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Xenohormesis is the phenomenon where an animal acclimates to an environmental stress without being directly exposed to it, but by consuming food organisms that have been exposed to stress and therefore contain stress-response molecules such as antioxidants. However, the lack of mechanistic explanation of this phenomenon compelled us to design a project that aims to evaluate xenohormesis in a novel organism and understand its mechanism. Daphnia was selected as the model organism due to their short lifespan, well characterized genome, and genetic similarity with humans. Next, the algal food for this experiment was Nannochloropsis limnetica which is a freshwater alga and grows optimally at 10-20℃. The control treatment consisted of this alga grown at 12 ℃. We heat-stressed the algae by growing them either at 20 ℃ or at 25℃, which is, respectively, the upper limit of optimal zone and close to the upper tolerance limit for N. limnetica. Likewise, Daphnia were grown at either 12 ℃, or 20 ℃, or 28 ℃, with the 28 ℃ treatment being close to the upper tolerance limit, which also provides acclimation to heat resulting, hermetically, in higher tolerance to lethal temperature. To investigate the xenohormetic effects in acute heat tolerance and longevity experiments Daphnia kept at 12℃ and 28℃ were both provided with algae grown either in 12℃ or in 25℃, while Daphnia kept at 20℃ were provided with algae grown in either 12, or 20, or 25 ℃. To capture intraspecific variation, we conducted this experiment in four different clones of D. magna extracted from different geographic locations. In the acute heat tolerance experiment, Daphnia kept at 28℃ and provided algae grown in 25℃ had significantly higher heat tolerance compared to the Daphnia kept in the same temperature but consumed algae grown in 12℃ (p |
