Abstract
<jats:p>The evolutionary transition from free-living bacteria to mutualistic symbionts remains a central question in symbiosis research. Traditionally, this process has been inferred from comparative analyses of extant symbiotic systems, which provide evolutionary snapshots but offer limited insight into the processes connecting them. Recent studies of the stinkbug Plautia stali and its bacterial associates have begun to address this gap by integrating comparative analyses of natural systems, experimental evolution, and symbiosis engineering. Natural systems generate hypotheses about possible evolutionary trajectories, experimental evolution reconstructs the emergence of mutualistic traits and symbiont replacement, and synthetic approaches identify the biological changes that are sufficient to confer host benefits. Together, these complementary approaches suggest that mutualism can, in some cases, arise through relatively minor modifications of existing regulatory and metabolic networks and establish a new empirical framework for investigating the origins, dynamics, and evolution of insect-bacterial mutualism.</jats:p>