A model for the maintenance of genetic variability and its utilization in genetic improvement of oyster populations

Abstract

A large amount of variability for size is observed in oysters of the same age. A model is proposed for the maintenance of this variability in the population. It recognizes that: (1) growth rate has a strong genetic component; (2) the ability of an oyster to breed is a function of its size and not age; (3) most oysters are harvested and eliminated from the breeding population once they reach market size; and (4) there is a continuous mortality in the population. The time taken for oysters to reach spawning and harvesting sizes depends on the growth rate, and these thresholds for fast-growing and slow-growing individuals are realized at different times. Therefore, the breeding population has to meet to meet two balancing restrictions and, in doing so, allows the fast- and slow-growing sub-populations to release gametes in equilibrium and maintain the variability generation after generation. The genetic improvement of a population by increasing growth could be achieved by using the model to eliminate slow-growing individuals at the right time. Selection for fast-growing oysters could also be accomplished by selecting fast-growing larvae that settle early, which may be particularly applicable in the hatcheries.