Effect of mutation supply on population dynamics and trait evolution in experimental microbial community

Mutation supply can influence eco-evolutionary dynamics in important ways
which have received little attention. Mutation supply determines key
features of population genetics, such as the pool of adaptive mutations,
evolutionary pathways available, and importance of processes such as
clonal interference. The resultant trait evolutionary dynamics, in turn,
can alter population size and species interactions. However, controlled
experiments testing for the importance of mutation supply on rapid
adaptation and thereby population and community dynamics are lacking. To
close this knowledge gap, we performed a serial passage experiment with
wild-type Pseudomonas fluorescens and an isogenic xerD mutant with reduced
mutation rate. Bacteria were grown at two resource levels in combination
with the presence of a ciliate predator. We found that a higher mutation
supply enabled faster adaptation to the low-resource environment and
anti-predatory defense. This was associated with higher population size at
the ecological level and better access to high-recurrence mutational
targets at the genomic level for the strain with higher mutation supply.
In contrast, mutation rate did not affect growth under high-resource
level, possibly because of more permissive conditions or high population
size saturated in mutations. Our results demonstrate that intrinsic
mutation rate influences population dynamics and trait evolution
particularly when population size is constrained by extrinsic conditions.