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.
One aspect of turtle evolution that is progressing rapidly, however, is the threat of extinction. More than half of the 330 turtle species worldwide are considered threatened, making them the most endangered major group of vertebrates. Their demise is largely due to humans, partly the result
|Contact: Alison Hewitt|
University of California - Los Angeles