Sex-Changing Snails In Close Quarters Switch Sooner, Researchers Say

Many animals -- snails known as slipper limpets, for example -- change sex when they reach a certain size. While these marine snails may begin life as males, they become female as they mature and develop. In a recent study, Smithsonian researchers discovered contact between snails, rather than chemical cues in the water, triggers this sex change. 

"I was blown away by this result," Rachel Collin, co-author and staff scientist at the Smithsonian Tropical Research Institute (STRI), explained in a news release. "I fully expected that the snails would use waterborne cues to see their world."

Tropical slipper limpets, Crepidula marginalis, live under rocks in shallow intertidal areas along the shore and eat plankton and other particles from the water through filter feeding. Their thin, flattened shells have a built-in shelf that resembles "slipper," hence their name. Often found in clusters, they occur alone or as pairs or trios consisting of a large female with one or two smaller males riding piggyback on her shell. 

For their study, a pair of male slipper limpets were kept in small cups containing seawater. In some cups they were allowed to touch, while in others they were kept separate by a mesh barrier that allowed water to pass through. When two males were kept together and able to touch one another, researchers found the larger one changes to female sooner, and the smaller one later. 

Based on their findings, researchers concluded the snails start out as larger females and change to males because it is advantageous that the large animals are able to produce larger numbers of eggs as females, while small males can still produce plenty of sperm and expel much less energy doing so.

Comparatively, other sex-changing animals -- coral reef fishes, for example -- are influenced by visual, behavioral and chemical cues. Since slipper limpets are rather sedentary animals and have poor vision, researchers expected the snails to depend more on waterborne chemical cues, which are already known to affect other aspects of their behavior. Surprisingly, however, slipper limpets turned out to be like fishes and were greatly influenced by behavioral interactions or perhaps contact-based chemical cues. 

"Slipper snails don't move around much, so you don't really think of them having complex reactions to each other," Collin added. "But this study shows that there is more going on there than we thought."

Their study was recently published in The Biological Bulletin.

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