Large-scale ciliary reversal mediates capture of individual algal prey by Müller’s larva

We documented capture of microalgal prey by several species of wild-caught Müller’s larvae of polyclad flatworm. To our knowledge, this is the first direct observation of feeding mechanism in this classical larval type. High-speed video recordings show that virtually all captures are mediated by large-scale transient ciliary reversal over one or more portions of the main ciliary band corresponding to individual lobes or tentacles. Local ciliary beat reversals alter near-field flow to suck parcels of food-containing water mouthward. Many capture episodes entail sufficient coordinated flow disruption that these compact-bodied larvae tumble dramatically. Similar behaviors were recorded in at least four distinct species, one of which corresponds to the ascidian-eating polyclad Pseudoceros.

Nociceptin Signaling Involves a Calcium-Based Depolarization in Tetrahymena thermophila

Tetrahymena thermophila are free-living, ciliated eukaryotes. Their behavioral response to stimuli is well characterized and easily observable, since cells swim toward chemoattractants and avoid chemorepellents. Chemoattractant responses involve increased swim speed or a decreased change in swim direction, while chemorepellent signaling involves ciliary reversal, which causes the organism to jerk back and forth, swim in small circles, or spin in an attempt to get away from the repellent. Many food sources, such as proteins, are chemoattractants for these organisms, while a variety of compounds are repellents. Repellents in nature are thought to come from the secretions of predators or from ruptured organisms, which may serve as “danger” signals. Interestingly, several peptides involved in vertebrate pain signaling are chemorepellents in Tetrahymena, including substances P, ACTH, PACAP, VIP, and nociceptin. Here, we characterize the response of Tetrahymena thermophila to three different isoforms of nociceptin. We find that G-protein inhibitors and tyrosine kinase inhibitors do not affect nociceptin avoidance. However, the calcium chelator, EGTA, and the SERCA calcium ATPase inhibitor, thapsigargin, both inhibit nociceptin avoidance, implicating calcium in avoidance. This result is confirmed by electrophysiology studies which show that 50 M nociceptin-NH2 causes a sustained depolarization of approximately 40 mV, which is eliminated by the addition of extracellular EGTA.

Ciliary reversal and locomotory control in the pluteus larva of Lytechinus pictus

Normal swimming behaviour of Lytechinus pictus larvae and the effects of selected drugs are described, based on direct observation and videotapes of free-swimming and tethered larvae. The principal effector response is a coordinated ciliary reversal that enables larvae to back away from obstacles and avoid entanglement. The effect is best seen in the epaulettes, whose large size makes the pluteus an especially favourable subject for behavioural observation and tests. Reversals and sustained arrests can be induced by various cholinergic agonists, notably nicotine, which is active to concentrations of 0.2 μM. Dopamine and adrenaline cause reversals and arrests as well, but they act initially on the response as a whole, increasing its frequency, rather than directly on ciliary beat. The data suggest a two-step control sequence, with an initial catecholamine-dependent step that triggers a cholinergic effector response.