The physiological and anatomical responses toelevated temperature and zinc oxide exposure in Daphniamagna

Abstract

Global warming is an important current issue which increases the world�s temperature. Elevated temperature affects the toxic of heavy metals in aquatic ecosystems. Zinc oxide (ZnO) is a heavy metal compound that has been utilized in many industries, therefore ZnO may contaminate in wastewater and be released to freshwater ecosystems unavoidably. Here, we aim to investigate the combined effects of ZnO exposure and elevated temperature on life history traits, oxidative stress, energy reserves, and their related gene expressions in Daphnia magna. The results revealed that elevated temperature and ZnO exposure reduced growth, induced oxidative stress by altering superoxide dismutase activity and increasing malondialdehyde levels, and reduced energy reserves (carbohydrate, protein, and lipid) in D. magna. Moreover, expressions of related genes were altered. For example, the expression of growth-related gene, VEGFA, was significantly reduced in D. magna subjected to ZnO and elevated temperature. Fluctuations of detoxification related genes, Cyp360a8 and Mn-SOD, were observed by treated with both ZnO and elevated temperature. Expressions of energy-associated genes (FABP3, Ltb4dh, and Lip) were changed by ZnO exposure and elevated temperature in D. magna. Reproductive performance was inhibited and delayed maturity. The total number of first brood offspring and their size were decreased because of the ovarian developmental impairment after ZnO exposure under heat stress. Furthermore, anomalies in embryos were significantly induced, such as a deformed eye and the impaired antenna and/or a tail spine. In addition, the expressions of reproduction-related genes (EcR, vtg and VMO1) were decreased but the expressions of hypoxia- (HIF? and HIF?), heat stress- (hsp90), molting- (cut) and male induction- (dmrt93b) related genes were increased in D. magna subjected to ZnO and elevated temperature. Our results indicated that a combination of ZnO and heat stress induced the excessive ROS production leading to increase of oxidative stress, therefore, energy was reallocated to maintain physiological processes for detoxification and homeostasis instead of growth and reproduction. Moreover, the integrated biological value indicated the higher toxicity of ZnO under elevated temperature. Therefore, this study could clarify the changes in different levels of biological organization in freshwater zooplankton, D. magna. This will be useful for further studies to observe environmental change using D. magna on other zooplanktons as the bioindicators in freshwater ecosystem.

????????????????????????????????????????????????????????????? ????????????????????????????????????????????????????????????????? ??????????????????????????????????????????????????????????? ?????? ?????????????? ??????????????????????????????????????????????????????????????? ??????????????????????? ??????????????????????????????????????????????????????????????????????????????????? ????????????????? ???????????????????? ?????????????????? ???????????? ??????????????????????????????????????? ?????? Daphnia magna???????????????????????????? ????????????????????????????????????????????????? ?????????????????????????????? ???????????????????? (???????????? ?????? ????????) ???????????????????????????? ?????????????????????????????????? superoxide dismutase ????????????? malondialdehyde ?? D. magna ??????????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????? (VEGFA) ????????????????? (FABP3, Ltb4dh ??? Lip) ??????????????????? ????????? ???????????????????????????????????????????????????????? (Cyp360a8 ??? Mn-SOD) ?? D. magna ????????????????????????????????????????????? ????????????????????????????? ???????????????????????????? D. magna ?????????? ???? ???????????????????????????????????? ??????????????????????????????????????? ????????????????????????????????????????????????????????????????????????? ???? ??????????? ??????????????????? ???????????????????????????????????????????????????????? ????????????????????????????????????????????????????????????????????????? (EcR, vtg ??? VMO1) ??????? ??????????????????????????????????????????????????- (HIF? and HIF?) ??????????????????????????? (hsp90) ?????????? (cut) ????????????????????????????? (dmrt93b) ??????????????? D. magna ??????????????????????????????????????????????????????? ???????????????????? ????? ????????????????????????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????? ??????? ??????????????????????????????????????????????????????????????????????????????????????????? ??????????????????????????????????? ????????? ?????????????????????????????? (Integrated Biological Response) ??????????????????????????????????????????????????????????????????????????????????????? ???????????????????????????????????????????????????? ??? ????? ?????? D. magna ?????????????????????????????????????????????????????????????????????????????????????? D. magna ???????????????????????????????????????