The Adelie penguins of Antarctica can give insight into mechanisms of evolution. Credit: background photograph Yvette Wharton, artwork Vivian Ward.
Analysis of DNA from the remains of 6,000-year old Adelie penguins in Antarctica has allowed researchers to observe natural microevolutionary changes—changes at or below the species level—for the first time.
In the study, published in the November 15th issue of the Proceedings of the National Academy of Sciences, scientists compared the DNA of penguin subfossils (they're not old enough to be called "fossils") to modern penguin DNA, and made a surprising conclusion: The primary mechanism that spurred the evolution of Adelie penguins over the last 6,000 years was environmental effects rather than natural selection.
"The person on the street would think of evolution as being something that's precipitated by natural selection," said David Lambert, a professor from Massey University in New Zealand, and coauthor of the study. "But, in fact, we have very good reason for believing that this had nothing to do with natural selection, and it actually had to do with this physical component of the environment and the effects it had on the movement of individuals. And that movement of individuals resulted in evolution."
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Adelie penguins are free to migrate, but they typically return to their birthplaces to breed. This makes them ideal for studying the changes in gene frequency over both time and geographical distance. In addition, the cold, arid Antarctic climate preserves penguin remains, which allowed the researchers access to older DNA.
An analysis of several generations of penguin remains found that DNA sequences that were common 6,000 years ago are virtually gone today, and that newer sequences are now quite common. Less extreme changes in frequency for non-protein-coding DNA sequences gave researchers confidence that natural selection pressures did not play a role in the microevolution of the penguins.
The researchers believe that the biggest factors affecting the evolution of penguins are mega-icebergs. They argue that the cyclical formation of giant icebergs disrupts the migration patterns of the penguins and that this environmental change acted faster to spur penguin evolution than natural selection.
The researchers are now taking a closer look at the high mutation rates in today's penguins. The comparison will show whether or not evolutionary processes are actually occurring much faster than expected in the Adelies.
"That would lead you to wonder whether other organisms—humans included—over that 6,000 year period would have changed in a similar kind of way," said Lambert.