Point of View: Is cell size a spandrel?
Figures
![](https://iiif.elifesciences.org/lax/22186%2Felife-22186-fig1-v1.tif/full/617,/0/default.jpg)
Phenomenological models for cell size control in bacteria.
This graph shows how the size at division, , depends on the size at birth (x-axis) in three different models. The parameter is related to the slope of the function, and can continuously interpolate across different models. Its value can be determined from single-cell level correlations (Amir, 2014; see Marantan and Amir, 2016 for a recent generalization of this phase diagram). As increases from 0 to 1, the correlations between mother and daughter cell sizes become weaker, yet the size distribution becomes narrower. The prevailing model for a critical size at initiation is effectively a ‘sizer’, and is inconsistent with recent experimental data supporting an ‘adder’.
![](https://iiif.elifesciences.org/lax/22186%2Felife-22186-fig2-v1.tif/full/617,/0/default.jpg)
Bacterial evolution and growth regulation.
E. coli cells evolving in a culture tube show both increasing fitness over time as well as increasing size. This can be naturally explained by a simple, specific regulation strategy, consistent with additional experiments. Figure adapted from Lenski and Travisano, 1994, with permission.