Substrate level variation in the eggs and embryos of the American oyster Crassostrea virginica (gmelin)

Abstract

Parentally derived resources vary in the eggs of marine invertebrates, affecting the pattern of resource allocation, utilization and subsequent larval viability. The eggs from twelve oysters, Crassostrea virginica, were collected and measured for levels of soluble protein, total lipid and glycogen before and after fertilization. The twelve females were spawned in 3 groups of 4 at different times during the spawning season. Half-sib families were created by fertilizing the eggs of all 4 females within a spawn with the sperm from the same male. Initial levels of all 3 substrates differed significantly between spawns (p< 0.0167) and between females within spawns (p< 0.0001). The eggs collected in May (spawn Al had the highest mean initial lipid level (3.0 ng/egg). These same embryos utilized lipid and synthesized protein. Initial lipid levels declined over the spawning season to a low of 1.3 ng/egg in early September (spawn C). Further experiments with 14C-glucose revealed no differences between females in uptake, accumulation or deputation rates of 14C from either 14C-U-glucose or 14C-6-glucose. The C-6 carbon of glucose was observed to be preferentially retained during embryogenesis. Corresponding numbers of larvae surviving to each time point were also determined for the substrate level experiments. Final survival was highly variable (1 3% to 99%) and was correlated with initial lipid levels, lipid utilization and protein synthesis. Glycogen levels and utilization were not correlated to survival but glycogen utilization was included as the least significant factor in a regression equation for survival that also included initial lipid level, lipid metabolism and protein metabolism (r= .96). These results support earlier findings on the utilization of lipids during embryogenesis and suggest a seasonal variation in this parameter. Significant roles for glycogen utilization and protein synthesis in embryonic survival are also revealed.