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Selecting Against Nature Solves a Century-old Mystery

10/13/2015
Nicholas Miliaras, PhD

The relative sizes and shapes of many body structures are highly conserved and directly linked to physiology and behavior. What happens when researchers change these ratios? Find out...


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.

“In the fly wing there is a relationship between roundness and size, so that smaller wings are rounder than larger wings. This relationship is highly consistent both across individuals of the same species and across different species,” said Geir Bolstad at the Norwegian University of Science and Technology.

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.”

Reference

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.

Keywords:  evolution