Painted Turtle Genome Mapped, Yields Surprises, Supports Archosaur Affinities

UCLA conservation biologist and lead author Brad Shaffer collaborated with the Genome Institute at Washington University in St. Louis and 58 co-authors on the multi-year research project. Their paper, which appears in the journal Genome Biology, describes the genome of the western painted turtle, one of the most widespread and well-studied turtles in the world.

Researchers were somewhat surprised to find that the painted turtle's extraordinary adaptations were not the result of previously unknown genes but of gene networks that are common in vertebrates — including humans, said Shaffer, a professor at UCLA's Institute of the Environment and Sustainability (IoES) and UCLA's Department of Ecology and Evolutionary Biology.

"They're the same genes we have, and the turtles are just using them in different ways and really cranking up their activity in most cases," said Shaffer, who also directs the La Kretz Center for California Conservation Science at the IoES.

"Given how extreme their adaptations are, I imagined we would see weird new genes, so I was surprised," he added. "But the fact that they're common means they may have direct relevance to human health conditions, especially those related to oxygen deprivation, hypothermia and possibly longevity."

Inside the turtle genome, the researchers found 19 genes in the brain and 23 in the heart that became more active in low-oxygen conditions, including one that became 130 times more active. These genes, all of which are present in humans, may be important candidates for exploring oxygen-deprivation treatment in humans, the researchers noted.

Many of the extreme adaptations the researchers studied, such as the ability to survive months of anoxia — total oxygen depletion — are primarily seen in painted turtles, and the western painted turtle is the most anoxia-tolerant terrestrial vertebrate known. At low temperatures, such as in the ice-covered ponds where they hibernate, painted turtles can survive for four months underwater without coming up for air. Turtles are also famous for their extreme longevity, with some species even continuing to reproduce into their second century of life.

But when the research team examined genes that may be responsible for turtles' longevity, instead of finding super-active genes like the ones protecting them from oxygen deprivation, the scientists found indications that turtles' long life spans may come from silencing "life-shortening" genes.

"We looked at two genes that are either absent or severely down-regulated in other animals that live a long time," Shaffer said. "We found turtles have only non-functioning vestiges of these genes, if they have them at all. Both of these genes are present and active in humans, so they're an appealing candidate to learn about human longevity."

Analysis of the turtle genome confirmed that the shelled creatures are more closely related to birds and crocodilians than any other vertebrates. The researchers also discovered that turtles have an extraordinarily slow rate of genomic evolution and that the turtle genome evolves at about a third the rate of the human genome.

Awesome and bummer at the same time.  I was hoping the turtles were the last of the parareptiles.  Alas.