Range expansion can promote the evolution of plastic generalism in coarse-grained landscapes

Phenotypic plasticity is one way for organisms to deal with variable
environments through generalism. However, plasticity is not found
universally and its evolution may be constrained by costs and other
limitations such as complexity: the need for multiple mutational steps
before the adaptation is realized. Theory predicts that greater
experienced heterogeneity, such as organisms may encounter when spatial
heterogeneity is fine-grained relative to dispersal, should favor the
evolution of a broader niche. Here we tested this prediction via
simulation. We found that, contrary to classical predictions,
coarse-grained landscapes can be the most favorable for the evolution of
plasticity, but only when populations encountered those landscapes through
range expansion. During these range expansions, coarse-grained landscapes
select for each step in the complex mutational pathway to plastic
generalism by blocking the dispersal of specialists. These circumstances
provide ecological opportunities for innovative mutations that change the
niche. Our results indicate a new mechanism by which range expansion and
spatially structured landscapes interact to shape evolution, and reveal
that the environments in which a complex adaptation has the highest
fitness may not be the most favorable for its evolution.