Flexible energy allocation in zebra mussels (Dreissena polymorpha) in response to different environmental conditions

The ability to adjust physiological parameters in response to environmental conditions while simultaneously maintaining growth and reproduction increa ses an organism's fitness. We altered energy demands to examine the effect of environmental conditions on energy allocation in zebra mussels (Dreissen a polymorpha). We manipulated metabolic costs and ingestion with combinatio ns of 4 temperatures (12, 18, 24, and 30 degreesC), 3 rations, and 2 diet q ualities for 7 wk in laboratory experiments. We measured maintenance costs (oxygen consumption and ammonia excretion), somatic tissue mass, shell grow th, and reproduction to determine if zebra mussels have flexible energy all ocation into tissue mass and reproduction. Increased temperature and ration increased metabolic costs but diet qualities did not. Assimilation efficie ncy, higher in good diet than poor, decreased with ration. Shell growth, ti ssue mass, and reproduction responded similarly to temperature and ration. Reproduction was similar, whereas growth and survival differed the most bet ween diets. Good diet mussels reproduced, maintained tissue mass, grew, and survived. Poor diet mussels reproduced but did not grow and died. Diet qua lity influenced reproductive effort, with lower investment in body mass in the poor diet yielding higher reproductive effort. Thus, zebra mussels are flexible in energy allocation and in stressful conditions, most importantly reduced food quality; reproduce at the expense of maintenance thereby incr easing the probability of death.