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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 637

John J. Gilbert and Kevin L. Kirk; Escape response of the rotifer Keratella: Description, stimulation, fluid dynamics, and ecological significance. Limnol.Oceanogr. 33(6, part 2):1440-1450, 1988

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Keratella spp. sometimes exhibited escape responses when being contacted or closely approached by the predatory rotifer Asplanchna brightwelli, when encountering the inhalant currents of the cladoceran competitor Daphnia, and when encountering a simple, calibrated, siphonal flow field mimicking that entering Daphnia. Escape responses in Keratella cochlearis and Keratella testudo were brief (~2 sec.), orthokinetic increases in swimming speed. Velocities rapidly (0.3-0.5 sec.) increased ~3.6-fold to a maximum (~1.8 mm/sec.) and then gradually declined to preresponse levels (~0.5 mm/sec.); displacements were ~2 mm or 12-18 body lengths. Velocity increases probably are mediated by increased beat frequencies of coronal locomotory cilia. The stimulus for response initiation in K. testudo probably is deformation (shear) of the rotifer itself of its surrounding medium and may be detected by internal or external mechanoreceptors. Threshold stimuli were associated with siphonal flow-field currents of 0.35 mm/sec. and Asplanchna flow-field currents of about 0.65 mm/sec. Escape-response initiation in K. testudo was more sensitive to siphonal flow stimuli than that in Polyarthra, suggesting a direct correlation between escape-response velocity and stimulus threshold. Escape responses in K. cochlearis and K. testudo to encounters with Asplanchna and Daphnia were always successful but were not always initiated. They reduced the probability of the rotifers being captured, and hence eaten or damaged, by these organisms 25-50%, Keratella's behavioral response complements its other, morphological defenses (size, integumentary skeleton, spination) and increases its ability to coexist with various invertebrate predators and interference competitors in natural zooplankton communities.