Rapid evolution of phenoloxidase expression, a component of innate immune function, in a natural population of Daphnia magna

We show rapid microevolution of one component of invertebrate innate immunity, phenoloxidase activity, in a natural population of the water flea Daphnia magna. In Daphnia hatched out of different depths of a sediment core, levels of Daphnia phenoloxidase activity showed genetic variation and increased significantly in less than a decade. We discuss this increase in Daphnia immunity over time in the light of coinciding changes in predator and parasite environment. Together with earlier-found microevolutionary responses in stress protein expression of this Daphnia population, we find simultaneous changes of different defense systems in response towards multiple enemies.