The red queen beats the jack-of-all-trades: The limitations on the evolution of phenotypic plasticity and niche breadth

The evolution of niche breadth or phenotypic plasticity is often assumed to be limited by negative genetic correlations among fitness in different environments, but these trade-offs are rarely observed. Many other constraints can reduce the mean niche breadth of species. This article discusses one of these limitations-that species with broader niche breadths can have a slower rate of evolutionary response. Species with narrower niche breadths have higher probabilities of fixing beneficial alleles, taking less time to do so; they have fewer deleterious alleles drifting to fixation (a lighter drift load) and a lower frequency of deleterious alleles at mutation-selection equilibrium (a lighter mutation load). These patterns are true even with no correlation at all between fitness in different environments; no trade-offs are assumed. Furthermore, niche breadth is likely to evolve to be more narrow, because of the association between location and alleles favored in local habitats for individuals with reduced migration, assortative mating, or habitat selection. The evolution of niche breadth and plasticity is not a simple function of the fitness in different environments; understanding niche breadth evolution requires consideration of the limitations of the evolutionary process per se.