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Late one summer night in 2023, Kei Jokura excitedly entered the Marine Biological Laboratory in Woods Hole, Massachusetts, with a blob in a beaker. The biologist had just returned from the first floor, where there was a colony of gelatinous ctenophores in the tank.
That one was larger than the others and looked like two jellyfish in one. “I couldn’t believe my eyes at first,” recalls Chocula, then a postdoctoral fellow at the University of Exeter in the UK.
Mariana Rodriguez-Santiago, a postdoctoral researcher at Colorado State University, was working on her own project when Jokura showed up. “We were all amazed and thought, ‘How can they fit together and still swim and move as one?'” she said. She grabbed a pipette and poked a jelly. It squirmed. At the same time, so does the one it seems to be attached to. “We thought, ‘Can they feel the same way? Are they one person? Two people? How can we solve this problem?
Over the next few weeks, Rodriguez-Santiago helped Chocura combine pairs of ctenophores (scientifically known as Mnemiopsis leidyi) to see what would happen. The results of the investigation led by Jokura were published in the journal on October 7 modern biologyshowing that two jellyfish can fuse not only their bodies, but also their nervous and digestive systems. The two actually become one.
“The fusion phenomenon does raise many interesting questions, such as which genes are involved in fusion, what happens to neural signals, and what are the definitions of ‘self’ and ‘non-self,'” said Jokura, a postdoctoral fellow at the National Research Institute in Japan. Basic biology. “Each of these topics has the potential to challenge our fundamental understanding of biology.”
Ctenophore Found in coastal waters and deep oceans around the world. Although they look similar to jellyfish, they do not sting and belong to a different phylum, Ctenophorewhich means “comb holder” in Greek. They get their name from their combs, which are rows of hair-like appendages called cilia that they use to move through the water.
Ctenophores are one of, if not the oldest animals on Earth – probably the sister to all other animals on the tree of lifeso “they offer a truly unique opportunity to study fundamental aspects of nervous system function,” said Rodriguez-Santiago, a co-author of the study.
“They belong to a group of animals that existed when the earliest animals evolved,” said Pawel Burkhardt, an evolutionary biologist and researcher at the University of Bergen in Norway. Burkhardt was a co-author of another October report on M. leidyi that was published in the magazine Proceedings of the National Academy of Sciencesshowing that jellies are able to develop backward, returning to earlier life stages after stress. He was not involved in the study published in Current Biology.
“Two recent papers highlight that ctenophores have the opportunity to rapidly adapt to changing environments and that their developmental programs may be more flexible than those of other animals,” he said.
Chocula’s paper suggests that ctenophores may also lack the protective conspecific recognition mechanisms that allow one organism to distinguish its own cells and tissues from those of another organism. For example, in humans, allogeneic recognition underlies organ rejection that occurs during transplantation.
While studying the response of M. leidyi to light, Jokura discovered that two injured individuals were conjoined. To recreate this phenomenon, he and Rodriguez-Santiago began experiments. They cut off portions of several pieces of jelly and placed the cut pairs in a petri dish overnight.
Nine of the ten pairs successfully fused, resulting in animals with two sense organs and two sets of anal openings, compared with only one in typical jellyfish.
It turns out, Chocula says, that fusion occurs much faster than researchers expected. “To see the fusion process—when and how it happens—we performed time-lapse imaging,” he said. The team put the sliced jelly together and waited.
At first, the jellyfish continued to contract its muscles independently. Within an hour, their movements began to synchronize. By two hours, they were in sync. When poked gently on one side, both sides of the combined organism contracted in unison.
The images show another layer of fusion: the animals’ digestive systems also come together. The researchers fed a fluorescently tagged brine shrimp into the mouth of a pair of jellyfish that had been fused for two days. The team then tracked the meal’s movement through a microscope.
The digested particles move along the digestive tract, cross the fusion boundary, and enter the digestive tract of another animal—”and the other animal may excrete the food,” Rodriguez-Santiago explains. Eventually, the waste is excreted through both anuses, each in its own time.
What Rodriguez-Santiago finds most interesting about this study is that it questions what she sees as “pretty strict boundaries” between self and others.
Allorecognition is considered a protective adaptation because it enables the body to reject foreign cells that may introduce dangerous disease. But these animals “get around this sensory rejection and may have a better chance of survival,” she said.
Burkhardt believes the findings may shed light on when animals evolved homogeneous cognition and how simple nervous systems form and process information.
Jokura hopes to further investigate how the jellyfish’s nervous systems work together after fusion. “I wanted to investigate how their ‘ideas’ were integrated,” he said. “By visualizing neural networks, we might be able to explore things like consciousness fusion.”
Correction: An earlier version of this story incorrectly described the name of the Marine Biological Laboratory in Woods Hole, Massachusetts.
Amanda Schupak is a science and health reporter in New York City.