Effect of temperature on waterflea Daphnia magna (Crustacea:Cladocera)

Abstract

Acclimation of the waterflea Daphnia magna Straus (Crustacea: Cladocera) at 2 o to 12 o C above their habitat temperature (16 o C) for 6 months increased the rate of their metabolic activity (respiration and heartbeat rates). Temperature-enhanced activity appeared to be supported by cellular ATP synthesis (increased cytochrome c oxidase and succinic dehydrogenase activities) and hydrolysis (increased ATPases activities), indicating high rate of intermediary metabolism, the substrates for which may come from the stored glycogen and fat in addition to ingested food. Temperature-enhanced activity was associated with loss of body mass and decrease in body size, both of which may result from hyperactivity (causing lack of replenishment of consumed stored glycogen and fat) and loss of body water (due to hyperosmolarity of water because of evaporation). Hyperthermia-caused hypoxia was associated with increase in hemoglobin (Hb) synthesis (a typical daphnid response to hypoxia). These responses to hyperthermic stress started showing up after one month of acclimation at 27 o-29 o C and after 6 months at lower temperature ranges (18 o-20 o C) indicating the possibility of initiation of similar responses in field populations at current expected rise in global temperature due to climate change. Since the thermal stress will continue for generations, the effects observed with D. magna may start showing up in other small aquatic poikilotherms; indicating the speeding up of their life processes and of their gametes, embryos, larvae, and young adults. Such responses can affect aquatic ecosystem dynamics.