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J. De Juan, N. Martinez–Ruiz, M.J. Gomez–Torres, A. Lombarte; Are Retinal Spinules, the Reason for the Adaptive Success of Teleosts? . Invest. Ophthalmol. Vis. Sci. 2006;47(13):152.
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Teleosts make up more than 50% of actual vertebrate species, adapted to a wide range of environments. Thus, teleosts can be considered as a very successful adaptive vertebrate group. Besides, teleosts are the only vertebrate group that presents spinules into the cone pedicles from the lateral dendrites of retinal Horizontal Cells. The spinule function is not yet known. The aim of this work is to compare the spinule number per cone pedicle in several species of teleosts, and to correlate this data with predatory behavior, habitat conditions, and taxonomic group.
The study was performed on eight species of teleosts (Morone Americana, Dicentrarchus labrax, Micropterus salmoides, Argyrosomus regius, Symphodus tinca, Coris julis, Psetta maxima, and Cyprinus carpio), belonging to three orders (Perciformes, Pleuronectiformes and Cypriniformes) and six families (Moronidae, Centrarchidae, Sciaenidae, Labridae, Scophthalmidae and Cyprinidae). Fishes were light– and dark– adapted, sacrificed, and their retinas processed for transmission electron microscopy studies. The mean number of spinules per cone pedicle, were calculated.
In light adapted retinas, the number of spinules vary in a wide range between ≈3 (Psetta maxima and Coris julis) and ≈10 (Morone Americana, Micropterus salmoides and Dicentrarchus labrax). In dark adaptation, the number of spinules, is close to zero in all species studied, except in Argyrosomus regius, Symphodus tinca and Coris julis, where the number of spinules per pedicle is ≈3. Perciformes are the order with the highest number of species, and the most number of spinules, in light adapted retinas. Among the Perciformes, the species with the most spinules were also the most predatory and vice versa. On the other hand, Cyprinidae have a lower number of spinules(≈4), as correspond to an omnivore, not predator. Although Psetta maxima is a predator fish, it presents a very low number of spinules.
All of the teleosts studied present spinules invaginated in pedicles during light adaptation. In dark adapted retinas, spinules diminish or disappear. The amount of spinules depends on both taxonomic place and predatory behavior. Thus, the species with the most spinules were also the most predatory and vice versa, independently of the habitat. Perciform is the order whose species have the highest number of spinules. We propose that the spinules are one of the specific mechanisms of the teleosts to facilitate escape and predatory responses.
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