New Species of Microscopic Worm Has Three Sexes, Lives in Arsenic-Rich Lake

An international team of biologists has isolated eight species of nematodes from the arsenic-rich sediments of Mono Lake in the Eastern Sierras of California. One species, temporarily dubbed Auanema sp., is new to science, culturable, has three different sexes, carries its young inside its body like a kangaroo, and can survive 500 times the human lethal dose of arsenic.

Auanema sp. lives in the high-salt, high-pH, arsenic-rich Mono Lake. Image credit: Shih et al, doi: 10.1016/j.cub.2019.08.024.

Mono Lake is three times as salty as the ocean and has an alkaline pH of 10. Before this new study, only two other animal species were known to live in the lake: brine shrimp and diving flies.

In the new work, Caltech Professor Paul Sternberg, University of Haifa’s Dr. Amir Sapir and their colleagues from the United States, Japan, the United Kingdom and Israel found eight more animal species, all belonging to a class of worms called nematodes. Only three of them are known to science.

All eight species are diverse, ranging from microbe-grazers to parasites and predators. Importantly, all are resilient to the arsenic-laden conditions in the lake and are thus considered extremophiles.

“Extremophiles can teach us so much about innovative strategies for dealing with stress,” said Caltech Dr. Pei-Yin Shih, first author of the study.

“Our study shows we still have much to learn about how these 1,000-celled animals have mastered survival in extreme environments.”

One of the new species, Auanema sp., exists in three different sexes: hermaphrodites, females, and males.

The hermaphrodites can produce offspring by themselves, but the females and males need to mate in order to produce their young. The females and males are often produced early in the reproductive cycle of the mother, followed by the hermaphrodites.

“One potential explanation for this three-sex life cycle in Auanema sp. 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,” said Caltech Dr. James Siho Lee, co-author of the study.

When comparing Auanema sp. to sister species in the same genus, the researchers found that the similar species also demonstrated high arsenic resistance, even though they do not live in environments with high arsenic levels.

In another surprising discovery, Auanema sp. itself was found to be able to thrive in the laboratory under normal, non-extreme conditions. Only a few known extremophiles in the world can be studied in a laboratory setting.

“Our findings expand Mono Lake’s ecosystem from two known animal species to ten, and they provide a new system for studying arsenic resistance,” the scientists said.

“The dominance of nematodes in Mono Lake and other extreme environments and our findings of preadaptation to arsenic raise the intriguing possibility that nematodes are widely pre-adapted to be extremophiles.”

The research was published in the journal Current Biology.

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Pei-Yin Shih et al. Newly Identified Nematodes from Mono Lake Exhibit Extreme Arsenic Resistance. Current Biology, published online September 26, 2019; doi: 10.1016/j.cub.2019.08.024