With a thousand mice born every generation and four generations of mice each year, the researchers were able to breed highly active mice in the four high-runner lines by selecting the highest running males and females from every generation to be the parents of the next generation. In the control lines, breeders were chosen with no selection imposed, meaning that the mice either changed or did not change over time purely as a result of random genetic drift.
By studying the differences among the replicate lines, the researchers found that mice in the four high-runner lines ran 2.5-3-fold more revolutions per day as compared with mice in the four control lines. They also found that female and male mice evolved differently: females increased their daily running distance almost entirely by speed; males, on the other hand, increased speed but they also ran more minutes per day.
Theodore Garland Jr., a professor of biology at the University of California-Riverside, describes findings from his lab showing that voluntary activity, such as daily exercise, is a highly heritable trait that can be passed down genetically to successive generations. Credit: UCR Strategic Communications
The study is an example of an "experimental evolution" approach applied rigorously to a problem of biomedical relevance. Although this approach is common with microbial systems and fruit flies, it has rarely been applied to vertebrates due to their longer generation times and greater costs of maintenance. The results of such studies can inform biologists about fundamental evolutionary processes as well as "how organisms work" in a way that may lead to new therapeutic strategies.
"This study of experimental evolution confirms some previous observations and raises new questions," said Douglas Futuyma, a distinguished professor of ecology and evolution at Stony Brook University, New York, who was not involved in the research. "It shows that 'there are many ways to skin a cat': different ways in which a species may evolve a similar adaptive characteristic – running activity, in this case. Garland and coauthors go further by beginning to explore the detailed ways in which an adaptive feature, such as muscle size or metabolic rate, may be realized and by showing sex differences in the response to selection. It would be fascinating to know, and challenging to find out, if any one of these different responses is adaptively better than others."
Theodore Garland Jr. is a professor of biology at the University of California, Riverside.
(Photo Credit: UCR Strategic Communications.)