The importance of calcium in improving resistance of Daphnia to Microcystis.

Changing environmental calcium (Ca) and rising cyanobacterial blooms in lake habitats could strongly reduce Daphnia growth and survival. Here, we assessed the effects of maternal Ca in Daphnia on transfer of resistance to their offspring against Microcystis aeruginosa PCC7806 (M. aeruginosa). Laboratory microcosm experiments were performed to examine effects in Daphnia carinata (D. carinata) and Daphnia pulex (D. pulex), and that how Ca induce responses in their offspring. The results showed that growth and survival were increased in offspring from exposed Daphnia as compared to unexposed, when raised in high Ca and increasing M. aeruginosa concentration. Among exposed Daphnia, offspring from high Ca mothers, produced more neonates with large size and higher survival as compared to offspring from low maternal Ca. Exposed D. carinata and D. pulex offspring, when reared in Ca deficient medium and increasing M. aeruginosa concentration, time to first brood increased, size become large and total offspring decreased subsequently in three alternative broods in offspring from low maternal Ca. In contrast, growth and reproduction in offspring from high Ca exposed mothers were consistent in three alternative broods. Despite species specific responses in growth, survival and variant life history traits in two Daphnia species, our results not only show maternal induction in Daphnia but also highlight that offspring response to M. aeruginosa varies with maternal Ca. This study demonstrates that Ca have role in Daphnia maternal induction against Microcystis, and recent Ca decline and increasing Microcystis concentration in lakes may decrease Daphnia growth and survival. Our data provide insights into the interactive effect of maternal Ca and Microcystis exposure on Daphnia and their outcome on offspring life history traits and survival.