Effects of Chronic Hypoxic Exposure on Selected Temperature during Acute Normoxia, Hypoxia, and Inhibition of Oxidative Phosphorylation in the Protozoan Paramecium Caudatum
Bencic, David C.
Hypoxia (decreased availability of oxygen) elicits a variety of adaptive physiological and behavioral responses in both endotherms and ectotherms that either increase the supply of oxygen (02) or decrease the need for 02. An important behavioral response that decreases 02 need is hypothermia. Although hypoxia-induced hypothermia is important and widespread, little is known of the factors that influence it. This study investigated effects of chronic hypoxic exposure on this response in the protozoan Paramecium cauda tum. Specific hypotheses tested were: 1) Paramecia grown in a hypoxic environment would adapt and behaviorally maintain a higher mean selected temperature (Ts) during acute hypoxia than normoxic-cultured paramecia. 2) Hypoxiaadapted paramecia would have a higher Ts after addition of sodium azide (NaN3) because adaptation to hypoxia involves an increase of capacity for anaerobic respiration. Paramecia were cultured in normoxic and hypoxic environments and isolated during mid-log phase growth. The paramecia were placed in an aquatic thermal gradient and recorded using video microscopy. The Ts was determined after exposure to acute normoxia, hypoxia, and after addition of NaN3, an inhibitor of oxidative phosphorylation. Under normoxic conditons, no significant difference existed between the Ts of paramecia cultured in normoxia and hypoxia, however; hypoxia-cultured paramecia were able to successfully adapt to hypoxia and thus maintained a significantly higher Ts during acute hypoxia than normoxic paramecia. Additionally, in the presence of NaN3, hypoxia-adapted paramecia had a significantly higher Ts than the normoxic paramecia, suggesting that the mechanism of adaptation may be an increased ability for anaerobic respiration.
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