Simple case of prebiotic evolution: vesicle populations can respond to selection for greater turbidity via emergent cooperative dynamics

Adaptive evolution has long been hypothesized to be possible in the
absence of genetic molecules, but experimental evidence remains lacking.
Fatty acid vesicles represent an intriguing model to study the emergence
of prebiotic evolution, since they can spontaneously grow and divide and
have been hypothesized to be capable of non-genetic inheritance. In this
study we conducted multiple experiments to test 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 96 independent vesicle populations, incubated them for 24
hours and then selected half the populations to propagate into the next
generation. The populations to propagate were picked either randomly,
representing drift controls, or were the populations 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 hours. In three replicate
experiments run for at least 10 generations, we observed consistently
greater turbidity in selection lineages compared to drift, as well as a
reduction in the heritability (i.e., the correlation between parent and
offspring turbidities). 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 the parental
generation affect newly formed vesicles in the offspring generation. The
response to selection is much lower if we omitted the resuspension step
and/or if we did not feed transfers with amphiphiles but instead mixed
them we pre-formed vesicles. Combined with imaging and other analyses of
the resuspension and feeding process, these results suggest that
cooperative vesicle dynamics occur, where a small number of intact
vesicles from a parental generation alters the dynamics of new vesicle
formation following food addition. Overall, this study represents the
first experimental finding of a response to artificial selection in
prebiotic chemistry.