A LOW dose of radiation makes earthworms switch from asexual to sexual reproduction.
Enchytraeus japonensis, a species of earthworm found in Japan, normally reproduces by breaking into six or more sections, each of which grows into a new worm. But when Yukihisa Miyachi and colleagues from the International University of Health and Welfare in Otawara, Japan, exposed the worms to 4.5 micrograys of radiation per hour, about 15 times higher than natural background radiation levels, they stopped fragmenting. Instead, the researchers discovered that 85 per cent of the worms had produced eggs, some of which developed into juveniles, suggesting that the creatures had been having sex (Journal of Environmental Radioactivity, vol 79, p 1). The effect disappeared when the radiation level was increased to 30 micrograys per hour.
Keith Baverstock, a radiation scientist from the University of Kuopio, Finland, says that these changes could be 鈥渁 relic of evolutionary history鈥�. Radiation levels on Earth when worms evolved hundreds of millions of years ago were around 10 times higher than today.
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