For one species of comb jelly, survival after injury may come down to numbers. Two Mnemiopsis leidyi– i.e the sea walnut–can merge and turn into one after injury. These bioluminescent ctenophores will then quickly synchronize their muscle contractions and even merge their digestive tracts to share food sources. The findings are detailed in a study published Oct. 7 in the journal Cell Press Current biology.
“Our findings suggest that ctenophores may lack a system for allorecognition, which is the ability to distinguish between themselves and others,” said Kei Jokura, co-author and biologist at the University of Exeter in the United Kingdom and the National Institutes of Natural Sciences. in Okazaki, Japan, said in a statement. “Additionally, the data imply that two separate individuals can rapidly merge their nervous systems and share action potentials.”
[Related: Comb jellies won’t give into the extreme pressures of deep-sea life.]
Comb jelly makeup over 100 known species in the phylum ctenophora. These small, oval-shaped marine invertebrates use eight rows of comb-like plates moving through the water. Their bioluminescent blue-green “combs” will illuminate both coastal shores and the dark depths of the ocean’s Twilight Zone. They are known to eat other ctenophores and salps, while they eat fish, turtles, marine mammals and more eat comb jelly. Comb jellies also seem to be able to fuse.
The team about this new study saw their unique form of bodybuilding in action while maintaining a population of comb jellies in a seawater tank in the laboratory. They saw an unusually large individual that appeared to have two butts and two apical organs. Jellies typically have only one of these sensory structures, so the team was curious to see if this creature with double appendages was the result of two injured jellies fusing together.
The team then removed part of the lobe of the comb jelly and placed them in groups of two close together. Nine times out of tenthe injured individuals became one and survived for at least three weeks.
Additional research showed this after one nightthe two original individuals seamlessly became one without any clear separation between them. When they poked one lobe, the entire fused body reacted with a striking startle response. According to the teamthis suggests that their nervous systems were also completely fused.
“We were surprised to see that mechanical stimulation on one side of the fused ctenophore resulted in a synchronized muscle contraction on the other side,” says Jokura.
The fused comb jelly also showed spontaneous movements during the first hour. The contractions of each lobe then began to synchronize more. After two hours, 95 percent of the fused animal’s muscle contractions were completely synchronous.
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Their digestive tracts were also fused. The team fed them fluorescently labeled brine shrimp so they could monitor it during digestion. When a mouth ate a brine shrimp, the digestive particles made their way through a molten canal. The comb jelly eventually expelled the waste products from both anuses. However, they didn’t poop at the same time.
According to the teamit is still unclear how the merger of two individuals into one works as a survival strategy. Future studies could help fill these gaps, with potential implications for regenerative research.
“The allorecognition mechanisms are related to the immune system, and the fusion of nervous systems is closely linked to research on regeneration,” says Jokura. “Unraveling the molecular mechanisms underlying this fusion could advance these crucial areas of research.”
