New "extremophile" worm species found to have three sexes
A bizarre new species of nematode has been discovered living in one of the most inhospitable environments on Earth. These microscopic worms were found in Mono Lake in California, which is three times saltier than the ocean, and are able to survive huge doses of arsenic. But strangest of all, the worms are divided into three sexes – female, male and hermaphrodites.
Mono Lake is famously unfriendly to life, with huge amounts of salt and arsenic. In fact, prior to this study only two other animal species – brine shrimp and diving flies – were known to live in its waters.
Now a team from Caltech has found eight species of nematodes – microscopic worms which are among the simplest and most common animals on Earth – living in the lake. To survive there, all of these species were found to have high levels of arsenic resistance, making them “extremophiles.” They fill different roles in the ecosystem, with some living off microbes, while others are parasites or predators.
One of these worms in particular stood out. Given the temporary name Auanema sp., this creature is a new species and is particularly well-adapted to the harsh environment of Mono Lake, able to withstand 500 times more arsenic than the lethal limit for humans.
But perhaps the most surprising thing about Auanema sp. is that it’s found in three sexes – male, female and hermaphroditic. While hermaphroditism is relatively common in the world of invertebrates, this new worm species does things a little differently.
Among these species, there are a few different ways the phenomenon plays out. In some cases, every member of a species is born with both male and female genitalia for life, and can either reproduce alone or sexually, fulfilling the role as either sex. In other species, individuals can switch between being male and female as needed to fill gaps in a population.
But in this case, Auanema sp. incorporates hermaphrodites as a third sex, appearing in roughly equal measure alongside traditional males and females. Hermaphrodites can reproduce on their own, while the males and females need to mate sexually. The team found that mother worms tended to give birth to male and female offspring early on in their reproductive cycles, but as they got older they would give birth to hermaphroditic babies.
"One potential explanation for this three-sex life cycle is that the females and males could help maintain genetic diversity through sexual recombination, while the hermaphrodites could disperse into new environments and establish new populations there — since they can grow a population by themselves,” says James Siho Lee, co-first author of the study.
The next steps are to sequence the genomes of these worms, to find out how they’re able to survive in such harsh environments.
The research was published in the journal Current Biology.