As any pet owner will tell you, humans aren't the only animals with personalities. And it isn't just dogs and cats. In recent years scientists have found that members of many species, from hermit crabs to rats to fish, have unique dispositions, demonstrating consistent behavioral differences over time and across varying situations.
But how do social situations affect individual personalities? University of Bristol biologist Christos C. Ioannou and his colleagues sought to find out by turning to a small fish called the three-spined stickleback, which inhabits brackish coastal waters throughout the Northern Hemisphere. “They're found both as individuals and in social groups in the wild,” making them perfect for personality assessments across different settings, Ioannou says.
The researchers took 80 fish and placed each under a protective cover at one end of a tank. At the opposite end was some food. Crossing the tank to feed would seem risky to the sticklebacks because open water typically exposes them to the threat of predation.
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Each fish behaved consistently over several days. Bolder ones quickly left the safety of the refuge to go for the food. Timid ones took longer to emerge and swam across the tank more cautiously. But when 10 sticklebacks were placed under the cover together, each fish's individual persona faded away. As with humans, the bolder individuals served as group leaders—albeit careful ones. “The first individuals come out relatively quickly, but it almost looks like they realize they're not being followed and so wait for others to catch up with them,” Ioannou says. When separated from the group later on, the fish regained their original personalities. The results were published in September in Science Advances.
The new findings suggest that group dynamics tamp down individual personalities, and the researchers say it is the first time that such suppression has been explicitly linked to an underlying cause: the need to conform when faced with a risky decision.
Animal personality researchers have historically focused on individuals while ignoring the way they behave in groups, and collective behavior researchers have focused on groups while downplaying individual differences, according to University of St. Andrews animal behavior researcher Mike Webster, who was not involved in the work. “What this study really does is bring those two streams of research together,” showing that animal personalities are flexible yet also persistent, he says.