What's the problem?
Examples of animals adapting to the environment have been known as far back as the case of the black peppered moths of England in the mid-1800s. In that case, entire populations of the black peppered moths were observed to change color in response to changes in their environment. More recently, bacteria have been known to develop resistance to antibiotic drugs, insects have developed various forms of resistance to insecticide, and plants have adapted to accommodate higher levels of heavy metals in the soil and water.
The problem is that it is difficult to locate the genes that stimulate adaptation for three reasons:
Traits must be identified based on how they affect fitness and their ecological relevance. In other words, we need to find a trait that clearly makes a difference in whether or not the animal survives.
It is challenging to analyze phenotypes when there is little information known about genes. With the moths, nobody knows which of the moth's genes are responsible for the changes in color, so a genetic analysis is extremely difficult to do.
Most fitness-related traits are a mixture of many genes. This makes it hard to pin down the adaptations as a result of the actions of one gene.
So where do the mice come in?
Dr. Nachman's research explores the connection between genotype and coat color in four populations of rock pocket mice. Rock pocket mice live in rocky habitats in the southwest U.S. and northern Mexico. In the 1930s, classical studies revealed that there was a close correlation between the color of a mouse's coat, and the color of the rocks the mouse lived on. Light-colored mice generally live on light-colored rocks, and dark-colored mice live on dark-colored rocks. This was believed to be the result of an adaptation to predation by owls.
Light- and dark-colored mice
Light-colored mice generally live on light-colored rocks, and dark-colored mice live on dark-colored rocks.
The ecosystem of mice and rocks presented a promising place to look for genes that can change in response to pressures exerted by the environment. The dynamics were simple: owls will eat the mice they can find, so a population of mice must adapt by living on rocks where they can blend in. The habitats were also easily marked: lava flows constitute dark rock, and the surrounding desert contains the light rock. So, it's not difficult to see how the environment can exert a pressure on the genes that control the coat color of the mice.
Finally, the genes that determine the coat color are well known from studies of humans and lab mice. In other words, the ecosystem of mice and rocks presented in this study satisfies the three requirements that make it so hard to study this sort of problem.
And we are looking for what, exactly?
The objective is to find and isolate the genes that are...