Snails that are held close to each other may undergo sex change with just a simple touch, as discovered in a new study. Big male snails change more rapidly than smaller ones and the change is triggered by contact rather than complex chemical releases.

Sex change is not something very unusual for some animals. In fact, many species undergo sex change at some point in their lives, particularly after reaching a certain degree of maturity or size. Snails called slipper limpets are born male, but they turn into females later in life.

Sex change is believed to be triggered by visual, behavioral, and chemical factors. With the poor vision and sedentary nature of slipper limpets, experts think that sex change depends on waterborne chemical cues, which are previously recognized to affect other behavioral features.

In the study, however, the researchers discovered that the species are like fish because they react more to behavioral contact and chemical factors, rather than waterborne triggers.

"I was blown away by this result," said co-author Rachel Collin from Smithsonian Tropical Research Institute (STRI). She added that she highly anticipated snails to respond to waterborne signals.

To be able to come up with the findings, the authors used two male snails with different sizes. The samples were placed in cups containing seawater. Some of the cups are conducive for free contact while the others contain a mesh division that keeps the pairs apart.

The results of the experiment show that the bigger snails with direct contacts with their partners developed more rapidly and transformed into females sooner than those that were separated by a physical barrier. Meanwhile, the smaller snails with direct contact exhibited more delayed sex change than those with a mesh separation.

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

Tropical slipper limpets (Crepidula cf. marginalis) settle under rocks and intertidal locations along the shore. The species filter plankton and other water particles for food.

The flat and thin shells of the species contain their own shelves. The shells look like men's house slippers when flipped over. The species are most commonly spotted in groups of two or three — one large female with one or two smaller males on top of the shell.

A male limpet usually has a penis that is so long, it sometimes runs through its entire body. The penis inconsistently emerges from the right side of the head. The genital size makes it easier to reach the female's opening.

When a snail turns into a female, the penis eventually shrinks and disappears alongside developing female organs. The pattern is said to be on point as large animals are able to effectively generate egg cells as females, while males can produce plenty of sperm even as a small creature.

The study was published in the journal Biological Bulletin.

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