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Taking courage. In pairs of three-spined sticklebacks, a faithful follower can prompt boldness from the leader.

Hey, Fish, Got My Back?

Inspirational followers may be just as important as stellar leaders, at least in fish. A new study finds that timid three-spined sticklebacks can inspire greater daring in their bold counterparts. The findings illustrate that leadership may be as much a product of social context as of individual temperament.

Over the past several years, researchers have worked to understand how complex group behaviors arise from simple decisions by individuals. For instance, an ant trail might form on one tree branch instead of another because the first few ants randomly picked that branch and later ants followed their scent. But according to evolutionary biologist Andrea Manica and her colleagues at the University of Cambridge in the United Kingdom, much of the work has focused on situations in which all individuals are genetically very similar, such as groups of social insects. Less well understood, says Manica, is how the greater, individual differences in vertebrates' personalities can influence group behavior. In these situations, certain individuals often become group leaders.

Previous studies have identified boldness--the amount of time an individual is willing to stay exposed in order to forage for food--as a trait of leaders in groups of sticklebacks (Gasterosteus aculeatus). To understand how boldness could translate into leadership, the Cambridge team set up aquaria in which one side was a "safe area" with deep water and plastic plants and the other side was a "risky," exposed area designed to make the fish feel vulnerable to being eaten by birds. The team placed one stickleback in each aquarium half, separated them with an opaque divider, and trained the fish to expect food only in the exposed area: To eat, the fish had to take risks. The scientists then observed each fish's behavior and assigned it a score on a boldness scale. They then randomly repaired the fish, using the boldness scores to classify each fish as either "bold" or "shy," relative to its new partner. This time they inserted clear and opaque dividers into the tanks.

In a paper published online today in Current Biology, the team reports that when the fish could see each other, the shier fish took their cue from the bold ones, following them out of cover. The shy fish spent more than twice as much time exposed when they could see their bolder companions than when they couldn't. That part, says Manica, was expected. But something else occurred. In the presence of their shy followers, the bold fish also upped the amount of time they spent out of cover by an average of nearly 10%. According to Manica, it appears that the bolder fish were responding to social feedback. "Having a really faithful follower was making the leader more prone to initiate trips into the ... risky areas," says Manica. The next step, she says, will be seeing how followers affect leaders in larger groups of sticklebacks.

The new findings are important because they "[raise] the possibility that leadership may not be fixed" in an individual, says Stephan Reebs, an ethologist at the Université de Moncton in Canada. Instead, "[it may] increase as it gets reinforced by contact with willing followers." But Odile Petit, a primate ethologist at the Institut Pluridisciplinaire Hubert Curien in Strasbourg, France, would like to have seen more evidence that the increased time leaders spent exposed when in the presence of a shy fish is truly because they had a faithful buddy rather than some unknown variable that the experiment didn't test.

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