Researchers at the California Institute of Technology (Caltech) have discovered the process at how jellyfish are able to regenerate new tissue in order to repair damages to its body.
Caltech scientists Lea Goentoro, Michael Abrams and Ty Basinger investigated how moon jellyfish (Aurelia aurita) respond to injuries similar to an injured hydra. They focused on the sea creature's ephyra, or juvenile, stage because of the simplicity of its anatomy.
At this stage in its development, the moon jellyfish has a disk-like body surrounded by eight symmetrical appendages, making ideal to clearly show any regeneration of tissues.
The researchers conducted amputations on anesthetized ephyra to simulate injuries that could be caused by predators in the wild. They produced jellyfish that had varying number of limbs instead of the usual eight tentacles.
After the amputations, the animals were returned to their artificial seawater habitat and observed for potential tissue responses.
As expected, the injuries on the moon jellyfish healed up within a few hours, but unlike what was initially thought, the creatures did not regenerate new tissue to replace missing arms. The ephyra had instead reorganized its remaining arms to be symmetrical and arranged them evenly on their disk-like body within the first two days after sustaining the injuries.
The jellyfish initiated this resymmetrization regardless of how many appendages they still had. This was also seen in three other species of ephyra jellyfish.
"This is a different strategy of self-repair," Goentoro said.
"Some animals just heal their wounds, other animals regenerate what is lost, but the moon jelly ephyrae don't regenerate their lost limbs. They heal the wound, but then they reorganize to regain symmetry."
Experts believe there are several reasons why it is important for creatures such as moon jellyfish to maintain symmetry rather than regeneration of limbs.
The body structure of jellyfish feature an arrangement known as radial symmetry, wherein the animal has a distinct top and bottom portions, but it does not have distinguishable right and left sides, qualities that are present in bilateral symmetry.
Abrams explained that this radial form of symmetry is what allows jellyfish to eat and move in the water.
The jellyfish achieve movement in the water by flapping its arms, Abrams said. Their appendages are covered with a thick substance that allows the creatures to paddle continuously. To maintain the fluidity of their movement in the water, jellyfish cannot have large gaps between arms.
The importance of symmetry was also observed when around 15 percent of the total number of ephyra jellyfish the researchers observed did not symmetrized. The animals were not able to reach their adult stage known as medusa.
The findings also showed that for the jellyfish to repair the damage on their body, they did not produce new cells to replace dead ones. Instead, the muscles of the creatures contracted to trigger the symmetrization.
"Symmetrization is a combination of the mechanical forces created by the muscle contractions and the viscoelastic jellyfish body material," Abrams said. "The cycle of contraction and the viscoelastic response from the jellyfish tissues leads to reorganization of the body."
Aside from providing a better understanding of how self-repair works in animals, the researchers also believe their findings can help engineers develop biomaterials that are capable of repairing itself by regaining its functional geometry.
The California Institute of Technology study is published in the journal Proceedings of the National Academy of Sciences.