The football-sized crustaceans feast when they can, then slow their metabolism to the point of crawling.
A kilometer deep in the ocean, football-sized roly-polies slowly climb the seafloor. Their metabolism is so slow that they can go years between meals. Now, researchers have discovered a genetic quirk that helps explain the evolution of these colossal crustaceans.
Long ago, these creatures stole a gene from a bacteria and welded it into their own set of DNA. This may help crustaceans tolerate extremely long periods without food in the frigid and abyssal desert, researchers reported on June 5 in Cell.
Isopods are armored, oblong crustaceans. Terrestrial species are commonly called woodlice, bedbugs or roly-polies. Although many isopods are smaller than a pencil eraser, groups of deep-sea species including Bathynoma can reach relatively monstrous proportions, with some reaching almost half a meter in length. These giants seem well adapted to a slow life in the inky black depths where there is little to recover. Some giant isopods in captivity have been recorded going more than five years without eating – one of the longest durations known among animals.
“It’s really remarkable,” says Jianbo Yuan, a marine biologist at the Chinese Academy of Sciences in Qingdao.
After researchers from the Chinese Academy captured some specimens of the giant B.Jamesi with a submersible vehicle near China Hainan IslandYuan and his colleagues wanted to know how these animals could grow to large sizes in such an arid environment. The team compared these deep-sea isopods with a smaller species living 300 meters deep and another even smaller species living along the coastline. The researchers analyzed details of the isopods’ complete set of genetic instructions and their anatomy.
“The results turned out to be even more surprising than we imagined,” says Yuan.
This giant deep-sea species had a truly enormous stomach, filling up to two-thirds of the body cavity, much larger than that of shallower-dwelling species. Researchers believe these giant isopods rarely eat. But when they do, they gorge themselves as much as they can, filling their bellies with carrion and whatever slow-moving animals they can catch.
They also figured out how to make their meals last. Researchers discovered that the genetic code of deep-sea isopods included a few copies of ND1a metabolic gene originally originating from bacteria. The gene passed from bacteria to the genetic instructions of an ancestral isopod more than 16 million years ago. When researchers engineered fish in the lab to ND1this increased their starvation survival rate by 37 percent – but only in cold weather. The gene appears to limit cell energy consumption. This could allow isopods to nourish their large bodies even when food is scarce, Yuan says.
The findings help expand our understanding of how evolutionary innovations develop more broadly, says Yang Li, an evolutionary biologist at the University of Michigan in Ann Arbor who was not involved in the research. Isopods provide an example of how traits are not limited to the evolution of genetic changes. “[The isopods] also acquire and domesticate genes from microbes,” he says.
Li wonders if other ocean creatures have similar stolen genes used to survive the unforgiving depths.
