Resistance variation within a Daphnia pulex population against toxic cyanobacteria

Thirteen sympatric Daphnia pulex clones differed significantly in fitness when fed Chlorella pyrenoidosa and toxic Microcystis aeruginosa. The least susceptible clone was 12 times less susceptible to M. aeruginosa than the most susceptible clone. The correlations of D. pulex resistance with the slope and the mean of fitness reaction norms imply that both an increase in fitness for two diets and a reduced phenotypic plasticity contributed to the evolution of resistance to M. aeruginosa.