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

The planktonic rotifer Brachionus calyciflorus was reported to have a behavioral response to the predatory rotifer Asplanchna, where individuals move up to a surface-film refuge. Here, I re-examine this response and also test the hypothesis that Asplanchna affects the propensity of B. calyciflorus to attach to glass surfaces. In eight experiments where B. calyciflorus was exposed to a strong Asplanchna stimulus for periods varying from 3 to 65 h, adults and juveniles showed no increase in propensity to settle at the surface film or to attach to glass surfaces. In treatments with and without Asplanchna, percentages of Brachionus free-swimming, attached to glass or settled at the surface film were 81–100%, 0–18% and 0–3%, respectively. Three types of defensive responses in planktonic rotifers are reviewed: (1) transgenerational, spine-development responses to the Asplanchna kairomone in many brachionids; (2) slow-onset (4–48 h) increases in attachment propensity due to Asplanchna, or just its kairomone, in the facultatively epizoic Brachionus rubens and Brachionus variabilis and in an attachment-prone clone of Brachionus dorcas (B. calyciflorus species complex) and (3) brief escape movements caused by disturbance immediately after contact or near-contact with various predators (Asplanchna, Daphnia, copepods) in Filinia, Keratella, Hexarthra and Polyarthra.