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Still a little bit tadpole. Metamorphosis alters nearly everything about a frog, but not its personality.

Christian Fischer/Wikipedia

Changing Bodies but Not Personalities

Some of our personality traits from childhood stick with us for the rest of our lives. An early shyness on the playground doesn't always go away in the boardroom, for example. But what if your entire body changed as you aged, transforming you into a completely unrecognizable creature? Would you retain the personality of your youth? A new study in frogs suggests that you would.

In the past decade, scientists have shown that a broad range of animals—from dogs to sea anemones—display consistent personalities throughout their lives. Despite changes in their environment, individuals maintain their tendencies, such as being more or less active and exploratory, relative to other individuals of their species. But some researchers have theorized that animals that undergo metamorphosis should be exceptions. The full-body transformation, seen in everything from frogs to butterflies, dramatically alters every aspect of the animal—not only its shape, but also where it lives and what it needs to do to survive and reproduce. Why, then, shouldn't metamorphosis also change the animal's personality, so that strengths in larvae don't become flaws in adults? The relative restlessness that helps a caterpillar find food better than its peers, for instance, could get the butterfly into trouble with predators.

Few researchers have attempted to study personality before and after metamorphosis, says behavioral ecologist Alexander Wilson of the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin. He says his new study of frogs, to be published later this month in Behavioral Ecology, is the first to tackle the question in vertebrates. It was hard, Wilson says, to find personality tests that would work well for tadpoles and frogs, which are like two distinct animals. "[They] reach a certain stage of their life and then, bam! They change into something completely different."

Wilson caught the study's 75 wild tadpoles in pools on the edge of a lake near Berlin. He then performed a series of underwater experiments, first on the tadpoles and then on the frogs they became. In one experiment, a test of exploratory tendencies, Wilson placed the tadpole or frog in a new tank and timed how long it took to move for the first time. In another experiment, a test of activeness, he measured what fraction of a 10-minute period the animal spent in motion. Afterward, he released the frogs near the places where he caught the tadpoles.

The data revealed consistencies in most of the amphibians' tested personality traits. In particular, the tadpoles that were more active and exploratory turned into frogs that were also more active and exploratory. Only one test—in which Wilson simulated a predator by squirting water at the animals -- revealed a personality shift; a tadpole that responded by freezing in place for a long time was just as likely to become a frog that resumed normal activities right away.

“This is just really surprising," Wilson says. "They're completely different as juveniles to what they are as adults … [but] there are some behaviors that are consistent."

The work may help settle a major debate about the underlying reason for personality, says behavioral ecologist Michael Taborsky of the University of Bern, who wasn’t involved in the study. Some scientists have argued that personality is an adaptation that helps animals to survive. In that case, it should change with metamorphosis, since the animal's whole world changes. Others say that personality is just a byproduct of the animal's physiology, in which case it would be more likely to remain consistent. A high metabolism, for example, could lead to an active personality, even if it tends to make an animal more visible to predators. The new study, Taborsky says, supports the latter idea. Personality may be nothing more than a side effect of life.