolutionary biologist Kerry Shaw concluded that Laupala crickets evolve a new species 4.17 times in 1 million years. They say that's an explosive pace, more than 10 times the rate at which other invertebrates do so.

Mendelson said that Laupala crickets are found on all the main Hawaiian islands, but that the species evolution rate is highest on the Big Island. There are now 38 species of Laupala crickets in the Islands.

Why is this happening in Hawai'i?

"It is almost certainly a function of volcanic islands, geographic isolation and the rapid evolution of mate recognition behavior," Mendelson said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.