Parallel Evolution of Whole Viral Genomes Seen in Long-Term Phage Experiment

Bacteriophage φX174 populations evolved largely in parallel at the level of their entire genomes, not just at individual mutation sites, according to a long-term evolution experiment reported in PLOS Biology. Researchers led by Roland R. Regoes and colleagues followed four independent viral populations for 412 generations, sequencing more than 80,000 phage genomes that represented 884 distinct genotypes.

The experiment combined high-throughput sequencing with rapid experimental evolution, an approach designed to track the genetic diversification of populations with high mutation rates in unusual detail. The team deliberately avoided imposing any selection pressures beyond those inherent in the bacterial host cell environment, because one goal was to evaluate phylodynamic methods, which infer key parameters of population history from genetic data and assume neutral evolution.

Despite the absence of imposed selection, the four lines did not evolve independently at random. The patterns of viral diversification produced largely non-congruent genotype distributions across the replicate populations, yet the researchers documented multiple instances of parallel evolution. Unlike previous observations of parallelism in viral evolution, which typically involve the same mutations arising at single genetic sites, the parallelism here extended to full-length genomes.

Computer simulations that recapitulated the experiments in great detail showed that this degree of parallelism is inconsistent with neutral evolution. In other words, the repeated genomic trajectories cannot be explained by chance alone under the neutral assumptions that underpin many phylodynamic analyses.

The findings carry a practical warning for evolutionary biology. When the researchers applied phylodynamic analysis to their data, the observed extent of parallel evolution biased estimates of migration rates, causing the method to wrongly infer significant migration between the independent evolution lines. Because the four populations were physically separate, any inferred migration was an artifact of their shared evolutionary tendencies rather than actual movement of viruses between lines.

The authors note that their approach is applicable to many other viruses and could enable advanced population genetic investigations into phenomena related to genetic linkage across the genome. For studies that use genomic data to reconstruct viral population histories, the results suggest caution: parallel evolution within lineages can mimic signals, such as migration, that phylodynamic methods are designed to detect.

Subject of Research: Parallel evolution of full-length viral genomes in a long-term bacteriophage φX174 evolution experiment

Article Title: Full-length genomes evolve in parallel in a long-term evolution experiment with phage φX174

Article References: Bons, E., Chabas, H., MacDonald, H., Escalera Ledermann, A., Ösze, S., Dunstan, J., Ochsner, N., Angst, D. C., Bonhoeffer, S., & Regoes, R. R. (2026). Full-length genomes evolve in parallel in a long-term evolution experiment with phage φX174. PLOS Biology, 24(10), e3004064. https://doi.org/10.1371/journal.pbio.3004064

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3004064

Keywords: phage φX174, parallel evolution, experimental evolution, phylodynamics, high-throughput sequencing, bacteriophage, neutral evolution, genetic diversification, migration rate estimation, viral genomics, Full-length, genomes