9601069 Latz In the midwater depths of the ocean, the largest habitat on earth, there are few refuges from predation. Some animals have evolved an extraordinary anti-predation behavior using bioluminescent countershading to help them remain cryptic to visual predators. This strategy, called counterillumination, involves the biological production of dim light from the ventral surface of many fishes, squids, and shrimps in order to disrupt their silhouette. As yet Dr. Latz does not have a comprehensive understanding of the physiological pathways that regulate how vision mediates the production of bioluminescence for countershading. In the midwater penaeid shrimp Sergestes similis, a common member of the midwater community off the west coast of the U.S., the interaction of both hormonal and neural systems may be involved in the control of counterillumination. The goal of the present study is to obtain pilot data from which to develop a model for the physiological control of luminescent countershading behavior in Sergestes similis. His previous work has demonstrated that S. similis is a stable laboratory preparation; it counterilluminates in response to downward-directed illumination, detected by the eyes, with light emission from five light organs that are modified portions of the hepatopancreas (liver). Dr. Latz has suggested that two control systems, one hormonal and the other neural, regulate the induction and control of counterillumination. In the present study the following hypotheses will be addressed: (1) the induction of bioluminescence involves a hormonal pathway, (2) a hormone which helps regulate the intensity sensitivity of the eye is responsible for the induction of bioluminescence, so that (3) the induction of bioluminescence is linked to light adaptation of the eye, and (4) once induced, the control of counterillumination involves a neural pathway. The main area of study will identify the physiological mechanisms controlling light emission. Tests using extracts of the eyestalk s and purified hormones will determine whether a hormonal component is involved in bioluminescence induction, and if so, identity the hormone. Bioluminescence will be used as a behavioral assay of the color and intensity sensitivity of the eye. Collaborative work will compare the sensitivity of the photoreceptors with behavioral tests of visual sensitivity. The importance of studying the physiological mechanisms of bioluminescence in Sergestes similis extends beyond understanding how midwater animals control luminescent countershading behavior. If a hormone is involved, this would be the first documentation of hormonal control of bioluminescence in any animal, and a significant contribution to the field of endocrinology by identifying an entirely new target system. Because counterilluminating animals directly respond to their optical environment, an understanding of the control of bioluminescence also provides an insight into the poorly understood vision of deep-sea animals. Overall, this study will be a major contribution toward understanding the physiological control of bioluminescence, one of the most widespread yet enigmatic behaviors in the ocean.