Ambidextrous' Rainbowfish Are Braver Than Their Peers, Perhaps Because They Think Slower

By Ben Wolford on April 10, 2014 11:05 AM EDT

The most courageous rainbowfish think with both sides of their brain. (Photo: Shutterstock)

The most courageous rainbowfish think with both sides of their brain. (Photo: Shutterstock)

Most of us whose bodies are symmetrical prefer one side to the other. We step into our pants always with a particular foot or write with a particular hand. That's called cerebral lateralization, and many vertebrates do it, including rainbowfish. When presented with a mirror, some of them exclusively look at themselves with one eye or the other.

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Then there are those who think with both sides of their brains — they have no motor preference. That's called non-lateralization, and scientists in Australia recently discovered that these rainbowfish (the black-lined variety) are more courageous than their lateralized peers. It was the first time that fish "ambidextrousness" (as it were; they lack hands) has been linked to behavior. More importantly, their research, published Thursday in Behavioral Ecology and Sociobiology, deals with a deeper question: What makes someone or something bold?

In studying the bravery of threespine sticklebacks, a tiny fish whose name is a tongue-twister, M.M. Webster wrote that "individuals can behave strategically, acting boldly in situations when doing so is adaptive, whilst avoiding risk when the rewards are correspondingly lower." In other words, the going theory is that bolder animals will forage for food longer, even in the face of predators. Whether that courageous behavior is learned or evolved is an open question.

One boldness study of yellow-bellied marmots (their name itself is a tally in the coward column), researchers watched a group of these squirrel-like animals over the course of nine years. To measure their courage, they tested how long individuals stood their ground in the face of approaching danger. They also measured docility by observing their reaction to being trapped. Their results, published in 2013, suggest that infant marmots are more likely to be bold, then lose their edge in old age.

"Personality traits may facilitate animal's coping with age-dependent requirements and constraints," they authors wrote. The study suggests boldness is learned; it's nurture, not nature. Another recent study on dogs showed the same thing. Dogs become less bold as they grow older, and non-neutered dogs were more bold than neutered ones.

So rainbowfish. Unlike dogs, a wild rainbowfish has predators. It must weigh the risks of foraging among predators with hiding, hungry, till the coast is clear. To confirm that wild rainbowfish are more bold than aquarium-bred they timed how long it took them to emerge from a safe hiding place. As expected, the wild ones came out faster, according to a summary of the findings.

Then they subjected the fish to an old vanity test: when presented with a mirror, on which side did the rainbowfish prefer to examine his or herself? This told researcher whether the fish was lateralized or non-lateralized. Afterward, they did the same boldness test and discovered the non-lateralized fish came out faster. They seemed impervious to fear as a direct result of the way they think.

The authors believe that this may be because lateralized brains process information faster than non-lateralized brains do, suggesting the bold fish are only bold because they're too dumb to realize they should be afraid. According to the summary, "The researchers think this may result in a reduced level of fear generally, or perhaps the decision to explore is already made before the moderating effect of fear comes into play."

Above photo courtesy of Shutterstock

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