When Does the Probability of Evolutionary Rescue Increase with the Strength of Selection despite a Potential...

AbstractPopulations may be rescued from extinction via sufficiently rapid adaptive evolution. Evolution is faster with stronger selection, but this may come with a demographic cost, creating opposing effects on evolutionary rescue. The outcome of this trade-off influences the optimal strategy for avoiding herbicide/drug resistance evolution. Here we examine the effect of stronger selection on rescue when demography and selection covary, across four models of evolutionary rescue. We find that stronger selection cannot facilitate rescue in two quite different population genetic models unless selection is associated with higher absolute fitness of rescue homozygotes. Similarly, in a quantitative genetic model of rescue under an abrupt environmental shift, stronger selection accelerates evolution but leaves maximum fitness unchanged and cannot facilitate rescue. We also explore a quantitative genetic model of rescue in a gradually changing environment, generalizing the finding that an intermediate selection strength maximizes survival at steady state to a wider class of fitness functions.