Community mixing selects for predation resistance in lab-evolved communities of bacterial prey and social predatorMyxococcus xanthus

Abstract

AbstractAll forms of social interactions are strongly affected by population mixing and modes of transmission. However, largely because of the unavailability of an easily tractable model system, the effect of repeated community mixing on the evolutionary dynamics of microbial predator-prey interactions remains largely unexplored1. Hence, in a laboratory evolution experiment, we propagated bacterial predator-prey communities in two distinct transfer regimens. In the first regimen predator-prey communities were repeatedly mixed (horizontal transfer), and in the second treatment communities were not mixed (vertical transfer). To do so, we usedMyxococcus xanthusas a generalist bacterial predator andEscherichia colias a prey bacterium. We show that prey populations from vertical regimen were less resistant to predation than the ones from horizontal regimen. This was because prey from the horizontal regimen were under directional selection resulting in lesser within-population divergence, and an increasing resistance to predation over the evolutionary timescale. In the vertical regime, prey isolates with higher and lower degrees of resistance relative to ancestors evolved in all replicate populations, suggestive of fluctuating selection dynamics. Further, contrary to our expectations, predatory efficiency of evolvedM. xanthusisolates was either the same or lesser than the ancestor. This is likely because of social evolution of scavenging phenotypes that rely on exploiting the social mechanisms of predation such as the secretion of diffusible substances (for example antibiotics, toxins, and digestive enzymes) for extracellular digestion of prey2–4. Together, we demonstrate that community mixing affects the evolution of prey bacteria but has little effect on the hunting ability of the social predatorM. xanthus.