Causes and consequences of imperfect coordination in microbial collective behaviors

Collective behaviors, in which many individuals exhibit some degree of behavioral coordination, are frequent across the tree of life and observed across a continuum of scales, from microbial aggregates to ungulate migrations. Intriguingly, however, such coordination is sometimes imperfect, and “out-of-sync” individuals have been reported in several of these systems. For example, in the model social amoeba Dictyostelium discoideum, free-living cells aggregate in a multicellular fruiting body upon starvation, while others remain in the unicellular phase. In several ungulate species, hundreds of thousands of individuals coordinate with each other to migrate across seasonal ranges, but resident populations that fail to migrate also exist. The roots of such imperfect coordination, and hence the mechanisms underlying the emergence of out-of-sync individuals, will undoubtedly differ across systems. Nevertheless, the occurrence of imperfect coordination across such different systems and scales raises fundamental questions about its causes and consequences. Are “out-of-sync” individuals merely inevitable byproducts of large-scale coordination attempts, or can they, at least in some systems, be a variable trait that selection can shape with potential ecological consequences?