Hormone makes meerkats more cooperative

Dosing meerkats with the hormone oxytocin makes them spend more time and energy helping others in their group, according to a new study.

And it doesn’t just affect one or two of meerkats’ wide range of cooperative or ‘pro-social’ behaviours – it boosts a broad spectrum.

This finding may hold the answer to why social animals don’t just help out with tasks they will directly benefit from, like digging burrows – they also do things for the good of the group that actually cost them as individuals, like giving food they’ve caught to other group members’ young.

‘All the co-operative behaviours seem to be controlled at a high level by the same pathway,’ says Dr Joah Madden of the University of Exeter, lead author of the paper, published in Proceedings of the Royal Society B. ‘One of the big questions in animal behaviour has been why individuals behave cooperatively. Until now, studies have typically looked at just one behaviour and tried to find explanations for it in isolation, rather than looking at altruistic behaviour as a whole syndrome.’

Madden and co-author Professor Tim Clutton-Brock of the University of Cambridge gave intramuscular injections of either oxytocin or a control saline solution to 36 wild meerkats from four groups living in South Africa’s Kuruman River Reserve. They then counted how often they behaved cooperatively over the next half hour.

Animals that had been given oxytocin showed significantly higher levels of cooperative behaviours – like helping dig burrows, guarding the group from predators and caring for young – than when they had received a placebo.

The effects on all the cooperative actions were noticeable. Individuals exposed to oxytocin showed around a 50 per cent increase in the amount of their food they gave to young. And they were about half as likely to behave aggressively.

Digging or guarding benefits all the animals in a group, but giving away food to pups may reduce the individual’s own nutritional state, while providing the feeder with limited direct benefits.

On the face of it, it’s easier to understand why animals would engage in the first kind of altruistic activity than the second. But this study suggests there’s a single mechanism controlling both kinds of altruistic behaviour. Because there is a whole suite of these cooperative activities, all moderated by a pathway involving oxytocin, the meerkats can’t selectively engage in one or two of them but ignore others.

‘Individuals could be caught in a bind in which they behave in ways that are harmful to them because these behaviours are part of the same system as other behaviours that are beneficial,’ Madden suggests. ‘Of course you would expect altruistic behaviour to be beneficial, or the animals wouldn’t do it,’ he adds. If the net result is generally beneficial, individuals might find themselves behaving in ways that harm their own interests.

‘Over time you would expect that natural selection will weed out specific behaviours that are costly for the individual and decouple them from those behaviours that provide benefits, but this can take a long time,’ Madden adds.

Oxytocin acts as a neurotransmitter in mammals’ brains, and is released in largest quantities during childbirth. It’s already been shown to cause altruistic behaviour in voles, and studies have even shown that it can increase pro-social traits like trust and reliability in humans.

Madden says it would now be interesting to investigate the effects of oxytocin in a wider range of species, including both social and non-cooperative animals.

The research was funded directly by a grant from the Biotechnology and Biological Sciences Research Council, but built on work supported by earlier funding from the Natural Environment Research Council. A vet was present throughout the experiments to make sure the meerkats weren’t harmed.

Tom Marshall

http://planetearth.nerc.ac.uk/news/story.aspx?id=889

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