Dataset for the submitted manuscript "Fitness-driven virulence evolution in Bacillus via group selection bypasses classic trade-off"

Social evolution theories of virulence posit a trade-off between pathogen replication and the cost of producing public goods, which are susceptible to exploitation by cheating mutants. This conflict constrains stable investment in shared virulence factor. Here, we demonstrate that group selection can circumvent this evolutionary constraint. Using the entomopathogenic Bacillus thuringiensis, which is safe for humans, as a model, we conducted ~200 generations of alternating serial passage in vivo (within insect host) and in vitro. This group selection yielded a stably inherited lineage with a virulence increase of over 20%, while other lineages showed fluctuating but non-significant changes in virulence. The virulent enhancement was uncoupled from changes in public goods (toxin) production and did not trade-off against replication or sporulation. Instead, higher virulence was attributable to increase within-host fitness: increased survival in the host midgut and more efficient translocation into the hemocoel. Furthermore, the competitive fitness of virulence-increased lineage was also stronger in their population. Pool-Sequencing Time Series analysis revealed that the higher virulence lineage showed the frequencies of certain genes remained at a low level, while other lineages showed more similar polymorphism with in vitro passaged control. This divergence in evolutionary trajectory underscores that the adaptation to the host was the primary driver of increased virulence. Our findings reveal a non-canonical evolutionary trajectory to virulence that operates through group-selected fitness benefits without public goods trade-offs.