A Strange Nematode in Mono Lake That Has Three Genders

A new species of nematode has recently been discovered in California’s Mono Lake. According to researchers at the California Institute of Technology, the worm has three genders. In addition, it can survive an arsenic level that is 500 times greater than the level that kills humans and it carries its young inside its body. It sounds like a fascinating creature.

Members of the phylum Nematoda are also known as roundworms. Though they are often referred to as “worms”, they aren’t closely related to earthworms. They do have a slender and elongated shape, however. They are common animals. The group contains both parasites and free-living species that live in a wide variety of environments. They range from microscopic in size to several feet in length. The photo below shows a different species of nematode from the ones discovered in Mono Lake, but it gives the general idea of a roundworm's appearance.

A scanning electron micrograph of a soybean cyst nematode and its egg
Agricultural Research Service, public domain license

Mono Lake is located near the town of Lee Vining in Mono County, California. Like the nematodes that live there, the lake is interesting. It has a surface area of around 70 square miles and has no outlet. Its salinity is three times greater than that of sea water. Its pH of 10 makes it an alkaline or basic environment. Despite its seemingly inhospitable nature, the lake contains life. Caltech researchers have recently discovered that eight species of nematodes live in the lake, including the one described above. Before the discovery, only two animal species (a brine shrimp and a diving fly) plus algae and bacteria were known to live in the lake. The newly-discovered nematodes include predators, parasites, and ones that “graze” on microbes. 

An aerial view of Mono Lake in California
Ron Reiring, CC BY 2.0 license

The researchers have been able to culture one of the eight nematode species that they discovered in the lake. They’ve placed this animal in the genus Auanema but haven’t given it a species name yet. Its resilience to arsenic may be an adaptation that enables it to survive in the lake. It’s classified as an extremophile, or one that can live under extreme conditions compared to those required by humans. Its mouth structure suggests that it’s a microbe grazer.

The species exists in three forms: female, male, and hermaphrodite. A hermaphrodite contains both female and male reproductive organs. The eggs hatch inside the roundworm that bears them, who gives birth to live young. A relative of the species in Mono Lake (Auanema rhodensis) also exists in three forms. In this species, the females produce eggs, the males produce sperm, and the hermaphrodites can produce eggs and sperm. The identity of the chromosomes in the gametes, and the possible genders of the offspring in each parental combination appear to be unusual, however. The species was first discovered in 2018 and is still being studied. The studies might apply to the species found in Mono Lake, though this isn’t necessarily true.

Learning about the living creatures in the lake is a very interesting endeavor and could also be useful, for multiple reasons. Understanding how the animals survive in their seemingly harsh environment could be important with respect to organisms that have benefits for humans. Understanding the details of the worm's reproductive system could also be important, even with respect to human biology. 

It’s not outside the realm of possibility that understanding chromosome behaviour in nematodes could explain some situations in humans. The species has X and Y sex chromosomes, as humans do. In general, the cells of female humans have two X chromosomes and the cells of males have an X and a Y chromosome. Some of us have a slightly different chromosome collection, however. The variations in Auanema may help us to understand this situation and perhaps even lead to benefits in humans. Even if this isn't the case, the new species of Auanema sounds like an intriguing animal that is worth studying.

References

• Otherworldly worms detected in Mono Lake from the Science Daily news service
• Some facts about nematodes from the Encyclopaedia Britannica
• Information about Auanema rhodensis from the phys.org news service
• Mono Lake facts from Carleton College

George the Hawaiian Tree Snail and Why His Death Matters

George the Hawaiian tree snail died on New Year's Day, 2019. He was the last of his species known to exist, which means that the species (Achatinella apexfulva) is very likely extinct. George was born in a captive breeding facility and spent his entire life there as scientists tried to save him and his companions. He was named after Lonesome George, a Pinta Island tortoise who was the last of his kind. Lonesome George died in 2012 and was believed to be just over a hundred years old. Many more of the world's land snails are in trouble besides the ones in Hawaii. It's a worrying situation.

