Heat Acclimated Algae Improves Heat Tolerance and Longevity in Daphnia

Xenohormesis suggests that consuming stressed food provides physiological adaptation to the consumer for similar stresses. To evaluate this, Daphnia magna was provided with heat-stressed Nannochloropsis limnetica grown at 25℃ whereas the control group was provided Nannochloropsis limnetica grown at 12℃. In the heat tolerance experiment, Daphnia kept at 28℃ and 20℃ while consuming 25℃ algae had significantly higher heat tolerance compared to the control. Additionally, in stressed conditions, Daphnia consuming 25℃-grown food had significantly higher lifespan compared to the control. Next, Daphnia consuming 25℃-grown algae had significantly higher levels of antioxidants which could explain the lifespan extension. Finally, in fatty acid analysis, eicosatetraenoic acid (EPA) was found lower in Daphnia consuming 25℃ cultures compared to Daphnia consuming 20℃ cultures. We speculate that this lower EPA level is increasing membrane rigidity and hence higher heat tolerance is observed. These findings indicate consumption of stressed algae might provide physiological benefits in Daphnia.