  In contexts ranging from embryonic development to bacterial ecology, cell
populations migrate chemotactically along self-generated chemical gradients,
often forming a propagating front. Here, we theoretically show that the
stability of such chemotactic fronts to morphological perturbations is
determined by limitations in the ability of individual cells to sense and
thereby respond to the chemical gradient. Specifically, cells at bulging parts
of a front are exposed to a smaller gradient, which slows them down and
promotes stability, but they also respond more strongly to the gradient, which
speeds them up and promotes instability. We predict that this competition leads
to chemotactic fingering when sensing is limited at too low chemical
concentrations. Guided by this finding and by experimental data on E. coli
chemotaxis, we suggest that the cells' sensory machinery might have evolved to
avoid these limitations and ensure stable front propagation. Finally, as
sensing of any stimuli is necessarily limited in living and active matter in
general, the principle of sensing-induced stability may operate in other types
of directed migration such as durotaxis, electrotaxis, and phototaxis.
