Phenotypic stasis with genetic divergence

Abstract

1AbstractWhether or not genetic divergence on the short-term of tens to hundreds of generations is compatible with phenotypic stasis remains a relatively unexplored problem. We evolved predominantly outcrossing, genetically diverse populations of the nematode Caenorhabditis elegans under a constant and homogeneous environment for 240 generations, and followed individual locomotion behavior. We find that although founders of lab populations show highly diverse locomotion behavior, during lab evolution the component traits of locomotion behavior – defined as the transition rates in activity and direction – did not show divergence from the ancestral population. In contrast, the genetic (co)variance structure of transition rates showed marked divergence from the ancestral state and differentiation among replicate populations during the final 100 generations and after most adaptation had been achieved. We observe that genetic differentiation is a transient pattern during the loss of genetic variance along phenotypic dimensions under drift during the last 100 generations of lab evolution. However, loss of genetic variances present in the founders may be due to directional selection. These results suggest that once adaptation has occurred, and on the short-term of tens of generations, stasis of locomotion behaviour is repeatable because of effective stabilizing selection at a large phenotypic scale, while the genetic structuring of component traits is contingent upon drift history at a local phenotypic scale.