Adaptation in the optical properties of the crystalline lens in the eyes of the Lessepsian migrantSiganus rivulatus

Abstract

SUMMARYVision is an important source of information for many animals. The crystalline lens plays a central role in the visual pathway and hence the ecology of fishes. In this study, we tested whether the different light regimes in the Mediterranean and Red Seas have an effect on the optical properties of the lenses in the rivulated rabbitfish, Siganus rivulatus. This species has migrated through the Suez Canal from the Red Sea and established a vital population in the Mediterranean Sea. Longitudinal spherical aberration curves and focal lengths of the fish lenses were measured by laser scans and compared between the two populations. In addition, rivulated rabbitfish from the Mediterranean Sea were exposed to colored light (yellow, green and blue) and unfiltered light for periods of 1 or 13days to test for short-term adjustments. Lens focal length was significantly longer (3%) in the Rea Sea population. The shorter focal length of the Mediterranean population can be explained as an adaptation to the dimmer light environment, as this difference makes the Mediterranean eyes 5% more sensitive than the eyes of the Red Sea population. The difference may be due to genetic differences or, more likely, adaptive developmental plasticity. Short-term regulatory mechanisms do not seem to be involved.

An Overview of the Penguin Visual System

“…One such aspect is the gradation of the refractive index, as described by Matthiessen [ 77 ], in both marine and terrestrial vertebrates, but which has not been measured in any penguin. Multifocality in the crystalline lens of fish is thought to adjust for chromatic aberration and can vary depending on the waters the fish inhabits [ 105 ]. The fish lens is spherical, with a focal length always around 2.55 lens radii—i.e., f/r = 2.55, range 2.40 to 2.82 [ 77 ].…”