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Abstract

Developmental plasticity has been proposed as a vehicle for phenotypic diversification in animals and plants. However, few studies test the morphological potential of plastic traits in a phylogenetic framework. Here, we test the evolutionary consequences of developmental plasticity in the nematodes of Diplogastridae, which include species with moveable teeth, a predatory lifestyle, and in many cases stomatal dimorphism. We have studied the evolution of diplogastrid feeding-structures by analyzing changes of form and complexity, particularly in the context of a robust molecular phylogeny. In our analysis, stomatal dimorphism was supported to be an ancestral feature of Diplogastridae. The origin of the plasticity coincided with the appearance of predatory teeth and immediately preceded a radiation of complex feeding-forms. Comparative morphometric analyses show that developmental plasticity is associated with a shift to increased rates of phenotypic evolution. Furthermore, the fixation of a single phenotype has coincided with a further increase in disparity of stomatal shape. Thus, a macroevolutionary “pulse” of plasticity and the subsequent fixation of forms have allowed evolutionary novelties, increased morphological complexity, and rapid morphological exploration following a release from developmental constraints.