Does the predatory rotifer Asplanchna induce a behavioral response in the prey rotifer Brachionus calyciflorus?

This article investigates the behavioral response of the planktonic rotifer *Brachionus calyciflorus* to the predatory rotifer *Asplanchna brightwellii*, specifically testing whether exposure to *Asplanchna* or its kairomone influences *B. calyciflorus*’ propensity to attach to glass surfaces or settle at the water’s surface film. Across eight experiments with exposure durations ranging from 3 to 65 hours, neither adult nor juvenile *B. calyciflorus* showed increased attachment or surface-settling behavior in response to *Asplanchna* stimuli. The study contrasts these findings with previous reports of behavioral defenses in other *Brachionus* species and clones, as well as a "floating" response observed in a Chinese clone of *B. calyciflorus*, suggesting possible clonal or species-complex differences. It also reviews three known types of rotifer defensive responses to predators: (1) transgenerational morphological spine development induced by *Asplanchna* kairomones, (2) slow-onset increases in attachment behavior in certain facultatively epizoic *Brachionus* species, and (3) rapid escape movements triggered by hydromechanical disturbance in other rotifer genera. The study concludes that the Florida strain of *B. calyciflorus* examined lacks an *Asplanchna*-induced behavioral attachment defense, relying instead on morphological defenses.