Experimental and theoretical support for costs of plasticity and phenotype in a nematode cannibalistic trait

Abstract

Developmental plasticity is the ability of a genotype to express multiple phenotypes under different environmental conditions and has been shown to facilitate the evolution of novel traits. However, while associated costs of both plasticity and phenotype have been theoretically predicted, empirically such costs remain poorly documented and little understood. Here, we use a plasticity model system, hermaphroditic nematode Pristionchus pacificus, to experimentally measure these costs in wild isolates under controlled laboratory conditions.P. pacificus can develop either a bacterial feeding or predatory mouth morph in response to different external stimuli, with natural variation of mouth-morph ratios between strains. We first demonstrated the cost of phenotype by analyzing fecundity and developmental speed in relation to mouth morphs across the P. pacificus phylogenetic tree. Then, we exposed three P. pacificus strains to two distinct microbial diets that induce strain-specific mouth-form ratios. Our results indicate that a highly-plastic strain does shoulder a cost of plasticity, i.e., the diet-induced predatory mouth morph is associated with reduced fecundity and slower developmental speed. In contrast, a non-plastic strain suffers from the cost of phenotype in unfavorable conditions, but shows increased fitness and higher developmental speed under favorable conditions. Furthermore, we computationally illustrate the consequences of the costs of plasticity and phenotype on the population dynamics in spatially-homogeneous and spatially-structured populations using empirically-derived life history parameters for modeling. This study provides comprehensive support for the costs of plasticity and phenotype based on empirical and modeling approaches.