MCALISTER, J.S.; PODOLSKY, R.D.; UNC-Chapel Hill; UNC-Chapel Hill: Costs and limits of phenotypic plasticity during development of Lytechinus variegatus
Theoretical models predict that the evolution of phenotypic plasticity, differential phenotypic expression in heterogeneous environments, may be constrained by costs and limits. Despite careful empirical studies in several biological systems, significant costs and/or limits of adaptive phenotypic plasticity have not been clearly demonstrated. I am investigating whether costs and limits are associated with phenotypic plasticity of feeding structures formed by echinoid larvae. In response to food limitation, larvae of several echinoid species elongate a food collecting ciliated band by lengthening larval arms. Although this response can enhance feeding under low food conditions, costs and/or limits may constrain the expression of plasticity in more-plastic genotypes. Costs in the plasticity of ciliated band length may be detected if for a given phenotype; more-plastic genotypes have lower fitness. Limits are indicated if the developmental range of more-plastic genotypes is narrower than for less-plastic genotypes. I used a quantitative genetic breeding design to test these two predictions. Gametes of the sea urchin Lytechinus variegatus were fertilized in a 6 male x 2 female full-sib, half-sib breeding design. This design was replicated in 4 temporally separate blocks to produce a total of 48 full-sib families. Components of phenotypic variance (VG, VE, VGxE) were determined for multiple morphological traits of approximately 2000 individuals reared at two different food levels. Trait-specific measures of degree-of-plasticity (reaction norm slope) were estimated for each individual and a measure of fitness (energetic content) was obtained for each genotype. I am analyzing the data to determine if costs and/or limits are correlated with phenotypic plasticity of ciliated band length. The results of this analysis may indicate the extent to which costs and limits constrain the evolution of phenotypic plasticity.
