Effects of maternal and larval nutrition on growth and form of planktotrophic larvae

Maternal nutritional stress lowers the organic content of egg and slows the initial growth of larvae of sea urchins and bivalves. Also, larval nutritional stress changes the form and developmental sequence of larvae as an adjustment to scarce food. If effects of nutrient supplies in eggs were like those of nutrient supplies in planktonic food, then maternal nutrition would affect larval form and developmental plasticity in the same way as larval nutrition. We used natural variation in maternal habitat to test this hypothesis, using laboratory growth experiments. In the sea urchin Strongylocentrotus droebachiensis, mothers from greater depth (100 m) had smaller ovaries and smaller eggs than mothers from shallower depth (<6 m), which indicated poorer maternal nutrition at depth. Effects of maternal habitat, gonad size, and egg size on larval growth rate were significant but small compared to the effect of abundance of larval food. The growth of larvae was little affected by differences in maternal habitat that had a large effect on fecundity and some effect on egg size. There were no effects on larval body or juvenile rudiment that resembled the developmental plasticity in response to larval food. Food-limited mothers did not produce larvae with larger larval feeding apparatus or retarded development of juvenile rudiments. Uncoupled morphogenetic effects of endogenous and exogenous nutrients should be advantageous where benthic and planktonic food supplies vary independently. Finely tuned responses to stimuli may restrict the evolutionary consequences of developmental plasticity. Because maternal nutrition did not affect form of the larvae, larval form can be used at on index of planktonic conditions affecting feeding larvae.