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Survival in the deep sea is inherently challenging: darkness abounds, the temperature is near-freezing, and food is hard to come by. And yet, instead of withering away in the harsh conditions, many deep-sea animals, from massive spiders to giant squid, adapt by growing large, dwarfing their shallow-water relatives or terrestrial Why these animals get so big has interested scientists for more than a century. Now, by asking a slightly different question: How do they get so big?, scientists are getting closer to an answer.
A team of researchers recently sequenced the genome of the giant isopod Bathynomus jamesi, a first for a deep-sea crustacean. With round, segmented bodies, giant isopods look like roly-polys, except they can grow as long and as heavy as a chihuahua. The team behind the work, led by Jianbo Yuan, a geneticist at the Chinese Academy of Sciences in Beijing, hopes that the details hidden in the animal’s genetic code will help us better understand what goes on behind the scenes, genetically speaking, with the deep sea. gigantism
Analysis of the genes of Bathynomus jamesi indicates how this giant isopod developed the key adaptations that allow it to thrive in the deep. Photo by Jianbo Yuan and Xiaojun Zhang
Giant isopods, or bathynomids, are the jumbo cousins of the armored crustaceans found grinding under fallen logs. While the smallest isopod species measure less than half a centimeter, bathynomids can grow 80 times larger. The niches occupied by isopods are equally varied: there are more than 10,000 known species and they are found everywhere from the ocean floor to caves and mountain tops. This physiological and ecological diversity makes the isopod family tree the perfect place to look for clues about what drives adaptation underneath.
Among the more interesting questions, Yuan says, is whether today’s deep-sea giants simply descended from strong ancestors—animals like anomalocarids, large arthropod predators that existed about 50 million years ago—or whether they evolved more recently under the pressures of life. in the deep sea In the case of giant isopods, their genome points to the latter explanation.
Like their bodies, bathynomid genomes are incredibly large. B. jamesi, the researchers found, has a large number of so-called jump genes, transposable elements that can be moved from one place to another in the isopod’s genetic code. Jumping genes are linked to high mutation rates, which the researchers believe may make the isopod better equipped to deal with environmental stress.
Having a large number of genes is something that B. jamesi shares with other deep-sea invertebrates. That invertebrates (organisms generally considered less complex than vertebrates) have developed some of the most complex and adaptable genetic codes has puzzled scientists since genome sequencing began.
Beyond revealing the size of its genome, scientists delving into the biology and genetics of B. jamesi have also suggested possible explanations for a number of key adaptations the animal uses to thrive in the deep.
The stomach of B. jamesi, for example, can expand to take up two-thirds of its body. This ensures that when it can find food, it can gobble up as much as possible. Yuan and the team also found changes in B. jamesi genes related to thyroid function and insulin, which likely increase the isopod’s ability to grow and absorb nutrients. In addition, they found an adjustment that slows down the breakdown of fat. Keeping extra junk in the trunk allows giant isopods to go years without food.
Alexis Weinnig, a deep-sea biologist and geneticist at the Leetown Research Laboratory in West Virginia who was not involved in the study, says she likes that Yuan and her team are trying to better understand isopods from the deep in through their genes. Living in the deep sea, isopods are hard to find and harder to study in the field. “I think getting into basic genetics will be a big player in understanding the underlying reasons for gigantism,” he says.
Weinnig hopes the find will remind people that beyond their potential to help make sense of a scientific dilemma, deep-sea species deserve the limelight.
“We lose track of how amazing it is that these animals live on our planet,” says Weinnig. “They have to be resourceful at every level … with reproduction, with metabolic processing. Everything has to be used so that nothing goes astray.”