Bioluminescence and color change in Euphausia pacifica
Date
1979
Authors
Harvey, Brian J.
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Abstract
Some of the morphological, physiological and biochemical characteristics of the photophores of the euphausiid shrimp Euphausia pacifica are examined. Electron micrographs of the light organ show that the 'rod mass', or light-emitting zone, is composed of a highly ordered crystalline substance in intimate contact with elements of the circulatory system, and that a sphincter system exists at the edge of this body, so situated as to control the irrigation of the area. The innervation of these sphincters is described, as are the dioptric, or light-directing, structures.
The phenomenon of Flash-Stimulated Inhibition (extinction of a luminescent display by strong light) is investigated in pinioned specimens stimulated to luminesce by the injection of 40 pg 5-HT. Records from whole animals and from ocular photophores alone are presented. Progressive isolation of the luminescing organ suggests that it may respond to light without the intervention of the central nervous system; studies with luminescing homogenates demonstrate that Flash Stimulated Inhibition can occur in vitro, and it is concluded that the phenomenon is not behaviourally significant.
Several characteristics of the luminescence system in vitro are investigated, including pH dependence and temperature optimum. A new cofactor, blood-borne and probably protein, is found to be essential to the light reaction.
The color change mechanism of E. pacifica is investigated. Red chromatophores of the integument, abdominal nerve cord and photophores are described, and their response to ambient light and to 5-HT is detailed. The behavioural implications of these findings are discussed.