26 September 2009 | NewScientist | 17

A KILLER fungus may break the chemical stalemate that is hampering anti-malaria efforts.

Mosquitoes that carry malaria are becoming increasingly resistant to insecticides . In theory, spraying two different types of insecticide at once postpones resistance, as bugs that resist one type are killed by the other. This strategy doesn’t work as the enzymes mosquitoes use to

disable one class of chemicals tend to cripple other classes too.

Entomologist Bart Knols and colleagues at Wageningen University in the Netherlands wondered if the same problem would mean insecticide-resistant mosquitoes would be able to fend off a fungus. This was not the case: the fungus killed mosquitoes resistant to the three classes of chemicals commonly used in

Mutant mice live the dieter’s dream

IT’S a dieter’s dilemma: reducing the number of calories consumed can cause your metabolism to slow, making it harder to fight the flab.

Now Leona Plum of the Naomi Berrie Diabetes Center at Columbia University Medical Center in New York and colleagues have overcome this problem in mice.

The team genetically engineered mice to lack a protein that directly controls the gene Cpe, which is known to make mice susceptible to obesity . This caused the mice to eat less than controls, while their metabolism remained high. After six weeks they weighed 15 per cent less (Nature Medicine, DOI: 10.1038/nm.2026).

Plum claims it is the first time a team has managed to dissociate food intake from energy expenditure. If drugs could target the corresponding gene in people, it might allow dieters to keep burning calories at the same rate they do when eating normally.

Years of separation belie Indians’ shared ancestry

THE Rigveda, a collection of Sanskrit hymns written

around 3500 years ago, doesn’t contain much genetics.

It does, however, have the first mention of India’s caste

system, and now a genetics study reveals that inbreeding

going back thousands of years has led to marked genetic

differences between castes. It also shows that India’s many

distinct peoples spring from just two ancient populations.

Nick Patterson of the Broad Institute in Cambridge,

Massachusetts, and colleagues examined fragments of

DNA from 25 groups across India. They included castes

and hunter-gatherer tribes, or “scheduled populations”.

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Fungus kills resistant mosquitoes Africa (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0908530106).

“As a bonus,” Knols says, “fungal infection makes insects that resist pyrethroids susceptible again.” Fungal infection might weaken the insect and its resistance mechanisms. In addition, a smaller dose of chemicals will kill fungi-infected mosquitoes, good news as one of the chemicals is DDT which persists in the environment.

Each of these groups was genetically distinct, but the

profiling indicated that all Indians spring from one of two

populations: Ancestral North Indians (ANI), who are

genetically close to Europeans, and Ancestral South

Indians, who are distinct from both east Asians and ANI

(Nature, DOI: 10.1038/nature08365).

“If you’re trying to understand disease and distribution

between south and north India, there could be

environmental or lifestyle issues,” says Patterson, “but

genetics could also offer a perfectly possible explanation.”

The analysis showed that castes are descended from a

small pool of ancestors and that an initial lack of genetic

variability has been reinforced by marriages within the

group. The current caste system has resulted in limited

gene flow for thousands of years, says Patterson.

A RARE meteorite that may hold clues to the early Earth has been discovered.

The basaltic meteorite, named Bunburra Rockhole, was found after it was spotted entering our atmosphere by the Desert Fireball Network in Australia, an array of cameras searching for meteors .

The uneven distribution of material in the meteorite and calculations of its orbital trajectory suggest it came from an asteroid a few tens of kilometres wide. This is unusual, as most basaltic meteorites come from a larger asteroid called Vesta. The parent asteroid may have been born close to the young sun, which hints that it is made of the same stuff that coalesced to form Earth (Science, DOI: 10.1126/science.1174787).

Clues to Earth’s origins fall from sky