Understanding how an endangered species breeds and reproduces can be one of the first steps toward learning how to save it from extinction. A team of scientists working to conserve the nearly extinct sea snail known as the ribbed Mediterranean limpet (Patella ferruginea) have discovered an important clue about its reproductive strategy: it can change its sex from male to female and back again.

In some ways this isn't unusual. Most limpet species are hermaphrodites, possessing both male and female characteristics, and change sex at one point in their lives, often due to external environmental factors. "As a reproductive strategy, this term means that youngsters, when they reach sexual maturity, do so as males and then, at some point during their vital cycle, change sex and become females," lead researcher Javier Guallart from Spain's National Museum of Nature Sciences explained in a press release.

But the ribbed Mediterranean limpet sometimes takes it one step further by, apparently, switching gender once again. Guallart and his fellow researchers discovered this during a multiyear study of the species that required tagging limpets in their few remaining habitats (the Chafarinas Islands off the coast of Morocco) and returning year after year to carefully determine their sex.

This wasn't an easy task. Mediterranean limpets only reproduce once a year and, as an endangered species, they must be handled very carefully to ensure their safety. Limpets don't display external sexual characteristics, so Guallart and his team tested them by taking a needle biopsy of their gonads. The samples contained either oocytes (egg cells) or sperm, indicating their sex at the time.

The first phase of this research, completed in 2010 and published in 2011 in the Journal of Molluscan Studies, confirmed that some of the limpets changed from male to female. Previous research had theorized this gender-switch for the species but this was its first confirmation. At the time Guallart and his co-authors suggested that the sex change may occur due to a lack of females in the population.

As the work continued, though, the researchers found something unexpected: One of the limpets that had previously switched from male to female switched back again to male. The new results were published earlier this year in Invertebrate Reproduction and Development. The authors wrote that this phenomenon has been seen in some other species, including a few other types of snails, but exactly how, when and why the ribbed Mediterranean limpet makes multiple sex changes remains a mystery.

As the authors wrote in their paper this discovery provides "new direction for research into the mechanisms and factors driving sex change and its effects on the population dynamics" for the species, which may help to inform conservation strategies to keep it from extinction. "There is still a long way to go" to save the species, Guallart said. The limpet is the most endangered marine invertebrate in the region following decades of habitat loss and collection for their shells.