Effect of cadmium and ration level on oxygen consumption, RNA concentration and RNA-DNA ratio in two clones of Daphnia magna Straus

The rate of oxygen consumption, or respiration rate, of Daphnia magna is elevated as the food concentration of its environment increases, a phenomenon referred to as specific dynamic action (SDA). A possible cause of this response, the cost of tissue synthesis, was investigated using RNA concentration and RNA-DNA ratio as indices. The effects of cadmium on SDA was studied, to establish whether toxicants affect SDA either by increasing the rate of protein synthesis (for the repair/replacement of stress-damaged proteins), and/or by reducing feeding rate. Using two different genotypes, previously shown to differ in their sensitivities to cadmium, the possibility of genetic variation in response was also addressed.