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Fish take turns to solve problems

18 January 2010, by Sara Coelho

Unless you're a hermit living isolated from other people, you've probably realised by now that patience is a virtue and sometimes you just have to wait for your turn. Now scientists have found that sticklebacks have learnt this lesson as well.

Stickleback

This is the first time fish were observed 'taking turns to solve a common problem,' says Jennifer Harcourt from the University of Cambridge, lead author of the paper, which was published last week in Current Biology.

'It's very exciting to identify a new mechanism of conflict resolution in animal behaviour.'

Harcourt and colleagues were looking for the rules that individuals living in groups use to solve conflicts. To do that, they first had to create a problem.

Stickleback fish can be shy and they like to spend their time near the riverbed, sheltered from predators by weeds. When they do need to go out and eat in exposed areas, they look for safety in numbers: 'sticklebacks tend to synchronise their trips out of cover to look for food,' explains Harcourt.

The team trained individual stickleback fish to expect food at either the left or right end of the tank. After two or three days each stickleback knew exactly where to find its meal.

'We then paired fish with different set preferences in the same tank, separated by a transparent partition,' says Harcourt. This caused a problem for the sticklebacks: one wanted to leave the shelter to go left while the other was keener to go right. But neither fish wanted to leave the weeds and go foraging in an exposed area of the tank alone. So what to do?

Set up

Experimental setup (A.King)

The answer is very simple: 'they take turns,' says Harcourt, who recorded sticklebacks on tape and used statistical tools to make sense of their behaviour. The analysis revealed that the fish were willing to escort the other stickleback to its preferred side of the aquarium, even if there is no food waiting for them, and they expected the others to follow them in turn.

Taking turns means that both fish make trips in vain and leave the shelter without being rewarded with food, but the scheme works because it lowers the overall risk of being exposed to predators.

'The fish changed their behaviour in response to the other's movements,' says Harcourt. 'This is the first time we observe fish taking turns and sharing leadership to solve a conflict of interests.'


Harcourt et al., Pairs of Fish Resolve Conflicts over Coordinated Movement by Taking Turns, Current Biology (2009), doi:10.1016/j.cub.2009.11.045


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