Bioenergetics of a Semi-Tropical Cladoceran, Daphnia Iumholtzi

ABSTRACT

The bioenergetics of D. lumholtzi from Kentucky Lake U.S.A. was investigated across a wide range of temperatures (16–31 °C) and food concentrations. Ingestion and assimilation rates were measured using ¹⁴C as a tracer. Growth rate was observed in the laboratory at 23 °C with ambient food concentration from Kentucky Lake. Respiration rate and temperature dependence of respiratory enzymes was determined.

Between temperatures of 16 and 30 °C, ingestion ranged from 0.214 to 0.316 μg C hr⁻¹ and assimilation rate ranged from 0.084 to 0.181 μg C hr⁻¹. Assimilation efficiency averaged 56% across this temperature range with a food concentration of 0.69 mg C L⁻¹. Growth at 23 °C was described well by an empirical von Bertalanffy relationship and was quite rapid. Growth of neonate to first reproduction as adults was about six days. Release of offspring occurred on day 7 on the average, and clutch size ranged from 2 to 14. The magnitude of in situ respiration was in the range of that measured for other Daphnia species; however, the electron transport system measurement of cellular respiration indicated that optimal temperature for respiratory activities was several degrees higher than for both arctic and temperate Daphnia species. The energy budget of D lumholtzi as a function of temperature differed from published values for temperate region Daphnia species with the peak available energy (assimilation-respiration) for growth and reproduction occurring at the highest experimental temperature treatment (31 °C). This suggest a physiological adaptation to competitive ability under differing climatic conditions.