Plant & Animal Genome IX Conference

Workshop: Aquaculture
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GENOMIC APPROACHES TO UNDERSTANDING HETEROSIS AND IMPROVING YIELD OF FARMED PACIFIC OYSTERS

¹ University of California, Davis, Bodega Marine Laboratory, Bodega Bay, CA, 94923-0247, USA

² Department of Biological Sciences, University of Southern California, Los Angeles, CA, 90089-0371, USA

³ Lynx Therapeutics, Inc., 25861 Industrial Blvd. Hayward, CA, 94545, USA

According to FAO statistics, the Pacific oyster is the most farmed aquatic organism in the world. Large selection and crossbreeding efforts are underway to improve yield. Previously, we demonstrated classical heterosis (superior yield of F₁ hybrids compared to inbred parents) but were unable to map its genetic basis, owing to distortions of Mendelian segregation ratios, which had been reported for bivalves as early as 1975. We subsequently showed that oysters carry a large load of highly deleterious recessive mutations, which provides a coherent explanation for both segregation distortion and heterosis (Launey & Hedgecock, PAG VII). Now, we are constructing a moderately dense linkage map to facilitate QTL mapping of heterosis genes, using microsatellite analyses of early larvae. We are simultaneously pursuing the physiological and functional genomic basis of heterosis in order to identify early indicators of growth potential. The physiological causes of growth heterosis appear to be greater metabolic efficiency, lower protein turnover, and higher feeding rates and efficiencies in hybrids. Differences in oxygen consumption have been detected as early as 15 h post-fertilization. In collaboration with Lynx Therapeutics, Inc., we are cloning cDNA libraries obtained from 6-day old inbred and hybrid larval oysters on plastic micro-beads (Brenner et al. 2000 PNAS USA 97:1665). Sequence information derived from a second Lynx technology, Massively Parallel Signature Sequencing (MPSS«), will allow characterization of the gene expression profiles underlying heterosis. Micro-array technology can then be used to quantify the expression of critical heterosis genes at early larval stages.