Synthetic eco-evolutionary dynamics in simple molecular environment

The understanding of eco-evolutionary dynamics, and in particular the mechanism of emergence of species, is still fragmentary and in need of test bench model systems. To this aim, we developed a variant of SELEX in-vitro selection to study the evolution of a population of ∼ 10^15 single-strand DNA oligonucleotide ‘individuals’. We begin with a seed of random sequences which we select via affinity capture from ∼ 10^12 DNA oligomers of fixed sequence (‘resources’) over which they compete. At each cycle (‘generation’), the ecosystem is replenished via PCR amplification of survivors. Massive parallel sequencing indicates that across generations the variety of sequences (‘species’) drastically decreases, while some of them become populous and dominate the ecosystem. The simplicity of our approach, in which survival is granted by hybridization, enables a quantitative investigation of fitness through a statistical analysis of binding energies. We find that the strength of individual-resource binding dominates the selection in the first generations, while inter and intra-individual interactions becomes important in later stages, in parallel with the emergence of prototypical forms of mutualism and parasitism.

Methods
Please see the paper. All the methods are clearly explained there. Our experimental design takes advantage of a selective capture mechanism where magnetic beads carrying single-stranded DNA filaments of fixed length and sequence target DNA individuals present in a DNA library based on their level of complementarity. Sequences are selected, amplified via PCR, sequenced, and analysed with the home-made codes present also in this repository.