experimental test of evolutionary trade-offs during temperature adaptation

• Published in: Proceedings of the National Academy of Sciences - PNAS 2007-05, Vol.104 (Suppl 1), p.8649-8654
• Main Authors: Bennett, Albert F, Lenski, Richard E
• Format: Article
• Language: English
• Subjects: Adaptation, Biological; Biological adaptation; Biological Evolution; Colloquium Papers; Confidence limits; Correlated responses; E coli; Ecological competition; Environment; Escherichia coli; Escherichia coli - physiology; Evolution; Evolutionary biology; Evolutionary genetics; Genetic linkage; High temperature; Low temperature; Phenotypic traits; Phylogeny; Selection, Genetic; Temperature
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0702117104

We used experimental evolution to test directly the important and commonplace evolutionary hypothesis that adaptation, increased fitness within the selective environment, is accompanied by trade-off, a loss of fitness in other nonselective environments. Specifically, we determined whether trade-offs at high temperature generally and necessarily accompany genetic adaptation to low temperature. We measured the relative fitness increment of 24 lineages of the bacterium Escherichia coli evolved for 2,000 generations at 20°C and the relative fitness decrement of these lines at 40°C. Trade-offs at the higher temperature were examined for their generality, universality, quantitative relationship, and historical contingency. Considering all 24 lines as a group, a significant decline in fitness was found at 40°C (mean decline = 9.4%), indicating the generality of the trade-off effect. However, in a lineage-by-lineage analysis, only 15 of 24 showed a significant trade-off, and one lineage increased fitness at high temperature. Thus, although general, trade-offs were not universal. Furthermore, there was no quantitative association between the magnitude of adaptive fitness increment at 20°C and fitness decline at 40°C, and no effect of lineages' historical thermal environment on either their improvement at 20°C or the extent of their trade-off at high temperature. We do not yet know the underlying mechanisms responsible for the trade-off, but they are sufficiently prevalent to drive a general effect. However, approximately one-third of the experimental lineages achieved low-temperature adaptation without detectable high-temperature trade-offs; therefore, it cannot be necessary that every change conferring benefit in cold environments has a negative effect on function in warmer environments.