Long-Term Evolution Experiments

Long-term evolution experiments are a staple of experimental evolution because they are easy to implement, offer opportunities for discovery, are open ended, and allow the dynamics, repeatability and diversity of adaptive responses to be explored on a human time scale. Early studies reached a consensus that adaptive evolution was surprisingly repeatable, that selection favors rapid uptake and metabolism of the limiting nutrient, disfavors unnecessary gene expression, is initially rapid and then slows. Later studies and technical advances revealed that selective sweeps are characterized by clonal interference among numerous lineages carrying similar mutations that confer similar selective benefits. Trade-offs and the evolution of specialists and generalists and difficulties in distinguishing mechanisms of specialization are reviewed. Experimental examples of character displacement, adaptation with diauxie generating an endogenously fluctuating environment, the evolution of a competition-colonization trade-off and an adaptive radiation are discussed.