Abstract
Abstract
Environmental heterogeneity can favor phenotypic plasticity, but whether evolutionary responses in one environment predict trait expression after environmental change remains unclear for threshold traits. Polyphenisms—plasticity characterized by discrete alternative morphs—rely on developmental thresholds, and as a consequence, are often expected to permit partial evolutionary decoupling among alternative phenotypes. Using replicated experimental evolution and artificial selection of a resource polyphenism in the nematode Pristionchus exspectatus, which develops either a predatory morph or a microbivorous morph, I tested whether evolutionary changes in morph frequency are coupled across environments. Across independent lineages, I asked whether evolutionary increase in predatory morph frequency under selection predicted phenotypic change when populations were reared back in the ancestral environment. I found a strong positive cross-environment coupling: for both sexes, lineages showing larger evolutionary responses during the first 25 generations, and across the full 50-generation experiment, also showed larger increases in predatory morph expression after environmental reversal. Artificial selection on mouth-form produced the same pattern. These results show that even a discrete threshold trait can retain strong and repeatable correlated responses across environments, consistent with morph-frequency evolution being channeled by developmental architecture shared across environments.