The effects of individual non-heritable variation on fitness estimation and coexistence

Demographic theory and data have emphasized that non-heritable variation in individual frailty enables selection within cohorts, affecting the dynamics of a population while being invisible to its evolution. Here we include the component of individual variation in longevity or viability which is non-heritable in simple bacterial growth models and explore its ecological and evolutionary impacts. First, we find that this variation produces consistent trends in longevity differences between bacterial genotypes when measured across stress gradients. Given that direct measurements of longevity are inevitably biased due to the presence of this variation and ongoing selection, we propose the use of the trend itself for obtaining more exact inferences of genotypic fitness. Second, we show how species or strain coexistence can be enabled by non36 heritable variation in longevity or viability. These general conclusions are likely to extend beyond bacterial systems.