Otherworldly
Worms with Three Sexes Discovered in Mono Lake
September 26,
2019 -- Caltech
scientists have discovered a new species of worm thriving in the extreme
environment of Mono Lake. This new species, temporarily dubbed Auanema
sp., has three different sexes, can survive 500 times the lethal human dose of
arsenic, and carries its young inside its body like a kangaroo.
Mono Lake, located in the Eastern
Sierras of California, is three times as salty as the ocean and has an alkaline
pH of 10. Before this study, only two other species (other than bacteria and
algae) were known to live in the lake—brine shrimp and diving flies. In this
new work, the team discovered eight more species, all belonging to a class of
microscopic worms called nematodes, thriving in and around Mono Lake.
The work was done primarily in the
laboratory of Paul Sternberg, Bren Professor of Biology. A paper describing the
research appears online on September 26 in the journal Current Biology.
The Sternberg laboratory has had a long
interest in nematodes, particularly Caenorhabditis elegans, which uses
only 300 neurons to exhibit complex behaviors, such as sleeping, learning,
smelling, and moving. That simplicity makes it a useful model organism with
which to study fundamental neuroscience questions. Importantly, C. elegans
can easily thrive in the laboratory under normal room temperatures and
pressures.
As nematodes are considered the most
abundant type of animal on the planet, former Sternberg lab graduate students
Pei-Yin Shih (PhD '19) and James Siho Lee (PhD '19) thought they might find
them in the harsh environment of Mono Lake. The eight species they found are
diverse, ranging from benign microbe-grazers to parasites and predators.
Importantly, all are resilient to the arsenic-laden conditions in the lake and
are thus considered extremophiles—organisms that thrive in conditions
unsuitable for most life forms.
The new worm 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 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 Lee.
When comparing the new Auanema
species 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.
This suggests that nematodes may have a
genetic predisposition for resiliency and flexibility in adapting to harsh and
benign environments alike.
"Extremophiles can teach us so much
about innovative strategies for dealing with stress," says Shih. "Our
study shows we still have much to learn about how these 1000-celled animals
have mastered survival in extreme environments."
The researchers plan to determine if
there are particular biochemical and genetic factors that enable nematodes'
success and to sequence the genome of Auanema sp. to look for genes that
may enable arsenic resistance. Arsenic-contaminated drinking water is a major
global health concern; understanding how eukaryotes like nematodes deal with
arsenic will help answer questions about how the toxin moves through and
affects cells and bodies.
But beyond human health, studying
extreme species like the nematodes of Mono Lake contributes to a bigger, global
picture of the planet, says Lee.
"It's tremendously important that
we appreciate and develop a curiosity for biodiversity," he adds, noting
that the team had to receive special permits for their field work at the lake.
"The next innovation for biotechnology could be out there in the wild. A
new biodegradable sunscreen, for example, was discovered from extremophilic
bacteria and algae. We have to protect and responsibly utilize wildlife."
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