Plant & Animal Genome VI Conference

W8

SEX DISTRIBUTION IN OYSTER POPULATIONS AND DNA MARKERS

1. International Center for Oyster Genomics, Miyazu, Kyoto
2. Department of Molecular Biology, Keio University School of Medicine, Shinjuku, Tokyo

It has been known that the oysters are monoecious. Among them, the larviparous oysters (i.e. O. edulis) change sexual phase regularly in a definite rhythm, while the oviparous oysters (i.e. C. gigas and C. virginica) may change sex during the interval between two breeding seasons. As a step toward understanding the molecular mechanisms of sex differentiation and change, we have begun the oyster genome project. For this aim, we first re-examined the sex distribution of the C. gigas populations by detailed anatomical and histological observations. We found there are many hermaphrodites during early period of maturation and their number declines toward reproductive season by increasing individuals with distinct sex. The gonads of hermaphrodites were classified into three groups by their contents; complete ovary and complete spermary, spermary with ovum, ovary with sperm. We observed the contents of the monoecious gonad change before reproductive season. Furthermore, we established a simple assay by adapting the method developed for M. edulis to distinguish each of three sex types of oysters (monoecious, female and male) by measuring the certain lipid components. These observations add a new insight in the classic observation that sex change occurs in oysters before reproductive season.

We are now in the process of isolating DNA markers from a genomic BAC library of the oyster with well-defined sex.