MCALISTER, J.S.*; PODOLSKY, R.D.; Univ. of North Carolina at Chapel Hill; Univ. of North Carolina at Chapel Hill: Testing for costs of phenotypic plasticity during development of Lytechinus variegatus
Phenotypic plasticity can increase organismal fitness by altering phenotypic expression in heterogeneous environments. Theory predicts however, that the evolution of optimal plastic phenotypes could be constrained by various costs. Despite careful tests, significant costs have not been clearly demonstrated in several systems where plasticity is thought to be adaptive. I am investigating whether excess production costs 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 investing in larval arm growth. Although this response can enhance feeding under low food conditions, the ability to express plasticity may entail costs in more-plastic genotypes. A hypothesis of costs in the plasticity of ciliated band length would be supported if (1) there were significant genetic variation for plasticity and (2) for a given phenotype, less-plastic genotypes had higher fitness in all environments. I used a quantitative genetic breeding design to address these two predictions. Gametes of the sea urchin Lytechinus variegatus were fertilized in an 8 male x 4 female chain block breeding design to produce 16 families. Components of phenotypic variance (VG, VE, VGxE) were determined for individuals reared in two different food level environments, and a plasticity measure (reaction norm slope) was estimated for each genotype. Plasticity varied significantly among genotypes, indicating genetic variation for plasticity of larval arm length. I am currently testing whether a fitness measure (energetic content) is lower for more-plastic genotypes and will use a regression of plasticity vs. fitness to determine if costs constrain the evolution of phenotypic plasticity.
