Some organisms do it horizontally, some do it vertically, some do it sexually, and some do it without sex. Then there are some organisms that prefer to grow a back end that develops into an independent member equipped with its own parts like antennae, eyes, and a brain. This member will detach from the main body and swim away, carrying the gonads that will merge with those in other separated back ends and produce new offspring.
What is this thing in the strange star system of sci-fi films B?
In fact, there is really a species called Megasyllis nipponica on Earth. Also known as the Japanese green syllid worm, it reproduces through a process known as stolonization, which sounds like a brilliant idea from a fictional horror world of science fiction but has evolved in some segmented worms to give future generations a better chance of survival. It has still been a mystery (until now) exactly how this strange member, or back end, can form its own head in the middle of the worm’s body. This seems wonderful in terms of genetic organization. But how?
How does it happen?
A team of scientists led by evolutionary biologist and professor Tohru Miura from the University of Tokyo conducted a study to discover the genetic mechanism behind the formation of the back end. It all starts with Hox genes. These are a set of genes that help determine which parts of the embryo will become the head, thorax, abdomen, and so on. In segmented worms like M. nipponica, different Hox genes organize the parts that form the entire body of the worm.
Miura and his colleagues expected that the activity of Hox genes would be different in the front and back parts of the worm. They discovered that it is not actually the Hox genes that control the parts of the back end but rather the development of the gonads that alters its identity. “These findings indicate that the development of the gonads stimulates the formation of the head for the back end, without activating the anterior Hox genes,” the team said in a study recently published in Scientific Reports.
Development of the front and back end
The front end, or main part, of M. nipponica is neither male nor female. The worm has organs called primordia gonads on the underside of the back end. When the primordia begin to develop into eggs or testes, the genes responsible for head formation (different from Hox genes) become active in the mid-region of the main body.
This is when the back end starts developing its head. The head grows a cluster of nerve cells that function as a brain, along with a central nervous system extending throughout its body. Eyes, antennae, and the swimming bristles of the back end also appear. It leaves behind
Development of the back end
Before the back end can swim on its own, it must develop enough to be able to swim independently and find its way to another mate of the opposite sex. The fully developed back end looks like an alien attached to the rest of the worm’s body. In addition to its own nervous system and something akin to a brain, it also has a pair of bulging eyes and a pair of antennae, along with its own digestive tract. These eyes grow for a reason, as the gonads often need to navigate through murky waters.
The antennae of the back end can sense the surrounding environment, but researchers suggest that it has a more important function – detecting pheromones secreted by the opposite sex. Still, the back end is not an exact replica of the main part. It lacks some of the more sophisticated features of the worm, such as a digestive tract that has several specialized regions, perhaps because its sole purpose is reproduction. It dies shortly after.
Development
Rear Part Phenomenon
What can cause the rear part phenomenon to develop in the first place? More research needs to be conducted, but for now, it is believed that this strange ability may arise in some segmented worms when the genes that develop the head extend beyond the body, although it is still unknown why this genetic shift evolved initially.
The worm also regenerates its rear sections at a high rate, which may give it the best chance to reproduce its species. Get ready for a surprise.
Scientific Reports, 2023. DOI: 10.1038/s41598-023-46358-8
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Elizabeth Rayne is a writing entity. Her work has appeared on SYFY WIRE, Space.com, Live Science, Grunge, Den of Geek, and Forbidden Futures. She lurks outside New York with her parrot, Lysat. When she’s not writing, she may be shapeshifting, drawing, or playing a character no one has ever heard of. Follow her on Threads and Instagram @quothravenrayne.
Source: https://arstechnica.com/science/2023/12/bizarre-worm-can-detach-its-own-butt-and-make-it-swim-away/
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