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.
Camouflaged beach mouse forages on the coastal sand dunes in Florida. Credit: Robert Burks
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.
The coat pattern and color differences among populations of mice on the mainland and the barrier islands off the Florida Gulf and Atlantic coasts have been studied extensively since the 1920s, first by Francis Sumner of UCSD’s Scripps Institution of Oceanography. Sumner used the mice as a textbook example of how small, geographically isolated populations could adapt to their new environments and diverge into distinct subspecies.
Known to scientists as Peromyscus polionotus, mice living on the mainland have dark coats, which help them blend in with the vegetation and avoid their main predators—owls, hawks and herons—that hunt prey by sight. But on five barrier islands off the Florida Gulf coast and three off Northern Florida’s Atlantic coast, geographic isolation of the populations has resulted in eight distinct subspecies of beach mice, each with distinctive coat patterns that are lighter in color than their mainland counterpart.
“We know from geological evidence that the barrier islands are very recent, less than 6,000 years old,” says Hoekstra. “So these color mutations may have evolved rapidly.”
While scientists have been studying the genetics of complex coat patterns of these mice for nearly a century, few suspected that the simple mutation of a single nucleotide could have such a major impact on their coloration.
“We were surprised that this one gene could explain up to 36 percent of the variation we see in the mice,” she says. “It’s a large effect mutation. And what it says is that adaptation does not always occur gradually, but may happen in these relatively large jumps.”
Hoekstra and her colleagues—Rachel Hirschmann of UCSD’s Division of Biological Sciences and Richard Bundey and Paul Insel of UCSD’s Department of Pharmacology—discovered the single nucleotide mutation in the melanocortin-1 receptor, a gene which regulates the pigmentation of hair color.
In laboratory mating of the different subspecies to produce genetic crosses, the UCSD scientists report in their paper that the variations of this gene account as much as 36 percent of the color variation in Gulf Coast mice. Surprisingly, however, this mutation was absent in the two Atlantic Coast subspecies, even though these Atlantic coast beach mice have similarly light colored coats. The results suggest that beach mice gain their light coloration through different genetic mechanisms.
“There is apparently more than one way genetically to become a light-colored beach mouse,” says Hoekstra.
Other genes also contribute to the differences in the coat patterns among the mice. But, concedes Hoekstra, “We know very little genetically about how coat patterns are generated in mammals. This study is a first step toward understanding this complex genetic process.”
Unfortunately for the scientists, the subjects of their study are disappearing rapidly. One of the eight original subspecies studied by Sumner has since become extinct and six of the seven remaining subspecies are considered endangered because their habitats are being destroyed by human development.
“These mice exist on beautiful white-sand beaches, inhabit the sand dunes and feed on sea oats,” says Hoekstra. Their pristine habitat is being destroyed by human development coupled with hurricanes.
“Unfortunately these mice like the same habitat where people want to build beach homes and the two don’t coexist well together,” she adds. “The mice are now only found in protected areas, and hurricanes become a big threat because these beach mouse populations, which are so wonderfully adapted to their environment, are now small and fragmented.”
Funding for the study was provided by the National Science Foundation.Comment:
Kim McDonald | EurekAlert!
A novel socio-ecological approach helps identifying suitable wolf habitats
17.02.2017 | Universität Zürich
New, ultra-flexible probes form reliable, scar-free integration with the brain
16.02.2017 | University of Texas at Austin
In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".
Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
17.02.2017 | Medical Engineering
17.02.2017 | Medical Engineering
17.02.2017 | Health and Medicine