What surprised Hoekstra and her team, however, wasn't that the gene was involved, but that each of the nine mutations were tied to a unique change in the animal's coats, that all the new mutations led to more camouflaging color, and that the mutations occurred in a relatively short, 8,000-year timeframe.
"Essentially, it seems as though these mutations each of which makes the mouse a little lighter and more camouflaged have accumulated over time," Hoekstra said.
Focusing on these mutations, researchers then examined the DNA of natural populations of the mice to determine whether the mutations are actually beneficial.
"For each of the mutations associated with color change, we also find a signal that's consistent with positive selection," Hoekstra said. "That implies that each of the specific changes to pigmentation is beneficial. This is consistent with the story we are telling about how these mutations are fine-tuning this trait."
While the findings offer valuable insight into the way natural selection operates, Hoekstra said they also highlight the importance of following research questions to their ultimate end.
"The question has always been whether evolution is dominated by these big leaps or smaller steps," she said. "When we first implicated the agouti gene, we could have stopped there and concluded that evolution takes these big steps as only one major gene was involved, but that would have been wrong. When we looked more closely, within this gene, we found that even within this single locus, there are, in fact, many small steps."
Going forward, Hoekstra said, her team hopes to understand the order in which the mutations happened, which would allow them to reconstruct how the mice changed over time.
"For evolutionary biologists, this is exciting because we want to learn about the
|Contact: Peter Reuell|