Table 2. The effects of mutations under heat-shock and low-pH conditions.

Mutation	Assay
ID8	HS	13.64	1	116.54	0.083	3.93
T1	HS	16.37*	1	112.90NS	0.083	6.96*
T2	HS	14.73*	1	75.71*	0.083	8.42*
T3	HS	16.69*	1	78.95*	0.083	10.11*
T4	HS	15.21*	1	65.36*	0.083	9.76*
P1	HS	16.48*	1	159.55*	0.083	3.18ns
P2	HS	17.69*	1	133.99+	0.083	6.52*
P3	HS	14.65+	1	124.32ns	0.083	4.29+
ID8	pH	14.16	1	117.52	0.05	8.28
P1	pH	17.64*	1	104.24ns	0.05	10.36*
P2	pH	16.68*	1	98.83+	0.05	9.70*
P3	pH	15.44*	1	76.14*	0.05	7.75*
T1	pH	15.87*	1	145.17*	0.05	12.43ns
T2	pH	15.64*	1	105.55ns	0.05	11.73*
T3	pH	16.30*	1	132.04ns	0.05	11.63+
T4	pH	14.17ns	1	128.49ns	0.05	8.61ns

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 ; + ; * ).