Tree snail shells collected circa 1933 and displayed at the Bernice Pauahi Bishop Museum

Credit: Hiart, public domain license

Some Facts About Land Snails

• Snails belong to the phylum Mollusca and the class Gastropoda. 
• Land snails such as O'ahu tree snails (their official name) have a coiled shell. They are able to retract into the shell for protection. 
• The animals breathe by means of a single lung. 
• Gases enter and leave the lung via an opening called a pneumostome, which is located on the right side of the body. 
• The snails have a specialized tongue called a radula. The radula contains rows of tooth-like structures that enable it to act as a rasp. 
• A snail moves by means of a muscular foot travelling over a layer of mucus that it deposits on the ground.

O'ahu Tree Snails

O'ahu tree snails belong to the genus Achatinella and are endemic to Hawaii. According to a Government of Hawaii document published in 2005, 41 species may have existed at that time. The document says that all of the species in the genus were endangered and about half of them were believed to be extinct. The exact number that exists today is uncertain, but it's almost certainly much less than 41. This is a sad comment about a type of snail that was once abundant in Hawaii. Hundreds of species existed at one time.

Some species of tree snails survive today, some that were thought to be extinct have been rediscovered, and some new species have been discovered. Nevertheless, the group as a whole is in trouble. Researchers say that wild populations need to be protected and that if this can't be done members of the species need to be brought into captivity to enable them to survive.

As their name implies, O'ahu tree snails live in trees, though they may also be found in shrubs. They have striped shells and are often attractive. Most species are thought to be nocturnal. They feed on the fungi, algae, and other organisms that grow on leaves but don't eat the leaves themselves. They can live into their teenage years and don't reproduce until they are three to five years old. They give birth to relatively few offspring (less than ten) per year. The youngsters are born live. Only one is produced at a time.

Based on their occurrence in Native Hawaiian stories and their use in leis, O'ahu tree snails must have been very abundant when Polynesians arrived in Hawai'i. Quote from The Government of Hawaii O'ahu tree snail fact sheet

Achatinella apexfulva from 1850

Credit: Naturalis Biodiversity Center and Wikimedia Commons, public domain license

Why Are the Animals in Trouble?

Researchers believe that several factors are responsible for the decline in tree snails. These include loss of natural habitat, the introduction of rats, and the introduction of the rosy wolfsnail, or Euglandina rosea, in 1955. This snail is a carnivore and a predator. It was introduced in the hope that it would eat the giant African land snail, a huge snail that feeds on agricultural crops and is a major pest. The rosy wolfsnail does eat giant African land snails, but it eats lots of tree snails as well.

National Geographic recounts a sad tale that demonstrates the swiftness of the disappearance of one species of Achatinella. The last population of Achatinella lila was counted three years ago. Around 300 snails in the species were living on a particular ridge. In April of last year, no animals could be found and the species was classified as extinct in the wild.

A Snail Named George

George was born at a University of Hawaii captive breeding facility. Not long after his birth, the other captive snails of his species—including adults and youngsters—died for an unknown reason. The researchers tried to find a mate for George but were unsuccessful. He died at the age of fourteen.

Technically, gender doesn't apply to the snails because they are hermaphrodites (animals having both male and female reproductive organs). The presence of another snail is required in order for reproduction to occur, however. The researchers chose to call George a "he." He was only around an an inch long, but he was an important animal.

Some people may wonder why the loss of a snail species is significant. A biologist who was once involved with the captive breeding of tree snails explains why in the quote below. Nature is poorer for the loss of one of its abundant components.

Anything that is abundant in the forest is an integral part of it. Quote from Michael Hadfield, biologist 

A species has a unique set of genes that may be very useful in its environment and enable the species to play an important role there. From a selfish point of view, it may also be useful to humans. The study of genes and gene combinations found in other animals can sometimes show researchers features that might help our lives.

Genetic material was obtained from George's foot. It might be possible to one day produce his species again by a cloning process, which offers a glimmer of hope. The breeding facility has other species of O'ahu tree snails besides George's, and some are doing quite well. It might be possible to increase the population of at least some species in the genus significantly. The animals may have to stay in a breeding facility or be released into an enclosed area protected from rats and predatory snails, however. Perhaps the future situation will be better than the present one.

References

O'ahu tree snail facts from the Government of Hawaii

George the tree snail dies from National Geographic