| The teleost retina changes throughout life by continuously adding new photoreceptor cells and other retinal neurons in the constantly growing eye. Most teleost fish species begin life with cone-dominated retinas, and add rods as they mature. The work presented here, however, shows that fishes of the basal teleost subdivision Elopomorpha (united primarily on the basis of a shared larval form called a leptocephalus) exhibit a very different pattern of retinal development, beginning life rod-dominated, and adding cones as they mature. Persistent neurogenesis allows the elopomorph retina to change over the course of development in distributions and functional morphology of photoreceptor cells in the retina. The similar (and unusual) pattern of retinal development in the elopomorphs studied here provides new evidence that the Elopomorpha are indeed a monophyletic assemblage. From similar larval morphology retinal architecture, however, there occurs great divergence among elopomorph species at metamorphosis in body form, ecology, and functional morphology of the retina. Employing anti-opsin immunocytochemistry, transmission electron microscopy, light microscopy and microspectrophotometry, the work presented here shows that retinas of four ecologically distinct elopomorph fishes (Order Elopiformes: Megalops atlanticus, Elops saurus; Order Albuiliformes: Albula vulpes; Order Anguilliformes: Myrophis punctatus) diverge dramatically in number and distribution of different functional classes of photoreceptors in concordance with ontogenic shifts in habitat and behavior. Experimental rearing of metamorphosing and adult elopomorphs in controlled lighting conditions showed that some aspects of developmental changes in retinal architecture are likely genetically based, but that there is some degree of developmental plasticity in the retina influenced by light environment. Developmental changes in retinal form and function allow elopomorph fishes to maintain adequate visual function as they undergo ontogenic shifts in habitat and behavior. Because retinal development is at least partially genetically predetermined, anthropogenic influences on coastal optical water quality might have profound effects on the survival of young fishes recruiting to volatile coastal environments. |
