The discovery of body fusion among comb jellies occurred unexpectedly during routine laboratory research conducted by a team led by Kei Jokura at the University of Exeter and Japan’s National Institutes of Natural Sciences.
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Researchers noticed an unusually large individual in the tank, which, upon closer inspection and it was identified as two intertwined warty comb jellies (Mnemiopsis leidyi), showing no apparent separation between them.
Scientists observed an atypical individual of Mnemiopsis leidyi in a laboratory tank that exhibited two aboral ends and two mouths. This peculiar morphology questions about its origin.
The research team was led by Dr. Oscar Arenas and Dr. Kei Jokura, speculated that this unique individual might have resulted from the fusion of two separate jellies after injury.
To test their hypothesis, the researchers collected pairs of sea walnuts from various locations and times. They deliberately inflicted injuries by removing parts of their bodies.
The injured individuals were then pinned together overnight, ensuring their wounds were in contact. The team found that fusion occurred in 90% of the cases.
The researchers discovered that the fusion process could take place in as little as a few hours when the jellyfish were placed in a petri dish.
This response underlines an adaptive mechanism. The fused individuals not only survived the procedure but thrived for at least three weeks, showing a functional integration of their physiological systems.
Upon probing one side of the fused organism, both individuals responded suggesting that their nervous systems had merged. This provided evidence of neurological integration.
The experiments revealed that within two hours of fusion, 95% of the muscle contractions in the fused body synchronized.
Initially, the fused entities exhibited spontaneous movements, but these evolved into coordinated contractions, a level of neurological connectivity previously unobserved in ctenophores.
The fusion process was believed to be a response to injury, as the two jellies merged after sustaining damage. Researchers replicated the fusion by intentionally injuring several comb jellies and pairing them resulting in successful fusion in 9 out of 10 pairs.
The fused jellies demonstrated neural integration within two hours of merging, poking one part of the body elicited a response across the entire fused structure.
This suggests that the nervous systems of the individuals had fully integrated. Feeding experiments revealed that when food was provided to one jelly, it was observed moving through the shared digestive tracts.
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The ability of two separate ctenophores to merge without tissue rejection challenges previous understanding of immune systems particularly the concept of allorecognition, how organisms identify self versus non-self tissues.
This discovery opens up new avenues for exploring the evolutionary development of nervous systems and immune responses, as this behavior has not been documented in other animal species.
Comb jellies are gelatinous, blob-like creatures characterized by their distinctive comb-like tentacles and bioluminescence, which enables them to produce light in the dark depths of the ocean.
They are considered some of the earliest living creatures, having branched off from the common ancestor of all animals. Their unique biological structure makes them essential for studying animal evolution.
Despite being separate organisms with distinct DNA, fused individuals behaved as though they were a single entity, moving and responding to stimuli collectively. This behavior invites questions about the boundaries of individuality among organisms.
The researchers speculate that this fusion behavior is likely rare in the wild due to the necessity of injured individuals being in close proximity to one another.
The researchers plan to conduct further studies on other comb jelly species such as Bolinopsis mikado, to determine if they exhibit similar fusion abilities.
While the study focused on pairs of jellies, there is speculation that more than two individuals might also fuse, warranting further investigation.
Comb jellies have shown regenerative capabilities, allowing them to recover from injuries by regenerating lost body parts. Previous studies indicated that comb jellies can revert to a larval-like stage under certain conditions.
The study explored the digestive systems of the fused jellies, revealing that when one jelly consumed fluorescently labeled food, the particles passed into the digestive tract of the other.
Interestingly, while the fused jellies shared digestive processes, their waste expulsion occurred unsynchronized, showing some level of individual autonomy even within a fused entity.
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