Life history of rotifers under temporally heterogeneous dietary sterol conditions

Herbivorous zooplankton potentially encounter temporal dietary heterogeneity in sterol, an essential group of lipids, over short or long time scales. There are a few studies showing that dietary sterol fluctuation will impact the short-term growth and reproduction of zooplankton, but life histories in response to dietary sterol fluctuation have not been studied. In this study, both short-term physical performances and life tables of the brackish rotifer Brachionus plicatilis were compared at a series of constant dietary cholesterol levels and under a diurnal switching-quality regime (SQ) between low-cholesterol (LQ) and high-cholesterol (HQ) diets. The ingestion rate, short-term reproduction rate and lifetime fecundity were correlated significantly with dietary cholesterol concentration in the Michaelis‒Menten function pattern. The short-term reproduction rate and lifetime fecundity were higher in the SQ treatment than in the nonlinear averaging prediction. Generally, rotifers under the SQ condition exhibited life history traits comparable to those groups under the medium and high cholesterol conditions, as did the cholesterol accumulation in mother rotifers. The maternal allocation of cholesterol per offspring, nevertheless, varied among different food regimes, and the SQ offspring had a higher sterol content than the HQ offspring. It is suggested that diurnal switching dietary cholesterol quality will not decrease the physiological performance of rotifers, unlike predictions based on the nonlinear averaging hypothesis, and the population can maintain their development under diurnal fluctuating dietary sterol conditions. Furthermore, the variable per offspring sterol investment may bear adaptive significance for rotifers under the fluctuating food environments.