Abstract
Purpose: :
Teleots are a successful vertebrate group, constituting more than 50% of vertebrate species. These fishes are the only vertebrate group that presents spinules from the lateral dendrites of retinal Horizontal cells into cone pedicles. Previously, we observed that the amount of spinules in any given species depended on both taxonomic placing and degree of predatory behavior. The species with the most spinules were also the most predatory and vice versa. A way to study the degree of predatory behavior is measuring patterns of microwear on tooth surfaces. These patterns are related to trophic adaptations and produced by the abrasives in food, during feeding. The aim of this work was to compare the number of spinules per cone pedicle and to correlate these data with tooth microwear parameters and carnivore and predatory behavior, in three species of teleosts.
Methods: :
The study was performed on the following teleosts belonging to perciforme order: Dicentrarchus labrax (moronidae family) and Symphodus tinca and Symphodus roissali (labridae family). Light-adapted fishes were sacrificed and their retinas processed for transmission-electron-microscopy studies. From these studies, we measured the number of spinules, per cone pedicle. In addition, one left-lower premaxillary tooth from each fish was used for microwear analysis with scanning electron microscopy. We measured the density, mean length, and breadth of micro-features, of the teeth.
Results: :
Although the three species were zoobenthic fishes, only Dicentrarchus labrax was carnivore and predator (eating fishes), whereas the two labridae fishes were not. The number of spinules per pedicle was two fold greater (≈9 spinules/pedicle) in the moronidae family that in the labridae ones (≈4 spinules/pedicle). In turn, the dental microwear parameters presented an inverse relationship to the number spinules per pedicle. The density (2.00/100 µm2 vs. 0.76/100µm2), mean length (10µm vs. 6µm), and breadth (2µm vs. 1µm µm) of dental micro-features were nearly two folds larger in the labridae families than in the moronidae one.
Conclusions: :
The amount of spinules per pedicle correlates positively with carnivore and predatory behavior and negatively with dental microwear parameters. These data support the hypothesis that spinules and microwear are the expression of trophic adaptations in teleost fishes.
Keywords: photoreceptors • horizontal cells • plasticity