QUANTITATIVE GENETIC-ANALYSIS OF GROWTH IN LARVAL SCALLOPS (PLACOPECTEN-MAGELLANICUS)

We estimated the broad-sense heritability of larval size in 20 full-si b families of the giant scallop, Placopecten magellanicus (Gmelin, 179 1) grown in laboratory culture in August and September 1991. The goal was to compare scallops with other bivalves which have been shown to h ave significant heritabilities for larval growth. Secondly, we estimat ed the lipid content of oocytes from female parents, since this is hyp othesized to affect larval growth and survival. Finally, we estimated the among-family variation in mortality from 4 to 21 d as a test of po ssible genetic variation for viability among larval scallops. Signific ant genetic variation (h(2) = 1.10 to 1.24) was estimated for larval s hell length at 4, 14, and 21 d. There was a significant correlation (r = 0.66) between larval size at 4 d and lipid content of oocytes, but only when two females with high levels of lipid oocyte-l were excluded as outliers. There was no correlation between larval size at 14 and 2 1 d and lipid content of oocytes. Mortality among families from 4 to 2 1 d was high (69 to 97%), and was significantly different among famili es. These results indicate that there is significant heritability for larval growth which is largely independent of the lipid content of the oocytes. A high heritability for larval growth may indicate that this trait is only weakly correlated with fitness.