Southpaw snails have advantage

Much as human southpaws have an advantage in many sports, a dominant left “hand” lends some snails a competitive advantage in the game of life, according to a recent study.

The study, co-written by geologists Gregory Dietl of Yale and Jonathan Hendricks of the University of Kansas and published in the Royal Society Biology Letters, found that snails with apertures on the left side of their shells, also called sinistral or left-handed snails, are less likely to be eaten by crabs than the more common snails with right-side apertures. The findings of the study, Dietl said, contradict the previously accepted belief that snails with left apertures had no functional advantage or disadvantage in their natural environment.

Dietl said he first considered this line of research when he began to wonder if snails have an upper edge in biology in the way left-handed athletes often benefit from their relative rarity.

“I suspected there might be an advantage to being left-handed, because I immediately thought of every sport,” he said.

Travis Pinick ’09, the only left-handed player on the Yale basketball team, said being a lefty is definitely an advantage for him.

“The majority of basketball players are right-handed,” Pinick said. “Your muscle memory isn’t inclined to guard a lefty.”

Dietl and Hendricks initially examined the scars crabs had left from failed attacks on fossil snail shells, but Dietl said the results were counterintuitive. Left-handed snails were found to have fewer scars than right-handed snails.

“We would have suspected that if it was harder to open left-handed snails, there would be more scars,” Dietl said.

But after working with live snails and crabs in the laboratory, Dietl said, they realized that crabs generally avoided left-handed snails altogether, because the mostly right-handed crabs were unused to seeing snails with a left-handed aperture and had a more difficult time manipulating them.

“Crab species we worked with didn’t even know how to begin,” he said. “They would just rather drop them.”

The advantage of left-handed snails, like that of left-handed athletes, is a product of their rarity, Dietl said, noting that it would not be an advantage if left-handed snails were as common as right-handed snails.

Lefty snails are also limited in their mate selection, Dietl said, where the rarity can actually be a disadvantage because snails must choose mates of the same handedness due to the orientation of their shells. The difficulty for a left-handed snail of finding a left-handed mate, he said, helps explain why lefty snails are not more common.

Hendricks warned against making any overly broad generalizations based on the results of the study.

“One type of handedness can only be considered advantageous or disadvantageous relative to the other type in particular situations,” he said in an e-mail. “Left-handedness probably conferred no other advantages to the sinistral snails, except when they were interacting with the right-handed crab predators.”

Hendricks said he thinks studies based on fossils are important because of the relevance they have to modern organisms.

“Fossils can inform us about how ancient organisms interacted with each another,” he said. “This knowledge helps us to understand the origins of the ecological interactions of modern organisms.”

The findings published in the paper were preliminary, Dietl said, and there is more work to be done in studying the differences between left-handedness and right-handedness in nature.

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