How does protandry help hermaphroditic animals avoid self-fertilization?

Protandry is a reproductive strategy in hermaphroditic animals where an individual develops male reproductive organs or matures its sperm before developing female organs or producing eggs.1

By ensuring that the male and female phases of the growth cycle occur at different times, the animal effectively prevents self-fertilization. This temporal separation means that when an individual is functionally male, it cannot fertilize itself because it lacks mature eggs, and when it is functionally female, it no longer produces sperm.12

This mechanism allows hermaphroditic species to maintain the benefits of cross-fertilization—such as the reassortment and recombination of genes—even though they possess both sets of reproductive organs. For example, certain shrimps function as males while young and smaller, then transition into females as they reach full growth, ensuring they mate with individuals of a different generation or developmental stage.2