Adaptive significance of temperature-induced egg size plasticity in a planktonic rotifer, Brachionus calyciflorus

Larger egg size and body size at lower temperature are widely observed in zooplankton and other groups. Theoretically, considering the increased cost of producing larger eggs, females would produce larger and fewer eggs only if the newborn from such eggs perform better under certain environmental constraints, such as low temperature. In temperate lakes, low water temperature is a fairly reliable cue of future declining dietary conditions for herbivorous zooplankters. Under these conditions, females that produce more resistant offspring are likely to be selected. Nevertheless, it is not efficient for them to do this at high temperature, when the dietary conditions are usually more abundant. In this study, the adaptive significance of temperature-induced plasticity in a planktonic rotifer, Brachionus calyciflorus, was investigated. We found that: first, the egg size and body size were negatively related to temperature; second, neonates from larger eggs induced by low a temperature of 13°C were more resistant to starvation at three different experimental temperatures; third, life table experiments showed that offspring from larger eggs had a higher population growth rate and shorter juvenile period than those from smaller ones at low temperature, and vice versa, which suggests that this may be attributed to some form of anticipatory maternal effect. These differences in population growth rates were mainly due to higher fertility during the first 1 or 2 days after maturation. All of these findings support the view that temperature-induced egg size plasticity has adaptive significance in rotifers.