The structure and sensitivity of the eye of different life history stages of the ontogenetic migrator Gnathophausia ingens
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The structure and ultrastructure of the photoreceptors of several life history stages of the ontogenetically migrating lophogastrid crustacean Gnathophausia ingens were examined. The younger instars of this species live in a much brighter light field than the older instars, and this difference is reflected in differences in their visual systems. The shallowest free living individuals (instars 3 and 4) possess a superposition eye with almost no clear zone, which minimizes the light shared between ommatidia and reduces the sensitivity of the eye. A progression to superposition optics with a large clear zone, usually associated with night-active or deep-living species, occurs as the animals move deeper in the water column. Regional differences within the eye are also evident, with a largely nonexistent clear zone in the dorsal region and a large clear zone in the ventral region in the eyes of instar 5 animals, the first instar to move to deeper depths. The deepest living instars (10–12) possess superposition optics with a large clear zone throughout the eye, and are significantly more sensitive to light than the younger, shallower instars.
KeywordsLife History Stage Visual Pigment Ventral Region Retinular Cell Crystalline Cone
We wish to thank the crews of the R/Vs New Horizon and Wecoma, as well as volunteers on those cruises, for assistance in procuring animals. J. Piraino graciously provided assistance with TEM. This research was supported by a grant from the National Science Foundation to T. Frank (IBN-0343871) and a Link Foundation/HBOI summer internship to M.K. Olds. Three anonymous reviewers offered insightful comments. This is Harbor Branch contribution number 1726. The experiments described here comply with the current laws of the United States of America.
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