Combined effects of temperature, food (Chlorella vulgaris) concentration and predation (Asplanchna girodi) on the morphology of Brachionus havanaensis (Rotifera)

Abstract

The combined effect of temperature, food level and the presence of an invertebrate predator on the body size of the rotifer Brachionus havanaensis were tested in this study. B. havanaensis was cultured at 15, 20, and 25°C under three different Chlorella vulgaris levels (0.5 × 106, 1.0 × 106 and 2.0 × 106 cells ml−1) in the presence and in the absence of Asplanchna girodi. For each treatment we maintained three replicates and constant (0.4 ind ml−1) population density of B. havanaensis. In treatments containing A. girodi, the predator was separated from the prey by a mesh (pore size 50 μm). On the last day of the experiment, a portion of the B. havanaensis population was sampled for several morphometric measurements (adult lorica length, width, posterior spine length, body volume, and the egg volume). Size measurements were done by drawing the specimens using a calibrated camera lucida. Statistically significant impact of temperature as well as the predator’s presence was observed on the lorica length, posterior spine, and egg volume of B. havanaensis. The interactions of food × temperature, or predator´s presence × food × temperature were non-significant (P > 0.05) for lorica length, spine length, body volume, and egg volume. Regardless of the type of treatment, there was a direct positive correlation between lorica length and width. Egg volume was linearly related to the adult size. Notably long posterior spines were observed in treatments containing the presence of A. girodi.