Application of a Gene-Based Population Dynamics Model to the Optimal Egg Size Problem: Why Do Bivalve Planktotrophic Eggs Vary in Size?

Abstract

ABSTRACT The presumption is that egg quality influences larval survival and that egg size influences egg quality. Thus, larger eggs should be favored by selection. Counterweighing the tendency for egg size to increase is the number of eggs that can be produced if egg size remains small. We examine how egg size and egg number counterbalance in Crassostrea oysters, resulting in an average egg size near 50 µm. Simulations imposing a diversity of ranges in larval survivorship—from little advantage for large eggs relative to small eggs to a great advantage—yield some anticipated outcomes in which genotypes generating larger eggs are favored. In other simulations, however, genotypes generating smaller eggs became increasingly common. In these cases, egg size declines, as does the likelihood of survival of individual larvae: the antithesis of expectation. Few simulations identify preferred egg sizes near the size typically observed, suggesting that, under most field conditions, a selective advantage exists for s...