March 24, 2008 -- One of the world's most laid-back animals, the tuatara, may be the fastest evolving creature on Earth, according to a paper in this month's Trends in Genetics.
The lizard-like reptile's DNA changes naturally at a rate faster than has been observed in any other animal: 1.56 changes per nucleotide (DNA subunit) every million years.
The finding is particularly surprising in light of the fact that the tuatara, endemic to New Zealand, hasn't changed much physically since its ancestors hung out with dinosaurs 225 million years ago. Almost everything about the foot-long reptile is slow and easy.
Co-author David Lambert said the tuatara does all things slowly. He explained that "they grow slowly, reproduce slowly and have a very slow metabolism" when "in fact, at the DNA level, they evolve extremely quickly."
Lambert, a professor at the Allan Wilson Center for Molecular Ecology and Evolution at Massey University in New Zealand, now believes the rate of an organism's molecular evolution and the way it changes, or doesn't, over time are not necessarily connected.
"The processes that govern one are different than the processes that govern the other," he told Discovery News.
When scientists study an animal's rate of evolution, they usually compare one species to its close relatives. That was impossible for the tuatara, a "living fossil" whose close ancestors are all extinct. The reptile even looks like a mini dinosaur, with clawed feet and short spikes on its back.
For the study, Lambert and his team amplified and sequenced DNA from the bones of 33 ancient tuataras, dating from more than 8,750 years ago to 650 years ago, as well as blood samples from 41 modern individuals.
While the tuatara holds the top speed record for evolution, scientists are beginning to make a list of runners-up. In order, below the tuatara, they are as follows: Adelie penguin, auroch, Mappin's moa, bison, brown bear, cave bear, cave lion, ox and horse.
The new finding counters prior theories about what factors determine genetic evolutionary rates. For example, it was thought that animals that grew and matured quickly would have high rates. The tuatara, in contrast, can grow as old as 100 years and may only give birth after 10 to 15 years of age with offspring possible at two to five-year intervals.
It was also believed that cold-blooded animals had slow rates of evolution. The tuatara, however, is cold-blooded, and can only survive in temperatures above 77 degrees Fahrenheit.
"Many things (from the distant past) survived in New Zealand -- a survivor's paradise, I would say," Lambert explained. The tuatara is now rare and listed as vulnerable by conservationists.
Although the discovery about the tuatara's speedy evolution goes against conventional wisdom, it supports a prediction made 40 years ago by evolutionary biologist Allan Wilson of New Zealand, who supported the then-controversial notion that "the rate of molecular evolution was uncoupled from the rate of morphological [body shape] evolution."
Wilson even applied this approach to human evolution, something Lambert and his colleagues hope to investigate as well.
"We want to go on and measure the rate of molecular evolution for humans," he said. "There are human mummies in the Andies and some very good samples in Siberia where we have some collaborators."
Related Links: