Evolution of increased variability in turning bias and correlated changes in Drosophila melanogaster

Drosophila melanogaster individuals exhibit variability in several behaviors, including in the decision to turn left or right in a two-choice assay. While being a left-vs-right biased individual is not heritable, the variability in this turning bias is, and can be a target of artificial selection in the lab. Over 21 generations of selection with a synthetic outbred population, we found that behavioral variability increases in response to selection pressure, and remains high after 3 generations of relaxation of selection. We also examined the genetic architecture of evolved variability via diallel crosses, and quantified changes in other behaviors such as activity and courtship. This experiment provides empirical proof that selection can act on the variance of behaviors in a population, without affecting the mean trait, and highlights the importance of individual behavioral variability and its genetic control.