Comparative morphometrics of echinoderm larvae. I. Some relationships between egg size and initial larval form in echinoids

Abstract

Egg protein content, and presumably total organic content (parental investment), was linearly related to egg volume among seven species of echinoids with planktotrophic larval development: Strongylocentrotus droebachiensis (O.F. Müller), S.purpuratus (Stimpson), S.franciscanus (A. Agassiz), Dendraster excentricus (Eschscholtz), Heterocentrotus mammillatus (Klein), Colobocentrotus atratus (Linnaeus), and Tripneustes gratilla (Linnaeus). Initial larval size and feeding capability, at the 2-armed and 4-armed pluteus stages, were positively correlated with egg size. The complexity of larval shape, as ciliated band length or total arm length relative to body length, was independent of egg size. Initial feeding efficiency, defined as the ratio of feeding capability to larval respiratory electron transport system (ETS) activity, was inversely related to egg size. This was the result of a strong dependence of metabolism on body size. Important differences in the egg size and larval form relationships were observed among the different echinoid families and between geographic regions. It is predicted that species with larger eggs and larger initial larvae will either remain larger at each stage of development or develop to a given stage faster than species with small eggs. These relationships between egg size and larval form may constrain selection for certain reproductive or larval traits such as egg size, fecundity, larval form, development rate, total development period, and size at metamorphosis, thereby limiting the evolutionary flexibility of reproductive pattern.