An investigation into the phenotypic consequences of triploidy and aneuploidy in two cupped oyster species, Crassostrea virginica and Crassostrea gigas

Two cupped-oyster species, Crassostrea virginica and Crassostrea gigas are economically and ecologically important species along the East and West coasts of the US, respectively. Unlike other animals, they have the ability to tolerate different chromosomal conditions and that increases their genetic value. Both aneuploid and triploid conditions are tolerated and represent an unique opportunity to study chromosomal variation and its effects on phenotype in animals.; Somatic aneuploidy in the gill tissue of C. virginica to see if the negative correlation between size and aneuploidy observed in C. gigas was a more general phenomenon. One hypothesis proposed to explain poorer growth in aneuploid oysters is that the progressive haploidization of the aneuploid process unmasks alleles deleterious to growth. While aneuploidy was present in the gill tissue from C. virginica, it was not always correlated with smaller size. In 2 out of 3 progenies studied, size was not correlated to the level of aneuploidy; therefore, somatic aneuploidy in gill tissue is not always the major determinant of growth.; The suppression subtractive hybridization (SSH) technique was used to construct complementary libraries of partial transcripts that were cloned and sequenced to identify transcriptional differences between diploids (2n=20) and triploids (3n) and between diploids and trisomics (2n+1) by season, by functional category, and in individual genes. Evaluation of this method suggests that it was more powerful when the actual differences between the oysters were small, either small differences in the chromosome condition, or in the level of activity of the oysters. Almost 100 different clones with high homology to known genes are discussed in the context of the observed phenotypic differences between ploidy variants. Gene expression differences were quantitatively compared using real-time RT-PCR. Many genes that were up regulated in the diploids in the spring and summer switched to being up-regulated in the triploids in the fall, the winter, or both. Several of the genes up regulated in triploids during those seasons were involved in lipid metabolism. In general, expression in triploids and trisomics compared to diploids showed neither a gene dosage effect nor dosage compensation, suggesting gene copy number does not determine transcription levels.