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Here, we report on experiments to determine the effects of sub-lethal concentrations of cadmium (Cd) as CdCl2 (0.05, 0.1, and 0.2 mg L−1) on the life history parameters of Brachionus calyciflorus cultured under two temperature regimes: variable (20–30°C diurnal cycle) and constant (20, 25, or 30°C). Temperature and mode of exposure affected the demographic responses of B. calyciflorus. In general, for B. calyciflorus cultured under constant temperatures and exposed to CdCl2 the life history variables were more adversely affected than those under the variable temperature regime. Age-specific reproductive output by B. calyciflorus exposed to different temperature regimes under different concentrations of CdCl2 showed a general pattern of increase in offspring production with increasing age of the cohort for the first 10 days and thereafter declined rapidly. Depending on the temperature regime and Cd concentration, average lifespan, gross reproductive rate, net reproductive rate, generation time, and rate of population increase per day varied from 5 to 8 days, 10 to 38 offspring female−1, 5 to 16 offspring female−1, 3 to 5 days, and 0.4 to 1.4 day−1, respectively. In the absence of the heavy metal, average lifespan and gross and net reproductive rates decreased with increase in fixed temperature range, while generation time and the rate of population increase showed no clear trend with constant temperature regimes. The effect of Cd concentration on life history parameters of B. calyciflorus was generally more severe at extreme temperatures (20 or 30°C) as compared to the fluctuating temperature regime. These results have important implications for aquatic toxicology testing protocols. |
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