Evolution of the vertebrate eye: opsins, photoreceptors, retina and eye cup

Evolution of the vertebrate eye: opsins, photoreceptors, retina and eye cup
 

Authors: Trevor D. Lamb, Shaun P. Collin and Edward N. Pugh, Jr

Abstract

Charles Darwin appreciated the conceptual difficulty in accepting that an organ as wonderful as the vertebrate eye could have evolved through natural selection. He reasoned that if appropriate gradations could be found that were useful to the animal and were inherited, then the apparent difficulty would be overcome. Here, we review a wide range of findings that capture glimpses of the gradations that appear to have occurred during eye evolution, and provide a scenario for the unseen steps that have led to the emergence of the vertebrate eye.

 

Central Role for the Lens in Cave Fish Eye Degeneration

Central Role for the Lens in Cave Fish Eye Degeneration

Authors: Yoshiyuki Yamamoto & William R. Jeffery

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Abstract

Astyanax mexicanus is a teleost with eyed surface-dwelling and eyeless cavedwelling forms. Eye formation is initiated in cave Þsh embryos, but the eye subsequently arrests and degenerates. The surface Þsh lens stimulates growth and development after transplantation into the cave Þsh optic cup, restoring optic tissues lost during cave Þsh evolution. Conversely, eye growth and development are retarded following transplantation of a surface Þsh lens into a cave Þsh optic cup or lens extirpation. These results show that evolutionary changes in an inductive signal from the lens are involved in cave Þsh eye degeneration.

Comparative Morphology of the Eye (With Particular Attention to the Retina) in Various Species of Cardinal Fish (Apogonidae, Teleostei).

Comparative Morphology of the Eye (With Particular Attention to the Retina) in Various Species of Cardinal Fish (Apogonidae, Teleostei).

Authors: Lev Fishelson, Guy Ayalon, Adi Zverdling & Roi Holzman.

 

ABSTRACT

Various parameters of the eye dimension and structure have been compared in 15 species of cardinal fish (Apogonidae), including both nocturnal and diurnal forms, mostly inhabiting rocky habitats in tropical and subtropical regions. In general, in the nocturnal forms the eye and retina are larger than in the diurnal fish of similar dimensions. In the nocturnal species, eye diameter to body length is ca. 12–13%, whereas in the diurnal species it is less than 10%. Retina size in adult fish of the various species varies from 20 mm2 to 183 mm2. Cytological examination of the studied retinas revealed that they are composes, additional to rods (20–40 micrômetros), of both bulbous and slender double cones, as well as single cones. These cones form a mosaic comprising four double with one single in the center, a pattern that is less prominent at the periphery of the retina and more so in the fundus. The rod ellipsoids reveal normal mitochondria, whereas the cones bear ellipsoids featuring opaque and unusual, ellipsosomelike mitochondria. The number of rods in a retinas varies from 15 to 128 million, and the number of cones from 460,000 to 5,673,000. As revealed in cardinal fish of similar dimensions, the number of visual cells found in the retina is much higher in the nocturnal than in the diurnal species. The ecological and developmental aspects of the observed phenomena are discussed.

Key words: cardinal fish; eye dimension comparison; retina size; visual cells; ellipsoids and ellipsosomes; synapses.

 

The Evolution of eyes / A Evolução do Olho.

The Evolution of eyes

A Evolução do Olho.

Authors: Michael F. Land & Russell D Fernald

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Since the earth formed more than 5 billion years ago, sunlight has been the most potent selective force to control the evolution of living organisms. Consequences of this solar selection are most evident in eyes, the premier sensory outposts of the brain. Because organisms use light to see, eyes have evo lved into many shapes, sizes, and designs; within these structures, highlyconserved protein molecules for catching photons and bending light rays have also evolved. Although eyes themselves demonstrate many different solutions to the problem of obtaining an image-solutions reached relatively late in evolution-some of the molecules important for sight are, in fact, the same as in the earliest times. This suggests that once suitable biochemical solutions are found, they are retained, even though their "packaging" varies greatly. In this review, we concentrate on the diversity of eye types and their optical evolution, but first we consider briefly  evolution at the more fundamental levels of molecules and cells.

Evaluation of Female Mate Choice Cues in a Group of Lake Malawi Mbuna (Cichlidae)

Evaluation of Female Mate Choice Cues in a Group of Lake Malawi Mbuna (Cichlidae)

Authors: REBECCA JORDAN, KAREN KELLOGG, FRANCIS JUANES, AND JAY STAUFFER JR.
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The mechanisms that underlie the diversity of cichlids in the East African Great Lakes are poorly understood. Sexual selection through female choice based on male body coloration has often been suggested as a driving force behind the speciation of these fishes. The objectives of this study were to investigate, through mate choice trials, the cues that guide species-isolating female choice. In a group of sympatric Lake Malawi mbuna (rock-dwelling fish), we investigated both visual and chemical cues that might guide female choice by giving gravid females a choice between a heterospecific and a conspecific male. Visual cues, in contrast to olfactory cues, were sufficient to stimulate courtship and thus guide female choice of males. Furthermore, in contrast to other studies on related species, we found that females courted only with conspecifics even if color was not a cue. Species-isolating female choice is likely based primarily on visual information.

Comparative visual function in elasmobranchs: Spatial arrangement and ecological correlates of photoreceptor and ganglion cell distributions. / Função visual comparativa em elasmobrânquios: arranjo espacial e correlações ecológicas de distribuições fotorreceptoras e células ganglionares.

Comparative visual function in elasmobranchs: Spatial arrangement and ecological correlates of photoreceptor and ganglion cell distributions.

Autores: Lenore Litherland e Shaun C. Collin

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Abstract
The topographic analysis of retinal ganglion and photoreceptor cell distributions yields valuable information for assessing the visual capabilities and behavioral ecology of vertebrates. This study examines whole-mounted retinas of four elasmobranch species, the ornate wobbegong, Orectolobus ornatus; the whitetip reef shark, Triaenodon obesus; the epaulette shark, Hemiscyllium ocellatum; and the east Australia shovelnose ray, Aptychotrema rostrata, for regional specializations mediating zones of improved visual ability. These species represent a range of lifestyles: benthic, mid-water, diurnal, and nocturnal. Both photoreceptors (visualized using differential interference contrast optics) and ganglion cells (stained with cresyl violet) in the retina are extensively sampled, and their spatial distribution is found to be nonuniform, exhibiting areae or ‘‘visual streaks.’’ In general, the topographic distributions of both cell populations are in register and match well with respect to the location of regions of high density. However, the location of peaks in rod and cone densities can vary within a retina, indicating that preferential sampling of different regions of the visual field may occur in photopic and scotopic vision. Anatomical measures of the optical limits of resolving power, indicated by intercone spacing, range from 3.8 to 13.1 cycles/deg. Spatial limits of resolving power, calculated from ganglion cell spacing, range from 2.6 to 4.3 cycles/deg. Summation ratios, assessed by direct comparison of cell densities of photoreceptors (input cells) and ganglion cells (output cells), at more than 150 different loci across the retina, show topographic differences in signal convergence (ranging from 25:1 to over 70:1). Species-specific retinal specializations strongly correlate to the habitat and feeding behavior of each species.

Keywords: Visual ecology, Retinal topography, Photoreceptors, Ganglion cells, Elasmobranchs.