Evidence recovered from polluted DNA

CONTAMINATED crime-scene DNA samples that would normally be written off as forensically useless can now be rescued, thanks to amplification enzymes that tolerate pollution.

Before a profile can be obtained from a DNA sample recovered from a crime scene, it must be amplified using enzymes called polymerases. Pollutants such as tobacco or aluminium from drink cans can stop the enzyme working, but now Johannes Hedman and colleagues at the Swedish National Laboratory of Forensic Science have come up with some alternatives to the AmpliTaqGold enzyme, which is preferred by forensic labs.

The team amplified 32 polluted samples of saliva using three other polymerases regularly used to process non-forensic samples. Of these samples, 20 showed statistically significant improvements in the quality of the profile compared with using AmpliTaqGold (Biotechniques, vol 47, p 351).

Hedman suggests that employing these enzymes could be useful for samples that till now would not yield a complete DNA profile.

What drives a lion to think, ‘I feel like a human tonight’

WHEN the food gets scarce, it’s every lion for itself.

In 1898, according to numerous accounts and no fewer than three Hollywood movies, two male lions went on a 9-month killing spree around the Tsavo area of Kenya, devouring between 28 and 135 workers building the Kenya-Uganda railway.

Now an analysis of bone and hair samples from the notorious duo has backed the theory that scarcity drives dietary specialisation, and shows that food preferences can diverge

within co-operating groups . By comparing the isotopic

ratios of nitrogen and carbon in the lions’ remains with that of contemporary lions, humans and herbivore prey, Justin Yeakel of the University of California, Santa Cruz, estimates the lions ate around 35 people.

The study also made a surprise finding. “One lion was consuming a lot of humans, and one was not,” Yeakel says (Proceedings of the

National Academy of Sciences, DOI: 10.1073/pnas.0905309106). He attributes 24 deaths to one

SOME earthquakes can leave a legacy

of aftershocks that last for centuries.

Low-level seismic rumbles appear

to foreshadow many quakes. Yet not

always: the 2008 Sichuan quake in

China (pictured) came out of the blue.

These rumbles may not be precursors

but aftershocks – readjustments at

a fault following a larger event, in

some cases centuries earlier.

Seth Stein of Northwestern

University in Evanston, Illinois, and

colleagues analysed the rate of fault

slip in various tectonic settings. At

plate boundaries, motion rapidly

“reloads” a fault with new stress

and changes conditions there, so

tremors that can be clearly identified

as aftershocks typically end within

a decade, they found. Far away from

plate boundaries, however, fault

reloading is much slower, and

aftershocks can continue for

hundreds of years. The New Madrid

fault in Missouri, for instance, may

be experiencing aftershocks from

a quake in the early 1800s (Nature,

DOI: 10.1038/nature08502).

Seismic activity away from plate

boundaries “tells you more about

where large quakes were than where

the next one will be”, says Stein.

Quakes centuries apart may be linked

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cat, or 30 per cent of its diet, and 11 deaths to the other, just 13 per cent of its food.

By the late 19th century, elephants in the area had been hunted away, causing grasslands to become overgrown woodlands and the number of ungulate prey to decline.

Most lions probably left the region, but two turned man-eaters, Yeakel speculates. “People are a dangerous food to go after,” he says. “One lion was able to figure out how to do it and wasn’t afraid, the other was not.”

Caviar tag to save Caspian sturgeon

FARMED sturgeon on special diets

could undermine the market for

illegal caviar and help save the

species from extinction.

International regulations

introduced this year mean only

caviar from farmed sturgeon can be

traded legally. But as there is no way

to tell if caviar is farmed or “wild”,

the new rules offer scant hope for

sturgeon in the Caspian Sea, where

overfishing has reduced their

numbers by 90 per cent in the past

two decades. Until recently, the

Caspian supplied 90 per cent of the

world’s caviar.

Sven Wuertz at the University

of Kiel, Germany, and his colleagues

put capric acid, a fatty acid, in the

food of female sturgeon and found

that the tracer accumulated in their

eggs after 10 days. The amount of

capric acid in the resulting caviar

was too low to change its taste.

Wuertz believes his team has

hit on a cheap and simple tool to

“tag” farmed caviar. Once fully

tested, it could help the Convention

on International Trade in

Endangered Species, which

at present relies on labelling to

regulate where caviar comes from.

The study is important, says

Phaedra Doukakis, a caviar

conservation biologist at Stony

Brook University, New York, as

ways to distinguish wild and

aquacultured caviar are needed.

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24 | NewScientist | 7 November 2009