Question 1

How many replicate lines does an evolution experiment need?

Accepted Answer

Enough that parallel outcomes can be distinguished from chance, which usually means at least six independent lines per treatment, and more when the expected effect is small. Replicates cost freezer space and sequencing capacity, so the number must be settled during design rather than expanded midway through an experiment.

Question 2

How are phage mutation rates estimated reliably?

Accepted Answer

Fluctuation tests remain standard, counting variants that escape a restrictive host across many parallel cultures and fitting the distribution to estimate rate. Mutation accumulation lines with severe bottlenecks offer a second route that minimises selection. Both require correction for the possibility that some variants carry a fitness cost during growth.

Question 3

What distinguishes genuine low frequency variants from sequencing error?

Accepted Answer

Depth of coverage, base quality distributions, strand balance, and position within reads all inform the call. Sequencing the ancestral population provides an empirical error floor, and replicate library preparation shows which rare calls reproduce. Variants below roughly one percent need particularly careful treatment and independent confirmation.

Question 4

How is recombination detected within a phage population?

Accepted Answer

Phylogenetic incongruence between genome regions, breakpoint scanning methods, and linkage disequilibrium decay all provide evidence. Each rests on assumptions about substitution rates and population structure that can fail for closely related genomes. Reporting agreement across several independent methods gives a more defensible conclusion than any single test.

Question 5

How can selection be measured rather than merely inferred?

Accepted Answer

Direct competition between an evolved variant and a marked ancestor under defined conditions yields a selection coefficient. Reconstructing candidate mutations in a clean background separates the causal change from hitchhikers. Frequency trajectories alone rarely suffice, because linkage and clonal interference produce patterns that mimic direct selection.

Question 6

How should host defence diversity shape the experimental design?

Accepted Answer

Host panels should span the defence systems relevant to the question, since restriction, abortive infection, and adaptive immunity impose different pressures and select different escape routes. Sequencing host genomes beforehand reveals which systems are present, preventing the confusion that follows when an unrecognised defence drives the observed outcome.

Microbiology

Microbiology

Research Frontiers in Bacteriophage Population Dynamics and Evolution