Biologists at the University of California, San Diego have found that the main color differences among Florida's mice--which are darker on the mainland, but lighter on the barrier islands to blend in with the white sand dunes--are largely due to a simple genetic mutation.
Their discovery, detailed in the July 7 issue of the journal Science, is one of the first to demonstrate how a small change in a single nucleotide--the smallest subunit of a gene--can affect the survival and evolutionary fitness of an organism in the wild.
Because the mice differ not only in overall color, but in pigmentation pattern, the study also provides geneticists with a first step toward understanding how color patterns, such as zebra stripes and leopard spots, are generated in animals. And it raises the possibility that other vertebrates, such as mammoths, also evolved similar color variations using the same genetic mutation.
In a companion paper published in the same issue of Science, researchers in Germany report the discovery of this same mutation within DNA extracted from a 43,000-year-old bone of a wooly mammoth preserved in the permafrost of Siberia. Because the variations occur in the same nucleotide used by the Florida beach mice to alter their coat color, the University of Leipzig scientists say, populations of mammoths during the last Ice Age were likely composed of dark- and light-coated individuals.
"While there is growing evidence that phenotypic differences between organisms, like humans and chimps, are largely controlled by changes in gene regulation, these two studies are striking examples of how amino acid changes in structural proteins can also be important," says Hopi Hoekstra, an assistant professor of biology at UC San Diego who headed the team that discovered the genetic roots of the color differences in Florida's mice.