The effects of mutations under heat-shock and low-pH conditions.

Selection for increased growth rate, , occurs during the growth phase of each transfer which lasts for time, represented as fraction of an hour, . In the absence of host organisms, viral particles decay at rate for a time, . During this second stage of the regime, we subjected virus populations to either extreme heat (80°C) or low pH (1.5). Fitness, , is measured as a combination of the growth and decay rates and the time spent under each condition, . HS, heat-shock; pH, pH-shock. P values result from pairwise comparisons with sequential Bonferroni corrections for multiple comparisons to determine differences from the ancestor, ID8 (NS ; + ; * ).The effects of mutations under heat-shock and low-pH conditions.