Worms contaminated by radioactivity from the Chernobyl nuclear accident have started having sex with each other instead of on their own.
According to Ukrainian scientists, they may have changed their sexual behaviour to increase their chances of survival. It is one of the first pieces of direct evidence on how wildlife is affected by radioactive pollution.
Although there is a wealth of evidence on the impact of ionising radiation on humans, its effects on wildlife are poorly understood. In the past the International Commission on Radiological Protection, which recommends radiation safety limits, has set no limits to protect wildlife, assuming that as long as humans were protected, animals and plants would be too.
But in recent years the ICRP has abandoned this assumption and launched an investigation into how best to safeguard “non-human species”. Many researchers are focusing on how wildlife has been affected by the radioactivity that spewed from the exploded reactor at Chernobyl in Ukraine in April 1986.
Gennady Polikarpov and Victoria Tsytsugina from the Institute of Biology of the Southern Seas in Sevastopol studied the reproduction of certain sedimentary worms that are vital to aquatic ecosystems. They compared the behaviour of three species in a lake near Chernobyl with the same species in a lake 20 kilometres away.
The lakes had similar temperatures and chemical composition, but the worms in the Chernobyl lake had received 20 times as much radiation as those in the other lake. The researchers found some remarkable changes in the worms’ sexual habits.
Two species had switched from asexual to sexual reproduction, as they are capable of doing. The proportion of Nais pardalis seeking partners for sex was five per cent in the normal lake but 22 per cent in the Chernobyl lake, while the proportions of Nais pseudobtusa doing the same were 10 per cent and 23 per cent respectively. However, the third species, Dero obtusa, showed double the rate of asexual reproduction in the polluted lake.
Polikarpov thinks the worms have switched to sexual reproduction in an attempt to protect themselves from the radiation. Sexual reproduction allows natural selection to promote genes that offer better protection from radiation damage, and “the resistance of populations as a whole will be increased”, he suggests.
Carmel Mothersill from the Dublin Institute of Technology, one of the experts helping the ICRP develop its new policy on protecting wildlife, agrees. “It is a plausible mechanism,” she says.
Journal reference: Journal of Environmental Radioactivity (vol 66, p 141)