Ontogenetic changes in the visual ecology of Northeast Pacific marine fishes.

摘要

The aquatic environment varies in chromatic composition and absolute intensity making it a very dynamic milieu for organisms performing essential visual tasks. Fishes are impressive in their visual adaptations to exploit the photic environment in which they reside. These adaptations are typically driven to match the properties of the photic environment in which a species resides and to the visual tasks performed. But what about the case where different life stages occupy different habitats and perform different visual tasks or behaviors? Research has shown that ontogenetic changes in spectral sensitivity occur, allowing some fish to retune their visual system during development. However, the mechanism fish use and the possible adaptive advantages of shifting visual sensitivity are poorly understood. In this dissertation, microspectrophotometry (MSP) was used to examine the visual pigments of the larvae, juveniles, and adult life stages of 82 species of Northeast Pacific marine fishes for the presence of ontogenetic shifts in spectral sensitivity. Eighty-two percent of the species underwent a shift in spectral sensitivity at the end of the larval period. These shifts were mostly the result of ultraviolet- or violet-sensitivity photoreceptors being replaced by blue-sensitive photoreceptors. Directed studies on the lingcod (Ophiodon elongatus) revealed that the shift from violet- to blue-sensitivity occurs rapidly, within 48 hours, and coincides with the onset of transformation to the juvenile form. The shift also appears to be due to changes in opsin expression opposed to chromophore exchange. Examinations of the developmental stage, diet, spectral distribution of the environment, and changes in the visual system revealed saltatory correlations between all but the spectral distribution of the photic environment inhabited and the visual system changes of lingcod. Additionally, tests of the first-feeding success of lingcod larvae relative to light intensity and wavelength revealed that the visual system was more sensitive to violet light than longer wavelengths. This suggests that short-wavelength sensitivity during the larval stage may serve to not only extend the spectral range of the visual system and improve detection of dim-light signals.