MOORE, M.; MANAHAN, D.T.: Genotype dependant utilization of lipid and protein reserves in oyster larvae

Hybrid vigor (heterosis) is an important phenomenon in animals and plants that results in increased growth of offspring obtained from crossing inbred parents. The physiological bases for heterosis are not fully understood. Larvae of the Pacific Oyster Crassostrea gigas show strong heterosis, with higher growth rates being evident early in development (2- to 6-d-old). Changes in total protein content and major lipid classes (phospholipids, triglycerides, and long-chain hydrocarbons) were measured in oyster larvae obtained from different genetic crosses. Through early development to the feeding larval stage at 2 d, triglycerides and long-chain hydrocarbons fueled development (decreases of 50 and 33 percent, respectively). Protein content did not decrease. There was no relationship between genotype and amounts of total protein and specific lipid classes in same-sized larvae, nor was there preferential use of lipid or protein reserves during development. Larvae of C. gigas are protein-rich, with approx. four times more protein (18 ng) than lipid (5 ng) in early stages. Differential protein expression was examined using two-dimensional gel electrophoresis of proteins labeled with 35S-methionine. Faster-growing larvae showed differential expression of 10 proteins that were marginally expressed or not expressed at all in slower-growing larvae. The observed differences in protein expression could be attributed to egg effects from comparisons of different crosses (i.e., same male crossed with different females of different ‘egg quality’). We conclude that growth heterosis in larvae cannot be explained by simple differences in gross biochemical composition. Further studies of specific proteins are more likely to yield answers to the mechanisms that produce heterosis.