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Because of the loss of wild populations, most oysters consumed in restaurants today are produced in hatcheries and grown to market size by extensive aquafarming. The demand for eastern oysters has been increasing and is poised for continued growth. As the industry grows, it will become increasingly important for breeding programs to broaden goals and address more traits that may be of interest to the commercial half-shell market. The appearance of the oyster’s shell is the first thing consumers encounter and a better understanding of shell traits can provide an opportunity for product differentiation. The nature and inheritance of the shape and color of shells of the eastern oyster, Crassostrea virginica, remain largely unstudied. This thesis provides direct evidence that both traits have a strong genetic component in this species. In the first chapter, the ‘curl-back’ hinge abnormality is addressed. Two cohorts of oysters selected for ‘curl-back’ and for ‘flat’ hinges were produced and the progeny from each of the two crosses were grown separately in a common garden experiment. In the following year, crosses were repeated using selected F1s, resulting in two generations of selection for ‘flat’ and for ‘curled-back’ oysters. Four and eleven-month-old F2s from each cohort were subsequently cut ventro-dorsally and the relative curvatures of right and left valves were compared using either relative ratios of basic measurements or following a theoretical morphologic approach. Utilizing three independent methodologies, the curl-back shell abnormality is demonstrated to hae a strong genetic component in the eastern oyster.The second chapter examines the modes of inheritance of color morphs in the eastern oyster. Although, color morphs have been described in other species, such as the Pacific oyster, Crassostrea gigas, to date, no studies have been reported in C. virginica. To better understand the nature of shell pigmentation in this species, four color morphs were described and crossed. The proportions of color morphs in the progeny indicate that color and pattern are under genetic control and that their inheritance involves a small number of genes.The third and final chapter describes a comparative transcriptome study conducted in order to identify differentially expressed genes between dark and light regions of mantle tissue that correspond to shell pattens. Several genes were found to be differentially expressed, indicating a few gene families or pathways underlying the molecular basis of pigmentation that provides valuable insight for future investigations. |
