What would you do if you could live forever? Would you climb every mountain? Read every book? Formulate plans for world domination? Embarrassingly, our greatest scientific minds have been beaten to the punch by a tiny little jellyfish, measuring no more than five millimeters across.
Turritopsis dohrnii (T. dohrnii), originally known as Turritopsis nutricula resembles a tiny, translucent bubble with many tentacles. Different specimens have been found with anywhere between eight and 24 tentacles, though genetic tests have shown that they are in fact the same species.
T. dohrnii floats through the ocean like any other jellyfish, but when most jellies would die at the end of their life cycles, T. dohrnii transforms into a tiny blob, anchors itself to a rock or other surface, and changes back into its juvenile, polyp form.
This form of reverse metamorphosis is called transdifferentiation – when one cell turns into a different kind of cell. A few other animals experience this in limited forms. For example, salamanders and starfish can re-grow limbs. However, T. dohrnii is the only known animal that can regenerate its entire body. It is believed that this process can continue perpetually, and the jelly’s ability to do so has earned it the nickname, “immortal jellyfish.”
“Lots of jellies have a similar life cycle,” said Rick Grosberg, a professor of evolution and ecology, and head of the Grosberg Lab at UC Davis.
“In the attached polyp phase, we have no idea how old they are. They have the potential to be immortal,” Grosberg said.
The polyps attached to rocks or docks start off as one individual, and grow to be tens of thousands to hundreds of thousands of individuals. The polyps then go through a process called strobilation, where they slice themselves up until they resemble a stack of saucers. The oldest “slice” breaks off and forms a new male or female jellyfish.
Male and female jellies spawn sperm and eggs, respectively, into the water. The fertilized egg becomes a little wormlike creature called a planula.
“The planula, if lucky, finds a place and attaches, and starts making new polyps,” Grosberg said.
Since the jelly never dies of old age, it has the potential to keep reproducing for many generations until it is either eaten or killed off some other way. These low death rates and very high birth rates have put Turritopsis dohrnii well on the way to a worldwide oceanic presence.
“Jellies that have a polyp stage will begin to compete with corals for space, or any invertebrate,” said John Stachowicz, an evolution and ecology professor at Davis.
T. dohrnii is not the only jelly that is rapidly filling the oceans. In many polluted areas of the ocean where oxygen is too scarce for other organisms to function, jellies seem to thrive. A report from the National Science Foundation claimed that in the densest swarms, there could be “more than 1,000 fist-sized jellies per cubic meter.”
In the oxygen-deprived environment that Grosberg described, photosynthesizing corals would not be able to compete with jelly polyps.
Marine biologists continue to be curious about jellyfish. For those of you who have class in the Sciences Laboratory Building, you may have seen the jellyfish display tank full of Moon Jellies.
“It is very hard to display and show soft bodied animals,” said Thien Mai, the laboratory supervisor and safety coordinator for the lab buildings.
“The display is meant to provide live, soft bodied organisms for study,” Mai said.
These gelatinous beauties are some of the most fascinating creatures in the sea. More is learned about them all the time, and maybe, one day we will figure out how a little jelly defeated death.
HUDSON LOFCHIE can be reached at firstname.lastname@example.org.