Prebiotically Plausible Vesicle Populations Can Respond to Selection for Greater Turbidity via Emergent Cooperative...

Adaptive evolution has long been hypothesized to be possible in the absence of genetic molecules, but experimental evidence remains lacking. Fatty acid vesicles can spontaneously grow and divide and might therefore be capable of nongenetic inheritance, making them ideal for exploring the emergence of prebiotic evolution. In this study, we tested whether vesicle populations can respond to artificial selection for greater turbidity and, if so, whether that response can be tied to an inheritance-like mechanism. We prepared 192 independent vesicle populations, incubated them for 24 h, and then selected half of the populations to propagate into the next generation. The populations to propagate were picked either randomly, representing drift controls, or were those with the greatest turbidity, representing selection. Population propagation involved resuspension, transfer into fresh buffer, feeding with an amphiphile stock, and then incubating for the next 24 h. In three replicate experiments run for at least 10 generations, we observed consistently greater turbidity in selection compared with drift lineages. This was accompanied by a reduction in the heritability (the regression slope between parent and offspring turbidities) of the selected lineages. We conducted additional experiments to evaluate whether this response to selection is caused by a simple carryover effect or reflects cooperative dynamics where vesicles from a parental population affect newly formed vesicles in the next generation. The response to selection is much lower when the resuspension step was omitted and/or if new amphiphiles were provided as preformed vesicles. Combined with fluorescence analyses of the resuspension and feeding processes, these results suggest that cooperative vesicle dynamics occur in cases where a small number of intact vesicles from a parental generation interact with an excess of incorporated amphiphiles. Overall, this study represents the first experimental finding of a response to artificial selection in prebiotic chemistry.