Behaviors Producing Photodispersal in Stentor coeruleus¶

Photo-dependent population dynamics of Stentor coeruleus and its consumption of Colpidium striatum

The predatory protozoan Stentor coeruleus Ehrenberg, 1830 is known to show photosensitivity and photodispersion, avoiding regions of high light intensity as an antipredation strategy. This physiological and behavioral response to light likely has demographic consequences. We manipulated light intensity to determine population responses of S. coeruleus and the resulting effects on its prey Colpidium striatum Stokes, 1886. We show that S. coeruleus maintained the highest population density under ambient light levels and low densities under both high and no light treatments. The results from the no light treatment were surprising because little work has been done on possible important behavioral and physiological processes cued by light. These results add power to the use of S. coeruleus as a model predator system to test ecological dynamics and processes associated with predation.

Photosensory transduction in unicellular eukaryotes: A comparison between related ciliates Blepharisma japonicum and Stentor coeruleus and photoreceptor cells of higher organisms

Blepharisma japonicum and Stentor coeruleus are related ciliates, conspicuous by their photosensitivity. They are capable of avoiding illuminated areas in the surrounding medium, gathering exclusively in most shaded places (photodispersal). Such behaviour results mainly from motile photophobic response occurring in ciliates. This light-avoiding response is observed during a relatively rapid increase in illumination intensity (light stimulus) and consists of cessation of cell movement, a period of backward movement (ciliary reversal), followed by a forward swimming, usually in a new direction. The photosensitivity of ciliates is ascribed to their photoreceptor system, composed of pigment granules, containing the endogenous photoreceptor -- blepharismin in Blepharisma japonicum, and stentorin in Stentor coeruleus. A light stimulus, applied to both ciliates activates specific stimulus transduction processes leading to the electrical changes at the plasma membrane, correlated with a ciliary reversal during photophobic response. These data indicate that both ciliates Blepharisma japonicum and Stentor coeruleus, the lower eukaryotes, are capable of transducing the perceived light stimuli in a manner taking place in some photoreceptor cells of higher eukaryotes. Similarities and differences concerning particular stages of light transduction in eukaryotes at different evolutional levels are discussed in this article.