13.6.6 Evidence for the resource allocation model

Even though this is a simple model, the directions of selection response do occur in reality. To illustrate that, in figure 7 you see the results of a selection experiment in mice. A population of mice was divided in two and kept on two different diets with respect to protein content for 6 generations. Then they were put in the opposite environment and their growth performance was measured. Both sub-populations performed best in their own environment. However, the group that was selected on the high protein diet suffered much more in the other environment than the group that was selected on the low protein diet. The results are presented as reaction norms in the figure below. The fact that they are non-parallel, and even crossing, shows that genotype by environment interaction can be created in only a limited number of generations. Populations, or breeds, adjust to their environment.

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Figure 7: A population of mice was divided into two and bred on two diets with different protein level. In generation 7 their performance was recorded on both diets. Each population performed best on their own diet.