Experimental Evolution and Its Role in Evolutionary Physiology

Four general approaches to the study of evolutionary physiology—phylogenetically-based comparisons, genetic analyses and manipulations, phenotypic plasticity and manipulation, and selection studies—are outlined and discussed. We provide an example of the latter, the application of laboratory selection experiments to the study of a general issue in environmental adaptation, differences in adaptive patterns of generalists and specialists. A clone of the bacterium Escherichia coli that had evolved in a constant environment of 37°C was replicated into 6 populations and allowed to reproduce for 2,000 generations in a variable thermal environment alternating between 32 and 42°C. As predicted by theory, fitness and efficiency of resource use increased in this new environment, as did stress resistance. Contrary to predictions, however, fitness and efficiency in the constant ancestral environment of 37°C did not decrease, nor did thermal niche breadth or phenotypic plasticity increase. Selection experiments can thus provide a valuable approach to testing hypotheses and assumptions about the evolution of functional characters.