Effects of food concentration on the life table demography and morphology of three Keratella quadrata morphotypes

Keratella quadrata with two (2PS), one (1PS) and none posteolateral (0PS) spines were cultured under four food levels (0.75 × 10 6 , 1.5 × 10 6 , 3.0 × 10 6 and 6.0 × 10 6  cells·mL −1 of Scenedesmus obliquus ) to test the differences in the life table demography and the morphological characteristics among these three morphotypes. The results showed that each K. quadrata morphotype could produce 2PS, 1PS and 0PS offsprings. The frequencies of 0PS were extremely low ( K. quadrata might be an abnormal development. Along with the elevating food concentration, 1PS morphotype reproduced more 2PS offsprings, suggesting that high energy input might be helpful to grow more posterolateral spines. However, in response to the increasing food concentration, 0PS rotifers produced more 1PS offsprings. The underlying mechanisms required further investigations. The posterolateral spine length of offsprings of 0PS K. quadrata was significantly longer than those of 2PS and 1PS rotifer parents at the four food concentrations, which probably help the offsprings of 0PS rotifer parents to survive in natural environments, since long and more posterolateral spines offer rotifers high ability to compete with other rotifers and cladocerans for food or to resist predators.