Abstract
Abrupt environmental changes are of particular interest to understand how species can quickly evolve at the boundary of their current niche. In particular the "sliding niche" model, wherein a niche shifts globally toward the new condition, has been used in understanding and modeling this process. Here, we investigate the dynamics of relative fitness change in four evolutionary replicates of Escherichia coli populations exposed to an extreme pH shift. We analyzed these changes at generations 500, 1000, and 2000 to determine whether niche global deformations fully capture the temporal dynamics of niche evolution. Strikingly, this analysis reveals that fitness variations can indeed be attributed to simple and global deformation of an underlying simple niche template. Analysis from two experimental replicates displays a transient increase in niche width, consistent with recent theory considering plasticity evolution in the context of an abrupt environmental change. We term this scenario the "sidestep niche model.