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Planet Earth

The Wisdom of Crowds... of Stickleback Fish

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It's not just we humans who value consensus: A new study has shown that stickleback fish make better decisions when acting as a group than they do as individuals. Researchers set up a clever experiment in which the fish had to choose which leader to follow in the quest for food, giving them an option between a "good" choice and a "bad" choice.

Based on earlier experiments, the study’s researchers had a pretty good idea about ... stickleback preferences. Fat, evenly colored fish are regarded as healthy and strong, while scrawny fish mottled with black spots may be considered diseased. Coauthor Ashley Ward ... says of these sticklebacks, “Fish like large leaders, well-fed leaders and unparasitized leaders” [Science News]

. Researchers made a stickleback replica that looked healthy and fat as well as one that appeared bony and mottled, and put both into the fish tank.

When shown the fish replicas, the other sticklebacks in the tank would approach and follow one of the two replicas, which were moved around by remote control. Following a certain fish would be their version of casting a ballot.... When just one fish chose its leader, the fish would make the right choice, picking the healthiest leader about 55 percent of the time. That number went up to 80 percent with the eight-fish electorate [LiveScience].

The school of fish arrived at the "correct" answer through a beneficial feedback mechanism, researchers explain in an article in Current Biology [subscription required]. A few fish might catch sight of a potential leader's unsightly blotches that most of the fish hadn't noticed, and would strike out to follow the other leader. This behavior is in line with what study coauthor David Sumpter calls the quorum-response rule.

In this model, a few individuals are able to discern a difference between the two candidates and so take the lead in making a choice. The rest of the group hangs back, "waiting until a threshold number of fish have made a particular decision," Sumpter and his colleagues write [Scientific American].

However, researchers warn that it's not always the best policy to follow the crowd

. In a small number of the team’s experiments, all of the fish in a group chose the “bad” leader. “There’s always a danger of amplifying a bad effect” [Science News]

, comments biologist Stephen Pratt. For an example, researchers say, just look at the bad decisions made by financial institutions over the past few years, which have led to the current economic crisis. Clearly those bankers followed the wrong stickleback. Image: Wikimedia Commons

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