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Hawaii cricket world's fastest-evolving invertebrate: US biologists
www.chinaview.cn 2005-02-06 10:15:49

    LOS ANGELES, Feb. 5 (Xinhuanet) -- Laupala cricket, a cricket living in Hawaii's forests, may be the world's fastest-evolving invertebrate, US biologists said Saturday.

    Finicky mating behavior appears to be the driving force behind the speedy speciation of the cricket, scientists at Lehigh University and the University of Maryland wrote in the Nature journal, saying the findings shed light on the role of individual choices in the evolution of species and the growth of biodiversity.

    Females in the Laupala genus detect tiny differences in the pulse rates of male courtship songs, which differ from one speciesto the next. They refuse to mate with males of other species, thuspromoting the formation of new species.

    "Animals with nerve systems and brains have preferences and canmake choices," said Tamra Mendelson, evolutionary biologist at Lehigh University. "Changes in these preferences and choices appear to drive speciation."

    "What turns a female cricket on? Why does she prefer one pulse rate over another? Whatever the reason, it's very important that she exercise this preference in order to keep the species distinct."

    The thumbnail-sized Laupala spawns new species at the rate of 4.17 every 1 million years, more than 10 times faster than the average speciation rate for invertebrates.

    This rapid evolution is contributing to an "explosion" of new cricket species, especially on Hawaii, the largest and youngest island in the Hawaiian archipelago, scientists wrote in their paper.

    Some 38 different species of the cricket now inhabit the islandchain. Among all animals, only the African cichlid fish spawns newspecies more quickly, but the fish is a vertebrate.

    While early biologists based their estimates of speciation rates on structural characteristic, scientists today are more likely to use genetic data to come up with estimates, Mendelson said.

    Closely related species of Laupala have no clear morphological differences. They are similar in appearance, have similar diets, and live in similar habitats. There are no physiological differences that would prevent them from interbreeding.

    But they are distinguished by subtle differences in the pulse rates of male crickets' simple courtship songs, a secondary sexualtrait that plays a large role in mate attraction.

    Among all species of Laupala, pulse rates of male courtship songs range from 0.5 to 4.2 pulses per second. Female crickets candetect these differences, and they tend to hop towards the pulse rate of their own species and to reject songs sung at a different tempo.

    As a species begins to split into two separate species, the songs appear to be the first characteristic that changes, according to Mendelson.

    During the early part of the speciation process, crickets of the two emerging lines interbreed. After a point, however, membersof the two distinct species no longer mate with each other.

    "Over time, lineages, species that have split, cease to recognize each other as mates, although the ancestors did. In the case of Laupala, members of the two species are physiologically capable of mating, but they appear to lose the desire to interbreed," Mendelson said in the paper. Enditem

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