Abstract
Purpose: :
Most teleosts have excellent vision and eyes perfectly adapted to their aquatic environment. The multifocal lens, correcting for spherical and chromatic aberrations, is an ancient adaptation found in all vertebrate groups. Even lampreys, the most basic vertebrates with well developed eyes, have this lens type. On the other hand, aspects of the eye such as the lens suspension as well as the structure and shape of the lens fiber cells differ considerably between groups. In a recent study, up to six additional suspensory ligaments supporting the lens were found and confirmed in several teleost families. The purpose of this study was to compare lens suspension and lens fiber cell structure in teleosts with those in lampreys and one of the tetrapods’ closest fish relative, the lungfish.
Methods: :
Light and electron microscopy were used to study the lens suspension and lens fiber cell structure in one species of lamprey, the river lamprey (Lampetra fluviatilis), and one species of lungfish, the marbled lungfish (Protopterus aethiopicus aethiopicus).
Results: :
Previously undescribed suspensory structures for the lens were found in both the lamprey and the lungfish eyes. In both species, the spherical lens is held in place by a thin equatorial membrane. The lens fiber cells of the lampreys were found to be irregular in shape whereas lungfish lens fiber cells are more regular, than those in other vertebrates. Furthermore, both lamprey and lungfish fiber cells are covered with small protrusions that are largely absent from teleost lens fiber cells.
Conclusions: :
The lens suspension in lampreys and lungfish resemble each other closely and differ markedly from the suspensory systems in teleosts. The abundant protrusions on the lens fiber cells are another similarity between lampreys and lungfishes. These eye and lens characteristics will be studied in bony fish that are generally considered to be evolutionary basal to teleosts (e.g Polypterus, Lepisosteus, Acipenser ) for additional comparisons. Hopefully this will contribute to a better insight into the vividly debated early evolutionary branching of vertebrates.
Keywords: development • microscopy: electron microscopy • accomodation