Local Comb Jelly Is Our Closest Ancient Relative

Jan 6, 2014

Scientists long thought that sponges were our most distant animal relative. But a recent study presents evidence that the comb jelly is our closest ancient relative.

Credit NOAA Photo Gallery / Wikimedia Commons

If you’ve sailed Narragansett waters, then there’s a good chance you’ve gotten a glimpse of these shapeless blobs. They reflect rainbow-like iridescent colors in the water.

This gelatinous animal is covered in cilia, the little hair-like structures that also coat our lungs and intestines; the comb jelly uses it to swim and propel itself through the water.

“And as it does that, the light refracts through these cilia comb rows and it looks like rainbow light shooting up and down,” said Casey Dunn, assistant professor of ecology and evolutionary biology at Brown University. “It really looks like a spaceship right out of a sci-fi movie.”

Now scientists have enough evidence to show that comb jellies, with sophisticated nervous and muscle systems, were the first ones to split off from the animal tree. Dunn co-authored the study with this finding.

“We’re obviously interested in finding life on other planets and things, in part to see how complex structures would independently arise,” said Dunn. “It may turn out that comb jellies, right under our nose this whole time, represent one of these independent evolutions of some very complex structures.”

Dunn said much of what we know about human biology comes from studying other animals, such as mice and fruit flies.

“There has been a lot of interest in how exactly these animals are all related, because it has some important implications for the evolutionary history of animals,” said Dunn. “And it’s really important for helping us transfer our knowledge from one group of organisms to another.”

Within the past few years, Dunn said it’s become cost effective to sequence animal genomes. He said scientists are strategic about which animals to select from the tree of life in order to get a really broad sampling.

“And so, it’s these technological advances that are enabling this kind of work,” said Dunn.

Dunn and his colleagues were also surprised to find that the nervous system of the comb jellies behave differently than the nervous systems of other studied animals.  

“It turns out they don’t have many of the genes that we previously thought of as being necessary for the nervous system to function,” said Dunn. “So they are able to do a lot of the things that other animals with complex nervous systems can do, but without a lot of the genes that we always thought were necessary. So that means, not only is there this interesting evolutionary story, but there is also this interesting functional story.”