With an average length a little over 60mm, the zebrafish is a convenient mouth-sized snack for its predators, and this constant threat of being eaten has led to zebrafish evolving some speedy reaction times in order to dodge any looming jaws. But in the wild they need more than just quick thinking to avoid becoming lunch, they need an athletic body that can move just as swiftly.

Now, researchers at North Carolina State University have discovered a clear link between the mind and body of zebrafish, which suggests that the fish’s body shape is actually changed by its personality.

Personality test

In order to test this the team needed to separate bold and shy zebrafish by measuring the time spent stationary when introduced into a new tank. Zebrafish that remained still for more than three minutes were considered shy while the bold ones were those who stayed stationary for only 50 fleeting seconds. These two groups were then segregated into separate tanks and bred together.

It took only a few generations before the fish started to exhibit a range of behaviours associated with stressful situations (like becoming lunch), but also (and more interestingly), that bold fish had more elongated bodies and larger tails, facilitating speeder escapes.

However, evolution isn’t a simple process and other factors might be involved, such as recurrent natural selection, where the same trait might evolve via an alternate route. This could result in a process known as linkage disequilibrium, the non-random association of genes at different section of the genome.

“The association between personality and body shape seems to reflect linkage disequilibrium that is not caused by genes affecting multiple phenotypes or physical genetic linkage,” says Brian Langerhans, assistant professor of biological sciences at NC State.

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“That means these traits may owe their association to recurrent natural selection acting on combinations of traits - being bolder and sleeker may help zebrafish survive to adulthood or to mate more successfully, resulting in fish tending to have those combinations of traits/genes.”

Brain training

While it’s well known that multiple factors work together to boost an organism’s survival chances, the links between behavioural and non-behavioural traits are only just starting to be understood. "This is one of the first studies linking personality variation to these other types of traits,” “I think many more will emerge in the coming years".

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