BARKAUSKAS, R.T.*; SPARKES, T.C.: Effects of abiotic and biotic stresses on patterns of energy storage and use in two species of crustacean: Gammarus pseudolimnaeus and Caecidotea intermedius.

Effective energy budget management by an organism will influence its ability to tolerate both abiotic and biotic stress; however, except in birds little is known about the potential for patterns of energy storage and use to be adaptive in natural populations. We used a laboratory-based experiment to examine the effects of an abiotic (oxygen concentration) and biotic (predation risk) stress on the pattern of energy storage and use in two species of crustacean (Gammarus pseudolimnaeus and Caecidotea intermedius). These species provide a useful comparison because isopods are more tolerant to stress than amphipods. We placed juvenile amphipods and isopods into containers that had a shelter and leaf disks. We had a total of eight treatments and twenty replicates: species type (amphipod, isopod), oxygen level (high, low), and predation risk (fish cue present, absent). Every morning for five weeks water from tanks containing fish or no fish was added to appropriate containers and leaf disks were replenished. Data on overall distribution patterns of the organisms were collected using spot checks on alternate days. Oxygen data were also collected using a dissolved oxygen probe. At the end of five weeks the organisms were frozen and will be biochemically analyzed for glycogen content. The results will be presented with reference to species differences in responses to abiotic and biotic stress and its importance to variation in stress tolerance in nature.