Hypoxia and starvation tolerance in individuals from a riverine and a lacustrine population of Darwinula stevensoni (Crustacea: Ostracoda)

Abstract

High rates of survival of Darwinula stevensoni individuals at very low oxygen concentration were observed in a 768 hour laboratory experiment. Organisms from two different habitats (a river and a lake) whose populations were previously shown to be genetically different were used. No difference in hypoxia tolerance was found between individuals from the two habitats. Controls (kept in normoxic conditions and under starvation to match the experimental conditions - food addition would have altered the experiment's oxygen concentrations) had lower survival rates than treated organisms. Within controls, lower rates of survival were found in individuals from the lake than from the river. In a post experiment recovery period (768 hours) we found high survival in treated organisms, an indication of no permanent damage from hypoxia. No difference in survival was found between treated individuals from the lake and the river. Controls that survived starvation in normoxic conditions had lower survival rates than treated organisms. Controls from the lake suffered higher mortality than the ones from the river. Metabolic rate was evaluated by counting the number of respiratory plate beats per minute (Bpm) and the number of eggs produced. Before the beginning of the experiments, river individuals had lower Bpm than lake ones, suggesting a possible correlation with a higher starvation tolerance by riverine populations. Short hypoxia periods induced higher Bpm. A stable minimum was reached after 48 hour exposure to hypoxia. In the later part of the recovery phase Bpm stabilised at a value higher than that observed before the experiment, apparently the only sign of a significant hypoxia effect. Egg production continued, although at a reduced rate, under hypoxia and in the recovery phase.