That's why it's exciting-we can make the link all the way from genotype to phenotype,' Nachman said. 'This is a study where we really have all the pieces of the puzzle in one place. This perfect association between the genetics and the coat color makes it almost certain that the dark color in the Pinacate mice is caused by the changes in their Mc1r gene, according to Nachman. Two light mice collected on the dark rocks used the 'light spelling' for their Mc1r genes, and the lone dark mouse found on the adjacent light rocks used the 'dark' spelling.

All 18 dark-colored Pinacate mice shared a common set of 4 single-letter spelling differences in their Mc1r gene compared to the light-colored mice collected nearby. The Pinacate mice showed a perfect match between coat color and spelling of their Mc1r gene. Light and dark rock pocket mice on light granite and dark basalt rocks In addition to sampling the dark mice captured on the basaltic areas, they sampled light mice captured on light rocks just adjacent to the sites.

They knew the DNA sequences of the lab mouse versions of these genes, which helped them to find and read the genes from their rock pocket mouse specimens. Nachman's group made an educated guess that genetic differences in either the Mc1r or agouti genes might account for the dark pelage of rock pocket mice living in the volcanic areas. Another, called agouti, controls lighter yellow and reddish pigmentation. One gene, called Mc1r, stimulates production of the black pigment in coat fibers. Some of the genes exert more influence on the color palette than others, which fine-tune the hues and patterns. Scores of different genes control fur pigmentation, and thanks to modern genomic technology, they've all been identified at the DNA sequence level for lab mice. Biologists have worked out in fine detail the genetic and biochemical processes that control mammalian coat color, particularly for the common lab mouse, an evolutionary cousin of rock pocket mice. 'But even after more than 50 years of intensive study,' Nachman said, 'we still don't know which genes are involved.' In fact, he added, 'there are very few examples where we actually know the genes that underlie an adaptation in nature, and almost no examples for cases of natural selection that are not induced by human disturbances,' such as pesticide or heavy metal resistance. Peppered moths make a compelling case study in natural selection. A classic illustration of 'survival of the fittest.' As the cities reduced the pollution, the tree trunks lightened up, and so did the moths. Eventually, black became the norm for urban peppered moths. Better camouflaged than their light-colored brethren, the dark forms survived and proliferated.

In a short time, though, dark variants of the moths sprang up. Coal soot from burgeoning industry gradually blackened tree trunks in urban areas, and left the moths more vulnerable to predators. In pre-industrial England, most peppered moths had mottled grey wings, camouflaging well with the birch trees upon which they rested. The story is reminiscent of the peppered moth lesson from high school biology class. Almost all of the mice collected from the volcanic formations had dark coats-the better to stay concealed from hungry owls, which can pick off mice from contrasting backgrounds even at night. Nachman's group collected pocket mice from two of these black rock islands-the Pinacate formation in southwestern Arizona and the Pedro Armendaris formation of New Mexico. But scattered throughout the southwest are islands of black basaltic rock formed from not-so-ancient lava flows. Most of the mice have light tawny fur, which blends in well with the desert granite substrates they typically inhabit. Nachman, examined the coat colors of rock pocket mice. The group, led by Professor of ecology and evolutionary biology Michael W.

Two variates of rock pocket mouse