Strong segregation promotes self-destructive cooperation

Abstract

Self-destructive cooperator (SDC), where individuals sacrifice themselves for others, poses significant personal costs yet is widespread in nature. Traditional group selection theory struggles to explain its persistence, as the extreme cost of self-destruction typically exceeds the benefit to these individuals. Here, we predict that this behavior can endure in structured environments with strong segregation, where populations are divided into homogenous groups originating from one or two founding members. In such contexts, the benefits derived from SDC are primarily confined within the homogenous SDC groups, thus preserving the value of this altruistic sacrifice and ensuring its maintenance. To validate our hypothesis, we employ a synthetic system with engineered bacteria to mimic both SDC and non-sacrificing cheaters. We then conduct automated experiments facilitated by biofoundry technology to monitor and operate the subgroups with diverse growth behaviors stemming from a restricted number of initial cells because of strong segregation. Eventually, we demonstrate that SDC indeed maintains under strong segregation, and high stress benefits SDC because it reduces the benefits received by cheaters in heterogenous subgroups. This study extends the group selection theory to encompass even the most extreme manifestations of altruism and highlights the potential of automation in evolutionary research.