Anemone reveals complex past

Animals evolved complex genomes surprisingly early, new research shows. The recently completed genome of the starlet sea anemone, a primitive animal that last shared an ancestor with humans and other vertebrates about 700 million years ago, has a greater number of genes in a more complex arrangement than scientists had expected.

NOT SO PRIMITIVE. The starlet sea anemone has an unexpectedly complex genome. Srivastava, R. Howson/CIG, Univ. of Calif., Berkeley

“The assumption was that the more complex an animal you are, the more complex your genome must be,” says study coauthor Mansi Srivastava of the University of California, Berkeley. People have about 20,000 genes, while fruit flies, a relatively primitive animal widely used for genetics research, have only about 14,000 genes. Srivastava’s team expected the starlet sea anemone, which belongs to an even more primitive group of animals that includes jellyfish, to have still fewer genes. But when they sequenced its genome, the scientists found that it contains roughly 18,000 genes, they report in the July 6 Science.

The anemone genome also contains many segments of noncoding DNA that must be delicately spliced out of genes when they are transcribed to RNA. The study suggests that this sophisticated genetic feature—one that scientists thought occurred primarily in higher animals—was present even in the ancient common ancestor of people and anemones.

“It challenges our ideas about what it means to be a complex organism,” Srivastava says.