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TABLE 12.3 Fitness at 40°C of 20°C-Selected Lineages and Their Historical Progenitors, Each Measured Relative to the Common Ancestor

 

−1

−2

−3

32

0.963 ± 0.021

1.028 ± 0.064

0.980 ± 0.029

32/20

0.849 ± 0.063

0.549 ± 0.178

0.900 ± 0.047

37

1.102 ± 0.029

0.616 ± 0.071

0.993 ± 0.031

37/20

0.881 ± 0.067

0.608 ± 0.145

0.889 ± 0.021

42

1.153 ± 0.050

1.089 ± 0.059

1.117 ± 0.041

42/20

0.984 ± 0.054

0.934 ± 0.061

0.974 ± 0.033

32–42

1.056 ± 0.040

1.079 ± 0.058

1.064 ± 0.067

32–42/20

0.916 ± 0.100

0.963 ± 0.044

1.010 ± 0.057

Contents and notations are as in Table 12.1.

TABLE 12.4 Change in Fitness (ΔW) at 40°C of 20°C-Selected Lines Compared with Their Historical Progenitors

 

−1

−2

−3

32/20 vs. 32

−0.114

−0.478

−0.080

 

P < 0.001

P < 0.001

P = 0.003

37/20 vs. 37

−0.220

−0.007

−0.104

 

P < 0.001

P = 0.454

P < 0.001

42/20 vs. 42

−0.169

−0.156

−0.144

 

P < 0.001

P < 0.001

P < 0.001

32-42/20 vs. 32-42

−0.140

−0.116

−0.053

 

P = 0.004

P = 0.001

P = 0.088

Contents and designations are as in Table 12.2.

one might be tempted to “explain away” these nonsignificant results as false negatives that reflect limited statistical power, that explanation was rejected, as follows. For 3 of the 24 lines, their correlated fitness changes at 40°C were positive rather than negative and, in one case, the correlated improvement was significant. To avoid the possibility of a false positive in the unexpected direction, additional fitness assays were performed (with twice the original level of replication) for that exceptional line, as well as for two others that showed significant and nonsignificant trade-offs. The very same patterns emerged in these new and independent assays for all three strains, including confirmation of the unexpected gain in fitness at 40°C in the line of interest. Hence, contrary to the general pattern and prediction, one line significantly increased in fitness at high temperature while adapting to low temperature.



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