Regeneration Discovery: Benjamin Button Jellyfish
By: Ashley Gustafson
Recently, a surprising discovery was made in China about a seemingly not so surprising moon jellyfish. The moon jellyfish or Aurelia aurita is a common species of jelly fish found in wide ranges in the Atlantic, Pacific, and Indian oceans near the coast in mostly warm and tropical waters. Jellyfish while lacking brains may seem like a simple, well understood animal but in fact there is so much more to them than meets the eye. Like many other Cnidarians, like coral, moon jellies have complex life cycles that feature both sexual and asexual reproduction as well as a significant transformation from juvenile to adult. While the moon jelly’s ability to transform throughout its life time is no surprise, what a graduate student at Xiamen University found was different than expected.
The curious case of Benjamin Button
Just in case you aren’t familiar with the Benjamin Button concept, it is the idea of growing up backwards. That is, beginning life as elderly and ending life as an infant. In the infamous Benjamin Button tale by F. Scott Fitzgerald, the character of Benjamin Button is born a man and ends his life a baby. The concept has been portrayed in movies and stories the most famous featuring Brad Pitt as Benjamin Button. Like the story of Benjamin Button, the discovery of this moon jelly’s regeneration abilities was a very curious case indeed.
Regeneration found in wild-caught Moon Jelly
Earlier this month, Jinru He, a graduate student at Xiamen University in China made the discovery of a lifetime. It began with He raising a juvenile male moon jellyfish that he captured from the ocean. When the male moon jelly died, he placed it in an empty, new tank. Then, three months later he noticed a polyp appear on the deceased male moon jellyfish and he couldn’t believe eyes. What could this mean? He’s observation was the first of its kind and has been interpreted as an event similar to a caterpillar first sprouting its butterfly wings; that is a life cycle transformation event.
Moon Jelly Life cycle
Like most species of jellyfish, moon jellies have a cyclic life cycle which means they go through life stages. Now these life stages aren’t like the ones we go through as humans; they are much more dramatic in terms of change and body design. Jellyfish are truly masters of transformation. First, they begin life as fertilized eggs which become planula or larvae (sexual reproduction). Then the planula develops to be a polyp which can bud (asexual reproduction) and create more polyps. Polyps will then become strobila. The Strobila then emerges as an Ephyra or young medusa which eventual matures to a medusa or adult stage of a moon jelly. He’s observation was different than the expected moon jelly life cycle because many jellyfish bud off polyps seen on the ocean floor or a coral reef but the conception of a polyp forming from a deceased medusa has never been recorded and observed before.
Putting the Pieces together
Since He’s discovery, it has been found that injured and dying medusa’s will swim to the bottom of the ocean floor so that they can transform or regenerate themselves back to the polyp or infant stage of life and “grow up” again. While slightly different than the curious case of Benjamin Button the parallels are quite obvious. While the character of Benjamin Button ages backwards, he still only ages unidirectional (old to young) it appears as though the moon jellyfish can age in any direction they so choose (young to old to young and so on).
This unprecedented life cycle allows moon jellyfish to achieve the polyp stage from both the planula or larval stage and the medusa or adult stage. As I mentioned previously, while this multi-directional life cycle is a new discovery, moon jellyfish have been known for their powers of transformation from tiny free-swimming larvae to stationary polyps back to free-swimming sexually mature medusas. While they seem to be able to regenerate themselves at a time of great injury they cannot simply regrow limbs that they lose. As found by Caltech researchers, they instead reorganize their bodies to stay symmetrical and this has even been witnessed in medusas with as few as two limbs left. This reorganization may seem obvious for staying visually appealing but has a much greater biological motivation. Symmetry for cnidarians like jelly fish is important for feeding and vital for propulsion or movement through the water.
Moon jellyfish are also known as the common jellyfish and for good reason. They have a wide range, often live and migrate in large groups, and are a common staple in many aquarium galleries. As one of the oldest animals on the planet alive today I think it is safe to say there is much we can learn from such resourceful and successful animals. So next time you are watching the ethereal world of a moon jellyfish (check out the video below), remember you are observing a real life Benjamin Button!