Science News

Fish elect leader based on looks

Thu, 13th Nov 2008

Part of the show Soothing Music and the Bordeaux Bacterial Bouquet

We’re still feeling the afterglow of the most anticipated election on earth, but now it’s time to turn out attention to the world of fish – sticklebacks in particular. Researchers at Sydney University in Australia have found that when sticklebacks choose their leader, they go for looks.

Red-Lipped BatfishWriting in the journal Current Biology, Ashley Ward and the team found that the fish preferred to follow larger leaders over small ones, fat over thin, healthy over ill, and so on. They also found that the preferences grew more noticeable as the group of fish got bigger, suggesting some kind of social feedback mechanism at work.

David Sumpter of Uppsala University in Sweden also worked on the project, and explained that “Some fish spot the best choice early on, although others may make a mistake and go the wrong way. The remaining fish assess how many have gone in particular directions. If the number going in one direction outweighs those going the other way, then the undecided fish follow in the direction of the majority."

So the fish effectively reach a consensus about who’s the boss, effectively electing their leader.  This is in contrast to many other social groups of animals in which one or a very small number of group members make a leadership decision, which is likely to reflect only their opinions.

To make the discovery, the researchers showed sticklebacks two fake fish differing in characteristics, including size, fatness, shade, and spottiness, that reflect something about the health or fitness of the individual. For instance, a plump belly can indicate success in food gathering, while spots may indicate a parasitic infection.

He then ran trials in which one, two, four, or eight sticklebacks had to choose between two replica fish, one of which had been shown to be more attractive on the basis of the team's earlier studies. As group size increased, the fish made more accurate decisions, choosing between subtle differences in the replicas' appearances.Although the fish mostly made the right decision, following the better looking replica, it sometimes went wrong.  In a substantial minority of trials, all or all but one of the fish followed the less attractive leader.

And in case you were wondering how this might be applicable to anything other than fish, the researchers point out that quite a lot of human behaviour depends on consensus, such as the stock exchange or runs on banks – deciding whether to buy or sell shares, or to take your money out or not. Watching others and copying them if enough individuals seem to be doing the same thing is generally a good behavioural strategy for picking a leader or staying alive, but it may not be so sensible in today’s economic climate.

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