MINER, BG; VONESH, JR: Implications of Environmental Variability for Phenotypic Plasticity

Many organisms have evolved the ability to change their morphology in response to changes in the environment (phenotypic plasticity). To date, experimental studies of phenotypic plasticity have focused exclusively on phenotypic changes in different but constant treatments. Yet, we know that natural environments are variable. Despite this, no study has investigated how variance may affect inducible morphologies. Our study addresses this question with sea urchin larvae (plutei). Plutei have inducible feeding structures that increase in length when food is scarce and decrease when food is abundant. We reared plutei of Lytechinus variegatus under three different treatments in which the mean food concentration was the same (4 phytoplankton cells/microliter) but the variance differed (standard deviation (SD) = 0, 2, and 4). The constant food treatment (SD = 0) was fed 4 cells/microliter every two days, and the variable treatments (SD = 2 and 4) were fed alternating concentrations of 6 and 2 cells/microliter, and 8 and 0 cells/microliter respectively every two days. We found that plutei in the constant food treatment (0 SD) produced significantly longer feeding structures, had more energy, and developed faster, than larvae in the variable food treatments. These results are the first to show that inducible morphologies can respond to differences in variance, and emphasize the need to consider and quantify variance when studying phenotypic plasticity.