It might sound like an unfortunate and inconvenient superpower, but a species of sea snail known as the slipper limpet appears to change sex from male to female as a result of touching other males. Naturally, this transformation isn’t instant and doesn’t occur with each contact, although it does provide a clue as to how, when, and why these intriguing aquatic snails switch sex – something that has fascinated marine biologists for many years.

Tropical slipper limpets, or Crepidula cf. marginalis, are born as males but become female at some point after reaching maturity. This process is known as sequential hermaphroditism and has been observed in a number of species of sea snail.

According to a recent study, published in The Biology Bulletin, pre-existing theories regarding the mechanisms by which this process is triggered may be incorrect. It had previously been proposed that waterborne chemical communication between individuals provided the signal for this transformation to begin, although it now appears that this may not be in the case. Rather, the new evidence suggests that physical contact between snails plays a vital role in activating the switch from male to female.

To test this, a team of researchers at the Smithsonian Tropical Research Institute placed pairs of male slipper limpets in containers. Some of these pairs were free to make direct physical contact with one another, while others were separated by a permeable mesh across which water was able to flow, although the animals themselves were kept apart.

Limpets in the partitioned cups were switched from side to side, to make sure that they each had contact with the other’s pedal mucus, the sticky substance secreted to assist locomotion. As such, the researchers were reasonably confident that these snails had sufficient access to any vital chemicals released by their fellow limpets that may be involved in prompting the hermaphroditism.

Several species of limpet display sequential hermaphroditism. Ingrid Maasik/Shutterstock

The researchers also made sure that each pair contained one larger snail and one smaller one, since slipper limpets are known to change sex once they reach a certain size. This is because it is advantageous for females to be larger than males, since this allows them to carry a high number eggs. By ensuring this size difference between their subjects, the team could predict which snail would undergo the transformation, and observe the effects of the experiment on those males that did not change sex.

They discovered that the larger snails tended to grow faster and change sex sooner when they were allowed physical contact with other limpets. At the same time, the smaller snails in these pairs delayed their own development and transformation compared to those in the partitioned pairs.

As a result, the researchers concluded that direct contact, rather than just waterborne chemical communication, may partially mediate the sequential hermaphroditism of slipper limpets. Exactly how this contact instigates the process remains unknown, and therefore requires further investigation.

The findings reveal new and unexpected aspects of slipper limpet biology, with study co-author Rachel Collin explaining that she was “blown away by this result,” adding: “I fully expected that the snails would use waterborne cues,” in a statement.