Document Type


Publication Date


Publication Source

Journal of Plankton Research




Oxford University Press

Place of Publication

Oxford, UK

Peer Reviewed



Abstract----A strain of the green alga Oocystis isolated from a lake showed a decline in digestion defenses and an increase in growth rate over three years of culture. Changes over time were corroborated by comparisons between a substrain grown continuously in light and two substrains kept refrigerated in the dark most of the time. Continuous culture in light lead to a sharper decline in grazer defenses and an increase in growth rate. The decline in digestive defenses was evidenced by increases in carbon assimilation efficiency (AE) and juvenile growth rate of Daphnia feeding on the alga as well as decreases in the incidence and thickness of the alga's protective gelatinous sheath. Moreover, two strains of Oocystis from culture collections isolated decades earlier showed no evidence of grazer defenses in comparison to a high quality control alga. At high algal concentrations, Daphnia juvenile growth rate increased from 0.10 to 0.38 d-1 for field-isolated Oocystis over time in culture and ranged from 0.57-0.61 d-1 for the three undefended algae. Our experiments suggest that grazing favors the evolution of digestion defenses in Oocystis at the cost of slower growth and show that caution is needed when using cultured algae in food chain experiments.


phytoplankton evolution; cost of defense; defense versus growth trade-off; Daphnia


Biology | Ecology and Evolutionary Biology | Terrestrial and Aquatic Ecology