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Virginal shrimp not so chaste after all?

March 27, 2006 By Michael Hopkin This article courtesy of Nature News.

Microscopic creatures may have been having secret sex for millions of years.

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Imagine going more than 200 million years without sex. That's what zoologists thought had happened to a microscopic shrimp-like animal called Vestalenula. But now it seems that the crafty creatures might have been at it all along.

Of the many specimens of Vestalenula that have been examined over the years, all have been female. Researchers assumed that with no males in the picture, the creatures were reproducing solely asexually. Their supposed lack of a sex life even gave them their name, taken from the Vestal Virgins of Rome, a collective of chaste priestesses.

A bit like buses, three have come along at the same time.
David Horne
Queen Mary, University of London, UK
But now the story has changed, with the discovery of three live males, the first ever found. "Thousands of specimens have been studied in the past with no sign of a male," says David Horne of Queen Mary, University of London, UK, one of the zoologists unveiling the find. "Now, a bit like buses, three have come along at the same time."

An expedition led by Horne's colleague Robin Smith of Japan's Lake Biwa Museum discovered the three lucky males living among hundreds of females in a freshwater spring on the island of Yakushima. They report the discovery in Proceedings of the Royal Society B1.

The group of organisms represents a new species, which the researchers have christened Vestalenula cornelia, after Cornelia, a Vestal Virgin who was accused of taking an illicit lover. "It's a good name for something that was thought to be chaste but might have been having sex all along," says Horne.

It is unclear whether or not Vestalenula relies mainly on asexual reproduction with a periodic bout of sex thrown in for good measure, the researchers say. The three males found in Japan had no sperm in their bodies, but this might have been because they had used it all up.

Dry spell

The dubious honour for evolution's longest dry patch may now be passed to bdelloid rotifers, primitive animals that are thought to have reproduced asexually for the past 40 million years.

These creatures are unlikely to have been carrying out secret liaisons. In contrast to Vestalenula, for which zoologists based their no-sex theory simply on the lack of males in the fossil record, examination of rotifer DNA suggests that females always reproduce simply by cloning themselves.

That strategy is usually an evolutionary dead-end, says Horne. Without sex, which shuffles up genes and helps to shake out disadvantageous mutations, species eventually succumb to the gradual accumulation of genetic defects.

As for bdelloid rotifers, it remains a mystery how they have maintained their lonely existence for so long. Most asexual animals tend to go extinct after about a million years or so, says Horne. "But you get some species that appear not to have read the textbook."

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References

  1. Smith R. J., Kamiya T. & Horne D. J.Proc. R. Soc. B., doi:10.1098/rspb.2005.3452 (2006).

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