It may not be what the Spice Girls envisioned when they sang 2 Become 1, but scientists have found that comb jellies actually fuse when injured.
Researchers studying a species of the gelatinous marine invertebrate known as “sea walnuts” said they made the discovery after spotting an unusually shaped individual in the laboratory tank.
“I was very excited,” said Dr Oscar Arenas, co-author of the work, from the University of California, Berkeley.
Write in the journal Current Biologythe team reports that, among other features, the creature appeared to have two “aboral tips,” or rear ends.
In addition, Arenas said, the animal had two jaws – something the team had never seen before.
“It made us wonder if it was the result of two independent animals merging,” he said. “That same evening we began to repeat this observation.”
The team took pairs of sea walnuts – collected at different times from different locations – and removed part of the side of the body for each. Each pair was then pinned together overnight with their injuries touching.
The results revealed that the individuals merged in nine out of 10 cases.
“Once we realized that we could consistently reproduce the fusion, we shortened the time, and eventually we found that the fusion occurred within a few hours in a petri dish,” Arenas said.
The team notes that this is not the first time the transplantation of comb jellies – or ctenophores – has been reported, but they say their experiments expand on such observations.
Among other things, the team found that when they bumped one side of the fused creature, both individuals jerked and contracted, a result that suggests the nervous systems of the pair had fused, they say.
Arenas said the finding was exciting because very little is known about the xenophore nervous system.
“Furthermore, since ctenophores are now considered to be descendants of the ancestors of all other animals, studying how their nervous system works is essential to understanding the basics of neuronal function,” he said.
“In addition, our observations suggest that ctenophores can serve as an excellent model to investigate evolutionary processes of self-recognition systems and advance our understanding of tissue transplantation and regeneration in many tissues, including the nervous system.”
The idea that the nervous systems had fused was supported by the discovery that, one hour after the comb jellies were mated, their muscle contractions began to synchronize. An experiment involving six fused pairs suggested that 95% of contractions within each pair were completely synchronous after two hours.
The researchers found that when they fed fluorescently labeled food to one of the scallops, particles entered the digestive system of the other. However, the digested waste products were expelled from both anuses in an unsynchronized manner.
Arenas said the study suggested comb jellies have few mechanisms to distinguish their own tissues from those of others of the same species.
“I am convinced that this provides insight into the molecular mechanism of how single cells recognize themselves when they fuse to become multicellular animals.”
