An ancient reef coral turns out to have more in common with humans than anyone would have thought. The colorful cnidarians share genes with humans that are absent from fruit flies and roundworms, two well-known evolutionary intermediates. The findings upend scientists' assumption that vertebrates developed unique genes to deal with more complex body systems long after an evolutionary split from invertebrates.
Because dozens of mammalian genes have no counterparts in flies or worms, scientists thought that these particular DNA codes had made their debut in vertebrate animals. To test this hypothesis, David Miller, a geneticist at James Cook University in Queensland, Australia, and colleagues compared DNA snippets from the primordial coral, Acropora millepora, to humans, flies, and worms. To their surprise, the coral shared 11% of the 1376 stretches of DNA sampled with humans--but not with flies and worms. Conversely, only 1% of the coral genes were shared exclusively with flies and worms, Miller and colleagues report in the 16 December issue of Current Biology.
In humans, many of the genes shared with coral are involved in complex functions such as early neural development. What the coral do with their versions of these genes is a mystery. Although coral boast vibrant colors and intricate outer coatings, the creatures are only made up of a few tissue types. "I find it very surprising that such a morphologically simple organism has many of the genes that we associate with complex patterning," Miller says.
The findings suggest that many of the genes once considered unique to vertebrates weren't invented by vertebrates after all, Miller says. Genes like the ones shared by humans and coral may have gotten booted out of the fly and worm genomes as the organisms were faced with pressure to maintain a small genome, the team speculates. Indeed, other researchers have found that a streamlined genetic makeup is an advantage for fly embryos during early development.
"I think [this study is] another example of how our anthropocentric tendencies can lead us astray," says Danny Brower, a geneticist at the University of Arizona in Tucson. Scientists also have to remember, he notes, that the flies and worms favored by geneticists for lab studies have changed over time and may sometimes be deceptive.