MEYER, E.*; HAAG, A.L.; VON DIPPE, P.; HEDGECOCK, D.E.; MANAHAN, D.T.; University of Southern California, Los Angeles: Physiological Genomics and the Identification of Genes Involved in Differential Growth Rates of Bivalve Larvae

Hybrid vigor is a very important process in evolutionary biology. Using genetically controlled crosses of animals and plants, the phenomenon of enhanced growth rates for hybrids has been repeatedly observed for many decades. Very little is known, however, of the physiological and biochemical mechanisms responsible for hybrid vigor in any organism. We addressed this issue from the standpoint of global, differential gene expression by quantifying the differences in gene expression levels between fast-growing �hybrid� larvae and slow-growing �inbred� larvae of the Pacific oyster Crassostrea gigas. Using high-throughput DNA sequencing (�MPSS�, Lynx Therapeutics), a total of 3.2 million transcripts were analyzed. Of these, 220 genes were identified by computational analysis as being differentially expressed in hybrid larvae. To date, we have cloned and partially sequenced 109 of these �hybrid vigor� genes. Tentative identification of some of these genes include ubiquitin transcripts, mitochondrial rRNA�s, and mitochondrial NADH dehydrogenase subunits. These results suggest that macromolecular synthesis and turnover, and metabolic efficiency are likely to be key components of enhanced growth rates observed in hybrid larvae. The combination of experimental crosses, quantitative genetics, and physiological genomics can provide new insights into the mechanisms of differential growth rates and other complex physiological traits.