Honors Program

Midway Honors

Date of Award

5-2016

Thesis Professor(s)

Lev Yampolsky

Thesis Professor Department

Biological Sciences

Thesis Reader(s)

Alesky Vasiliev, Thomas Laughlin, Aruna Kilaru

Abstract

The aquatic zooplankton crustacean Daphnia magna must be able to tolerate thermal stress in order to survive their native shallow ponds that are susceptible to drastic seasonal and diurnal temperature fluctuations as well as to globally increasing temperatures. Survival in such variable environments requires plastic responses that must include fundamental aspects of Daphnia biochemistry and physiology. Adaptive response to selection favoring such plastic phenotypes requires the presence of genetic variation for plastic response in natural populations. Adverse effects of elevated temperature on aquatic organisms are diverse and so are their plastic responses; among the most severe challenges aquatic organisms face when exposed to heat is the elevated oxidative stress. In this work we focused on short-term and long-term responses of Daphnia to temperature changes that increase its resistance to oxidative stress.

Daphnia acclimated to stressful but non-lethal temperature (28ºC) show longer survive during exposure to a lethal temperature (37ºC) than those acclimated to the optimal temperature (18ºC). Short-term reciprocal switches between 18ºC and 28ºC result in intermediate temperature tolerance. These changes are accompanied by mirroring changes in total antioxidant capacity indicating the increased antioxidant capacity as a possible causative mechanism for heat tolerance gained from acclimation.

The analysis of 6 geographically distinct genotypes representing a range of temperature tolerance levels shows a genetic difference in response to short-term and long-term acclimation as well as in the effect of antioxidant capacity on temperature tolerance. These results indicate a significant degree of local adaptation in heat and oxidative stress defenses in Daphnia and provide a better understanding of adaptive responses of this zooplankton crustacean to rising temperatures.

Publisher

East Tennessee State University

Document Type

Honors Thesis - Open Access

Copyright

Copyright by the authors.

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