Jellyfish may be the oldest group of animals on Earth, a recent study published in the journal Nature Ecology & Evolution reports.
This new research comes from researchers at Vanderbilt University and helps add to a decade-long debate about whether or not jellies or sponges were the first animals to evolve. In the past, most scientists believed that sponges came first because of how simple their bodies are compared to other species. However, new genetic analysis shows that the comb jelly (a ctenophore) likely appeared before them.
The debate began in 2008 when a group of scientists made a family tree that suggested comb jellies were the earliest members of the animal kingdom. Though their evidence was compelling, many researchers conducted follow-up studies with conflicting results.
To make sense of this, the team in the recent study looked at 18 controversial relationships — seven from animals, five from plants, and six from fungi — to figure out why those sections of the animal tree do not match up. They did this by comparing the individual genes of animals in the different groups.
“In these analyses, we only use genes that are shared across all organisms,” said study co-author Antonis Rokas, a professor of Biological Sciences at Vanderbilt University, in a statement. “The trick is to examine the gene sequences from different organisms to figure out who they [the sequences] identify as their closest relatives. When you look at a particular gene in an organism — let’s call it A — we ask if it is most closely related to its counterpart in organism B, or to its counterpart in organism C, and by how much.”
Researchers looked at thousands of genes in order to figure out which species had the most in common with its close relatives. The earlier a group appeared, the earlier it likely split off into a new species. This means that older groups would have more related species than later ones. Out of every single class studied, the comb jelly had more genes that support the “first-to-diverge” status than sponges, Live Science reports.
Scientists also found that in some cases one or two “strongly opinionated genes” could largely skew data results. They believe such genes were the reason it was so difficult for scientists to determine that jellyfish evolved before sponges. The removal of even a single opinionated gene can alter analysis, and the team states if researchers are more aware of them in the future, the new method could help answer many questions about animal evolution.
“We believe that our approach can help resolve many of these long-standing controversies and raise the game of phylogenetic reconstruction to a new level,” Rokas added.