The effect of environmental stress on absolute and mass-specific scope for growth in Daphnia magna Strauss.
Daphnids were reared for 2 weeks in different concentrations of food or cadmium, and growth and reproduction were measured as endpoints. At the end of the 14-day experimental period, scope for growth (SFG) was measured and expressed per individual (mJ/ind/h=absolute SFG) and per mg dry weight (mJ/mg/h=mass-specific SFG). Both food deprivation and cadmium stress decreased body size, and absolute SFG decreased with decreasing body size in both exposure scenarios. Also mass-specific SFG decreased with decreasing body size under cadmium exposure, but an increase in mass-specific SFG was observed in the food ration experiment. This suggested that cadmium stress, apart from decreasing energy assimilation, also disturbs energy metabolism. Changes in both absolute and mass-specific SFG were mainly determined by changes in energy uptake, whereas energy loss varied little in response to both environmental stressors. With the cadmium-stressed daphnids, reproduction correlated positively with both absolute and mass-specific SFG. With the food-stressed daphnids however, reproduction correlated positively with absolute SFG but negatively with mass-specific SFG. Mass-corrected SFG still decreased with increasing cadmium stress, but did not differ between ration groups. Thus, mass-corrected SFG provides an indication of metabolic functioning, but appears less suited as an indicator of reproduction.
Baillieul
Marc
M
University of Antwerp, Ecophysiology, Biochemistry, and Toxicology Group, Department of Biology, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
Smolders
Roel
R
Blust
Ronny
R
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002478:Cells, Cultured; D003621:Daphnia / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D004435:Eating; D004777:Environment; D012098:Reproduction / Q000187:drug effects / Q000502:physiology; D013312:Stress, Physiological / Q000503:physiopathology*
D002104:Cadmium