EFFECTS OF EGG SIZE ON POSTLARVAL PERFORMANCE - EXPERIMENTAL-EVIDENCEFROM A SEA-URCHIN

Many life-history and developmental studies of marine invertebrates as sume that eggs of species with nonfeeding larvae are large because the y provide materials for rapid development. Using the sea urchin Helioc idaris erythrogramma which has 400 mu m eggs and nonfeeding larvae, we removed an acellular, lipid-rich component from the blastula equivale nt to ca. 40% of the egg volume and ca. 50% of the organic mass. Exper imentally manipulated, reduced-lipid larvae survived well, developed i n the usual time (3.5 d), and high percentages of the original numbers metamorphosed into anatomically normal juveniles. Control juveniles w ere larger at metamorphosis, grew more, and survived longer than sibli ngs that lacked this lipid-rich material. Moderate increases in egg si ze in species with nonfeeding larvae may enhance postlarval performanc e significantly and therefore may reflect selection on early juvenile traits. The contrasts of our results and comparable experiments with f eeding larvae suggests that egg size may play fundamentally different roles in species with feeding and nonfeeding larvae. The accommodation of materials reserved for the juvenile stage should be considered amo ng hypotheses on evolutionary modification of developmental patterns.