Long-term evolutionary adaptation to temperature will be measured experimentally in the bacterium Escherichia coli. Originally the founding experimental line (the ancestor) was maintained at 37 C. Subsequently, groups of replicated lines were obtained after 2000 generations of exposure to 32 C, 42 C, and a daily alternation between them, as well as control lines which were maintained at 37 C. These experiments will determine the mechanisms by which each of these groups adapted to their respective temperatures. Measured variables will include changes in synthetic and transport capacities, stress resistance, and population growth performance. Lines will also be selected at higher (>42 C) temperatures to determine whether the upper thermal limit can be extended and the correlated changes responsible for increased temperature tolerance. The research proposes to address the following questions: --How rapidly can biological systems respond evolutionarily to environmental change? --Does prior evolutionary history in one environment condition or predispose ability to adapt to novel environments? --Does adaptation to a particular environment proceed by similar mechanisms or are there as many solutions as adaptive events? Specific issues addressed by this research include the rate and limits of adaptation in diverse thermal environments, the extent of trade-offs during adaptive evolution, the effect of historical environment on further adaptation, the concordance of mechanistic adaptations during evolution in similar environments, and environmental effects on mutational processes.
