Studies from biologists have found that a simple interaction between just two genes determines the patterns of fur coloration that camouflage mice against their background, protecting them from many predators. The work marks one of the few instances in which specific genetic changes have been linked to an organism's ability to survive in the wild.
What does the research show?
The work shows how changes in just a few genes can greatly alter an organism's appearance. It also illuminates the pathway by which these two genes interact to produce distinctive coloration. The result is that now there's reason to believe this simple pathway may be evolutionarily conserved across mammals that display lighter bellies and darker backs, from mice to tuxedo cats to German Shepherds.
What was studied?
Researchers studied Peromyscus, a mouse that is the most widespread mammal in North America. Within the last several thousand years, these mice have migrated from mainland Florida to barrier islands and dunes along the Atlantic and Gulf coasts, where they now live on white sand beaches. In the process, the beach mice's coats have become markedly lighter than that of their mainland brethren.
What did the research show?
Nature provides a tremendous amount of variation in color patterns among organisms, ranging from leopard spots to zebra stripes; these patterns help individuals survive. But it has been difficult to understand how these adaptive color patterns are generated. The research helped identify the genetic changes producing a simple color pattern that helps camouflage mice inhabiting the sandy dunes of Florida's Gulf and Atlantic coasts. These 'beach mice' have evolved a lighter pigmentation than their mainland relatives, a coloration that helps camouflage them from predators that include owls, herons, and hawks.
Previous research has shown that such predators, all of which hunt by sight, will preferentially catch darker mice on the white sand beaches, providing a powerful opportunity for natural selection to evolve increased camouflage.
Which Genes were involved?
Through a detailed genomic analysis, researchers identified two pigmentation genes, for the melanocortin-1 receptor (Mc1r) and an agouti signaling protein (Agouti) that binds to this receptor and turns it off. Conclusion: A single amino-acid mutation in Mc1r gene can weaken the receptor's activity, or a mutation in the Agouti gene can increase the amount of protein present without changing the protein's sequence, also reducing Mc1r activity and yielding lighter pigmentation.
What do the genes do? Both genes affect the type and amount of melanin in individual hairs. If both genes are turned on, the mouse is dark in color. If a mutation occurs, which changes either gene this leads to a somewhat blonder mouse, but when the combination of mutations occur in both genes this produces a mouse very light in color.