What Extroverts and Introverts Can Learn From Snails

Genes may change a snail’s “personality” and the thickness of its skin (or rather, its shell)

The wandering pond snail may be small, but it is giving scientists insights into a rather lofty question: Why do we have personality? (© Science Photo Library/Corbis)
smithsonian.com

If you think of pond snails at all, you probably don’t think of them as charismatic, enlightened or behaviorally distinct. But a Swedish ecologist named Johan Ahlgren would disagree. With a little prodding—in this case, with tweezers—he is studying these lowly creatures for insights into a rather lofty question: Why do we have personality?

It’s hard to imagine ourselves without the qualities and quirks that set us apart, but assume for a moment that no matter the situation we all behaved in an optimal way. For hunts out on the savanna, we’d possess the timidity to keep us safe from predators but take risks enough to find the most nutritious foods. In a modern equivalent, we’d work hard at the office to support ourselves without neglecting the time and energy required to find, and impress, a mate. Yet, our behaviors aren’t so robotic; they fall on a continuum.

This is personality, and it adds some unpredictability in the race to survive and reproduce. What’s more, over the past few decades, scientists have found that nonhuman animals have personality, too. Some fruit flies are consistently more aggressive than others. Chimps can be agreeable or difficult. And snails appear to come in bold and shy varieties.

To test why this might be, Ahlgren and colleagues at Lund University tramped out to ponds and gathered small banana-shaped egg capsules with the curls of baby snails just visible inside. For three months after the snails hatched, he fed them a diet of spirulina and lettuce. Then, the tapping began. He placed the 168 snails one by one in a petri dish and lightly hit their shells with tweezers until they hid, presumably fearing a predator (a fish that wants to pry them off the rocks, for example). Ahlgren timed how long it took each snail to poke its head back out. Those that re-emerged in 10 seconds or less were classified as bold, while 15 seconds or more meant shy.

Next the snails took turns sitting on the bed of an Epson 2450 photo scanner. Images of their shells were analyzed for size and shape. The bold group had rounder and thicker shells, more resistant to crushing. Shy snails had narrower, thinner shells.

“The nerd in me got really excited,” says Ahlgren. Tough shells would keep snails safer from predators but would require more energy to build. So their bearers have to be bold to go out and seek food. Thin shells require less energy but they leave their wearers more susceptible to predators, so the snails are shy. “They have a slower pace of life,” Ahlgren says. “They might live longer, and reproduce more than once.” To put it simply, the personalities of the snails were compensating for their physical limitations.

This isn’t the first time personality has been linked with a physical trait. Bold brown anole lizards have tails that break off with less force than those of their more shy peers, for example. The adaptation probably allows them to escape more easily when attacked. But if Ahlgren’s conclusions are correct, the new study is the first time that genetics plays a role in the link. Researchers pulled the snails from fish-free ponds, with no predators to worry about, and fed the snails equivalent diets, so no one had an energy advantage. Ahlgren’s snails, he suspects, must have inherited their personalities from their ancestors.

Ahlgren isn’t suggesting a singular reason for personality, but his work offers the glimmers of insight that make studying this phenomenon in animals so exciting, says Samuel Gosling, a personality researcher at the University of Texas at Austin. Humans have such complex behaviors that isolating just one quality and identifying its source has been a challenging task. Simpler behaviors allow for simpler questions, “questions so fundamental we haven’t asked them,” Gosling says.

Think of it this way: The snails are enduring the prodding so the humans don’t have to. ​

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