Allometry is the scaling of biological traits or processes (such as metabolism) with size in an organism. It is precise and does not change over millions of years. For more than a century, researchers have wondered if this results from natural selection for optimal function or is caused by constraints that prevent evolutionary change. Now, one team reports the answer in the journal Proceedings of the National Academy of Sciences.
With his colleague, David Houle at Florida State University, Bolstad recently examined this relationship by looking at wing allometry in 111 species of Drosophila separated by at least 50 million years. “We managed to select on this relationship, so that larger wings became rounder than smaller wings within the same population, and vice versa so that smaller wings became even rounder than large wings,” he said.
These results, obtained after 26 generations of selection, showed that change to allometric ratios was indeed possible. However, when they removed the selective pressure, the shape and size changes were lost after only 15 generations.
“[We] probably selected on genetic variants that are deleterious for other important traits affecting survival or reproduction, suggesting that allometric relationships are constrained by the underlying genetic architecture,” Bolstad explained. “We have learned that genetic constraints can play an important role in evolution.”
Bolstad, GH et al. “Complex constraints on allometry revealed by artificial selection on the wing of Drosophila melanogaster.” Proc Natl Acad Sci U S A. 2015 Sep 14. pii: 201505357.