Consuming Heat acclimated Algae improves Heat Tolerance and Longevity in Daphnia
Location
D.P. Culp Center Room 303
Start Date
4-5-2024 2:30 PM
End Date
4-5-2024 3:30 PM
Name of Project's Faculty Sponsor
Lev Yampolsky
Faculty Sponsor's Department
Biological Sciences
Competition Type
Competitive
Type
Oral Presentation
Presentation Category
Science, Technology and Engineering
Abstract or Artist's Statement
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<0.0001). Similarly, Daphnia kept in 20℃ and fed with heat-stressed (25℃-grown) algae had a significantly higher heat tolerance compared to their counterparts fed the two other diets (p<0.0001). This effect included both increased time until immobilization and the frequency of individuals retaining heartbeat after 1 hour when exposed to 37 ℃. These results indicate that consuming heat-acclimated algae facilitates the physiological heat acclimation. In the longevity experiment, the cohort consuming 25℃-grown food had significantly higher longevity compared to the group consuming 12℃ foods (p<0.0001). We hypothesize that heat stressed algae have lower amounts of PUFAs and thus lower levels of lipid peroxidation (LPO), leading to greater acute heat tolerance and longevity. For this purpose, we are currently conducting LPO and total antioxidant measurements which would be followed by a transcriptomics analysis to explain gene expression differences. Overall, this is the first work to investigate the impact of heat acclimated algae on improving physiological adaptation in Daphnia and will provide a mechanistic explanation of these results to shed light on xenohormesis.
Consuming Heat acclimated Algae improves Heat Tolerance and Longevity in Daphnia
D.P. Culp Center Room 303
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<0.0001). Similarly, Daphnia kept in 20℃ and fed with heat-stressed (25℃-grown) algae had a significantly higher heat tolerance compared to their counterparts fed the two other diets (p<0.0001). This effect included both increased time until immobilization and the frequency of individuals retaining heartbeat after 1 hour when exposed to 37 ℃. These results indicate that consuming heat-acclimated algae facilitates the physiological heat acclimation. In the longevity experiment, the cohort consuming 25℃-grown food had significantly higher longevity compared to the group consuming 12℃ foods (p<0.0001). We hypothesize that heat stressed algae have lower amounts of PUFAs and thus lower levels of lipid peroxidation (LPO), leading to greater acute heat tolerance and longevity. For this purpose, we are currently conducting LPO and total antioxidant measurements which would be followed by a transcriptomics analysis to explain gene expression differences. Overall, this is the first work to investigate the impact of heat acclimated algae on improving physiological adaptation in Daphnia and will provide a mechanistic explanation of these results to shed light on xenohormesis.