This Monterey Bay deep-sea creature is the ‘sister’ that took its own evolutionary path

Northern California researchers’ genetic analysis anoints mysterious comb jelly in scientific debate

We don’t know what the first animal looked like, but scientists believe it arose 700 million years ago from a soup of single-celled organisms floating in the ocean. The multicellular creature thrived, multiplied, and evolved, eventually separating into two distinct species.

One species continued to evolve, eventually producing almost all of the animals on Earth — dinosaurs, humans, cats, and mosquitoes. The other species, the “sister to all other animals,” followed a different, more limited evolutionary path.

Scientists now have the clearest evidence to date as to which animal alive today is the sister’s true descendant: it’s the mysterious comb jelly, several species of which thrive in Monterey Bay.

After a team of Northern California researchers led by Darrin Schultz, a 30-year-old biologist at the Monterey Bay Aquarium Research Institute, published the evidence in the scientific journal Nature in May, the scientific consensus sided with the gelatinous deep-sea creature over the other leading contender, the simple sponge. The scientific community has embraced both the team’s findings and its novel approach in the months since the report was published, with many scientists now predicting that the team’s work will change the way evolution is studied.

“It’s an extraordinary result,” said Max Telford, a zoologist at University College London who has spent years researching the subject and always thought the sponge was the sister. “The new analyses are plain to see for anyone to see.”

Previously, scientists on both sides of the debate relied heavily on the traditional method of comparing individual genes in animals, but the NorCal team discovered a way to compare their entire chromosomes.

![Biologist Darrin Schultz recently led a groundbreaking study that many scientists believe will change the way scientists study evolution. Schultz, a former UC Santa Cruz Ph.D. student and researcher at the Monterey Bay Aquarium Research Institute, has accepted a postdoctoral fellowship at the University of Vienna in Austria.

The team, which included scientists from MBARI in Moss Landing, UC Santa Cruz, UC Berkeley, and the San Francisco-based Chan Zuckerberg Initiative, discovered that patterns in sponge chromosomes matched those found in virtually all other animals’ chromosomes. However, the patterns in comb jelly chromosomes were noticeably different.

“I think it really is a rewrite-the-textbook kind of moment,” said Steven Haddock, an MBARI marine biologist and adjunct professor of ecology and evolutionary biology at UC Santa Cruz. Haddock collaborated on the study with Schultz, whom he met at UCSC while Schultz was pursuing his Ph.D. in biomolecular engineering and bioinformatics.

“OK, finally I’m convinced,” Haddock said of researchers who thought the sponge was the sister species. They reluctantly admit that this is a completely new perspective.”

Because the animals are so simple, many scientists supported the sponge theory. Their bodies are essentially just tubes.

Comb jellies, on the other hand, are intricate, with eight rows of hair-like cilia that aid in their movement through the ocean. The cilia reflect light, giving the animals the appearance of floating deep-sea marquees. Comb jellies, unlike sponges, have nerve and muscle cells.

Schultz’s team made international headlines in 2021 when it published the complete genetic code of the 13 chromosomes of the California sea gooseberry, an oval-shaped comb jelly that lurks in the depths of Monterey Bay.

That research paved the way for the new study, but it was often difficult work.

Comb jellies are transparent and mostly composed of water, and they can be found up to six miles beneath the ocean’s surface. Finding and capturing them with scuba gear is extremely difficult.

Fortunately, MBARI’s remotely operated vehicle (ROV), named Doc Ricketts in honor of marine biologist Ed Ricketts, who inspired the character “Doc” in John Steinbeck’s “Cannery Row,” was on hand to assist Schultz’s team. The ROV has cameras and robotic arms for finding and collecting samples and can dive down 2.5 miles.

According to Schultz, the work was only possible because ROV and DNA sequencing technologies advanced at the appropriate time. “The ability to go down and collect a rare organism from the deep sea, take that one small animal and make a perfect genome from it… is just a really cool technological synergy that helped us achieve this,” he explained.

Schultz’s team continued collecting and sequencing other unique sea creatures from Monterey Bay, comparing their chromosomes, and making their ground-breaking discovery after unraveling the genetic code of the California sea gooseberry.

The audience was visibly stunned when Schultz first presented the team’s preliminary findings in June 2022 at an evolutionary biology conference in Roscoff, France.

“People were freaking out,” Haddock remarked. “They exclaimed, ‘Finally!'”

Telford, a zoologist based in London, and other researchers believe that a new suite of software programs developed by Schultz and shared with the world will open up new avenues for scientists who have dedicated their lives to studying evolution.

The tools, according to Anthony Redmond, an evolutionary geneticist at Trinity College Dublin whose own research pointed to the sponge, will allow scientists to track species’ evolutionary trajectories in ways “we haven’t been able to do up to now.”

Meanwhile, Schultz has accepted a postdoctoral position at the University of Vienna, where he plans to use the new techniques to “re-create the history of animal genome evolution.”

Schultz hopes that one day he will be able to see what life was like hundreds of thousands of years ago — and perhaps even discover what Earth’s first animal looked like and how it came to be.

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