Abstract
BACKGROUND: Echinoid larvae are known to display food-induced phenotypic plasticity, where larvae alter their morphology and physiology to reflect available food levels. The aim of this study was to describe the induction and reversal of morphological and physiological plasticity through the entirety of larval development of the sand dollar Dendraster excentricus. RESULTS: When larvae fed a low algal ration were switched to high food conditions at 10-, 20-, and 30-day post-fertilization, we observed rapid induction of the high-fed phenotype as indicated by decreases in postoral arm length (POAL) as well as changes in assimilation and growth efficiencies. Switched larvae required more time to develop, but due to physiological changes in assimilation efficiency, they expended the same total amount of energy to achieve metamorphic competence as constantly high-fed larvae. These morphological results were also confirmed by tracking individual larvae in separate experiments. When larvae were switched from high to low food conditions, short-armed larvae rapidly experienced significant increases in POAL. CONCLUSIONS: These results establish that plasticity responses in echinoid larvae are both reversible and inducible throughout larval development and result in significant adaptive benefits in terms of energy use. Our single larval experiments facilitate future analyses that can explore the genetic and molecular underpinnings of phenotypic plasticity.