Owls have a name for a white mouse on a black rock: "dinner."
Scientific studies (not to mention simple logic) have shown that mice whose coloration doesn't match their surroundings are easier prey, not only for owls but for coyotes and other sharp-eyed predators.
So when the straw-colored pocket mouse found itself living in a landscape blackened by volcanic eruptions, it evolved into a black mouse.
Michael Nachman knows exactly how that happened.
Nachman, the third speaker in the "Genomics Now" series of the University of Arizona College of Science, will talk Wednesday about how the ability to sequence the entire DNA of organisms has made it possible to complete our knowledge of how evolution occurs.
Charles Darwin, more than 150 years ago, figured out the process of evolution by meticulously observing the natural world.
He didn't know about the genetic mutations that allowed it to happen, nor could he have envisioned a future when information about the entire genomes of living things would become readily available.
Nachman and his graduate students in the UA Department of Ecology and Evolutionary Biology found a perfect demonstration of Darwin's theory of natural selection in the mouse populations that live on dark-colored lava flows in three areas, including part of the Pinacate formation that extends from Sonora into Southwestern Arizona.
While recent advances in genomics provided the answers, the researchers wouldn't have known the questions, but for the evolutionary foundation established by Darwin, said Nachman. "Evolution has really helped us understand the genome," he said.
Darwin, for instance, could have figured out the process by which white mice turned into black ones.
Melanism, or pigment darkening, is a mutation that occurs occasionally in mammals. Black panthers and jaguars reoccur amid a population of mostly spotted cats.
If melanism gives a creature a competitive advantage - if, for example, more black mice survive to breed - their numbers increase.
Ultimately, the dark-haired mice predominate. The shorter the breeding season, the faster the change occurs. With pocket mice, which produce large litters twice a year, it can occur very quickly.
The field observations of Nachman and his students led them to the places in the creature's genome they already knew had something to do with melanism.
They identified the particular gene and the particular chemical process that caused the evolutionary change.
Nachman continues to lead research into genetic changes in mice, including a current study that looks at adaptation that helps mice survive in colder climates, where they put on extra layers of fat. Such studies could provide clues to the causes of human obesity.
Nachman also promises to answer questions about how new species evolve and why humans are no more genetically complex than worms. "Genetics," he said, "has absolutely transformed our understanding of evolution."
IF YOU GO
• What: "Genomics Now," UA College of Science lecture series
• When: 7 p.m. Wednesdays, Jan. 30 to March 6
• Where: Centennial Hall, 1020 W. University Blvd.
• Cost: Free
• Parking: Tyndall Avenue Garage is most convenient. A fee is charged. Note: The intersection of North Park Avenue and East University Boulevard is closed for streetcar construction. Take North Euclid Avenue to the East Fourth Street entrance to the garage.
• Information: 520-621-4090 or cos.arizona.edu/connections/genomics-now
"Genomics and the Complexity of Life" - Michael W. Nachman, professor of ecology and evolutionary biology.
"The 9 Billion-People Question" - Rod A. Wing, Bud Antle Endowed Chair, School of Plant Sciences, director of the Arizona Genomics Institute.
"Epigenetics: Why DNA Is Not Our Destiny" - Donata Vercelli, M.D.; professor of cellular and molecular medicine; director of the Arizona Center for the Biology of Complex Diseases.
Genomics Tomorrow - A discussion of mankind's role and responsibilities in choosing to "modify" nature, moderated by UA Dean of Science Joaquin Ruiz.
Contact reporter Tom Beal at email@example.com or 573-4158