BioEd Online

Global warming is influencing the genetics of fruitfly populations, according to a study carried out in Australia. Warming over the past two decades has encouraged genes to spread from insects at tropical latitudes into flies in more temperate areas.

The research adds to a growing body of evidence showing that living things, from insects to plants and other animals, are responding to the planet's shifting climate. A second study this week emphasizes that the warming is unlikely to end soon, thanks to a steady heating of the world's oceans that will keep air temperatures on the rise long after the release of greenhouse gases is curbed.

Researchers studying Australia's fruitflies (Drosophila) sampled the insects along the country's east coast and looked at a gene, called Adh, that is known to vary with latitude. Flies in the tropical north are more likely than their southern counterparts to carry a version called AdhS.

But that picture has been altered by rising temperatures, report Ary Hoffman, of La Trobe University in Bundoora, Australia, and colleagues. Hoffman's team sampled the flies in 2002 and 2004, and found that the distribution of AdhS had shifted some 400 kilometres south from where it was two decades earlier. They report the results in Science¹.

"We were surprised at the speed of the change. Twenty years is not long on an evolutionary time scale," Hoffman says. "In fact, we didn't believe the 2002 data at first, but then we found that flies collected in 2004 showed exactly the same pattern." The team also found a variant in another gene that had shifted 800 kilometres down the Australian coast.

Hotter and drier

The Adh gene produces an enzyme called alcohol dehydrogenase. This enzyme helps the human system to deal with alcohol consumption, although its purpose is different in the fly, where the 'S' version seems to encourage survival in hot, dry conditions.

Hoffman's team says the geographical shift of AdhS is probably due to climate change. Temperatures along Australia's east coast are rising by around 0.2 ºC every ten years, and annual rainfall is decreasing by 10-70 millimetres per year.

The discovery shows the power of latitude-linked genes to reveal the effects of climate change on living populations. "There is now much more information on these patterns in genetic markers, which will form a rich source for future studies," says Hoffman.

Warmth warning

In the same issue of Science, climate modellers report that they have calculated how much the Earth is being warmed. According to their analysis of the amount of heat stored in the oceans, every square metre of the planet is receiving net power of 1 watt from the Sun, after subtracting energy that is radiated out into space².

This provides yet more evidence that Earth is being slowly but surely heated, says the team, led by Jim Hansen of NASA's Goddard Institute for Space Studies in New York. "This energy imbalance is the smoking gun that we have been looking for," he says.

Given all the energy currently stored in the world's oceans, further global warming could only be stopped immediately by halving the amount of carbon dioxide in the atmosphere, Hansen claims. "But that is not practicable in the foreseeable future, so the world is going to become warmer," he says.