10 April 2010 | NewScientist | 15

A little stress may boost fetal brain

HIGH stress during pregnancy is bad news, but it turns out that moderate stress might boost fetal brain development.

Studies in rodents suggest that stress during pregnancy inhibits neural growth, while the children of women who lived in war zones during pregnancy have a higher risk of developing schizophrenia.

To investigate the effects of moderate stress in humans, Janet DiPietro and her colleagues at Johns Hopkins University in Baltimore, Maryland, examined 112 healthy pregnant women living in the US three times during their third trimester. They asked the women about their stress levels and recorded fetal movements. They also examined the babies two weeks after birth.

Women who reported higher stress levels during pregnancy had babies that moved around more in the womb. After birth, these babies scored higher on a brain maturation test, although they were more irritable. More active fetuses had better control of body movements after birth.

The stress hormone cortisol plays a role in brain maturation, which may help explain the result (Child Development, vol 81, p 115).

Justice for all – if I get a grape, so should my partnerCHIMPS recognise unfairness, even when it involves individuals other than themselves. This sense of unfairness towards others may be a rudimentary form of the social justice that characterises human societies.

In earlier studies several apes, monkeys and even dogs responded negatively when they received a meagre reward for the same task that earned others a more lavish pay-off. But none of these animals apparently recognised unfairness directed at others.

Sarah Brosnan, a primate

behaviourist at Georgia State University in Atlanta, and her colleagues trained captive chimps to exchange tokens for a food reward, then tested how same-sex pairs of chimps reacted to various levels of reward. As expected, chimps were more likely to reject a boring carrot when their partner got a yummy grape for the same token. Surprisingly, the chimps were also more likely to reject a grape if their partner only got a carrot (Animal Behaviour, DOI: 10.1016/j.anbehav.2010.02.019).

In previous experiments,

SOME lizards escape predators by shedding their tail, but the experience appears to leave its mark. After losing their tail, lizards end up with damaging changes to their DNA.

The parts affected are the telomeres – stretches of DNA that cap the ends of chromosomes. Telomeres naturally shorten as cells divide, and shortened telomeres are associated in humans with the effects of ageing.

The shortened telomeres found in lizards that had lost their tail in a brush with a predator add to the evidence that environmental stress produces negative effects by eroding telomeres.

The changes were observed by Mats Olsson of the University of Wollongong in New South Wales, Australia, and colleagues when they measured the telomeres of wild sand lizards, Lacerta agilis (Biology Letters, DOI: 10.1098/rsbl.2010.0126).

The team found that telomere length was especially affected in larger males, compared with females or smaller males. Olsson suggests that this is because larger males live more stressful lives than other lizards: they engage in more contests for female partners and are more likely to be attacked by predators.

Brush with death leaves mark on DNA

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other groups of chimps showed no sensitivity towards unfairness directed at others. Perhaps Brosnan’s animals rejected their “undeserved” grapes in part because they sat right next to their less fortunate partner and may have feared retaliation for their windfall, the researchers suggest.

But the chimps’ awareness of the mistreatment of others as well as themselves also lays the groundwork for complex social interactions more like those of human groups, they note.

Fiddler crabs love their neighbours

AFRICAN fiddler crabs will put their claws on the line to help defend their neighbours from an intruder – but only because it suits them.

Defence coalitions ought to be common in the wild, says Michael Jennions of the Australian National University in Canberra, but in practice they have only been seen in two fiddler crab species, and European rock pipits.

Jennions and colleagues tethered “intruder” crabs next to the burrows of two established crabs, then released them. The neighbouring crabs formed alliances that significantly increased their chances of repelling the intruder. Alliances were strategic. In most cases, crabs with burrows would only assist their neighbour if they were bigger than both the intruder and the neighbour, and had a good chance of winning.

“The best explanation is better the devil you know,” he says. “By retaining a familiar neighbour you don’t have to re-negotiate territorial boundaries.” Crabs with unfamiliar neighbours had more border disputes than those that knew their neighbours, and when attacked by intruders, were less likely to form territorial coalitions. “If you lose your neighbour it is likely to be to a larger neighbour, that is going to need more territory,” says Jennions. Plus, larger fiddler crabs get the females, he adds.

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