Experimental evolution toward extinction in a molecular host-parasite system

Theoretically, coevolution with parasitic replicators is critical for the evolution of primitive life, but experimental verification is limited. We previously conducted co-evolutionary experiments using an RNA-protein replication system over 500 generations, achieving spontaneous diversification of host and parasitic RNAs into five distinct lineages with robust co-replication. Here, we present contrasting results from a much longer-term coevolution experiment over 1,600 generations using a flow reactor with increased dilution frequency, in which we observed reduced diversity and frequent extinctions in later stages. Co-replication assays revealed that the loss of diversity primarily resulted from shortened reaction time due to frequent dilution. Analysis of evolved RNA clones suggested that frequent extinctions resulted from the dominance of host species that either lost parasite resistance or exhibited reduced replication ability. These findings demonstrate the critical importance of environmental parameters, such as dilution frequency, in enabling the sustainable evolution of primitive replicators toward the emergence of life.