The Cyclostome Retina

Holmberg, Kaj

doi:10.1007/978-3-642-66468-7_2

Cited by 25 publications

(28 citation statements)

References 31 publications

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“…Consistent with this scenario is the situation in the most primitive chordates, the hagfish, in which ciliary PRCs connect directly to ganglion cells, and bipolar cells appear to be absent (Holmberg 1977). The neural connectivity of pineal photoreceptors in non-mammalian vertebrates also suggests that bipolar cells are late additions specific to vertebrate lateral eyes (Lamb et al 2007;Nilsson & Arendt 2008).…”

Section: The Evolution Of Visual Eyes and Bipolar Interneuronsmentioning

confidence: 66%

The ‘division of labour’ model of eye evolution

Arendt

Hausen

Purschke

2009

Phil. Trans. R. Soc. B

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The 'division of labour' model of eye evolution is elaborated here. We propose that the evolution of complex, multicellular animal eyes started from a single, multi-functional cell type that existed in metazoan ancestors. This ancient cell type had at least three functions: light detection via a photoreceptive organelle, light shading by means of pigment granules and steering through locomotor cilia. Located around the circumference of swimming ciliated zooplankton larvae, these ancient cells were able to mediate phototaxis in the absence of a nervous system. This precursor then diversified, by cell-type functional segregation, into sister cell types that specialized in different subfunctions, evolving into separate photoreceptor cells, shading pigment cells (SPCs) or ciliated locomotor cells. Photoreceptor sensory cells and ciliated locomotor cells remained interconnected by newly evolving axons, giving rise to an early axonal circuit. In some evolutionary lines, residual functions prevailed in the specialized cell types that mirror the ancient multi-functionality, for instance, SPCs expressing an opsin as well as possessing rhabdomer-like microvilli, vestigial cilia and an axon. Functional segregation of cell types in eye evolution also explains the emergence of more elaborate photosensory-motor axonal circuits, with interneurons relaying the visual information.

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Section: The Evolution Of Visual Eyes and Bipolar Interneuronsmentioning

confidence: 66%

The ‘division of labour’ model of eye evolution

Arendt

Hausen

Purschke

2009

Phil. Trans. R. Soc. B

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“…Although the eyes of hagfishes are rudimentary, they may hold important clues about the early evolution of the vertebrate eye (Lamb et al, 2007). However, since they lack a lens and further research is required to assess the differentiation of the retinal photoreceptor types (Holmberg, 1977), an analysis of the eyes of adult lampreys, which possess well-developed eyes that closely follow the eye design of jawed vertebrates (Walls, 1942;Duke-Elder, 1958), may hold more promise in tracing the origin of multifocal optical systems.…”

Section: Introductionmentioning

confidence: 99%

Early evolution of multifocal optics for well-focused colour vision in vertebrates

Gustafsson

Collin

Kröger

2008

Journal of Experimental Biology

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“…c The retina of the hagfish, Eptatretus stouti, viewed using light microscopy; OS outer segments; RC receptor cells; OFL outer fiber layer (=outer plexiform layer); IC inner cells (=retinal ganglion cells); IFL inner fiber layer; V vitreous. The images are reproduced with permission as follows: a Dr Paddy Ryan ©Ryan Photographic; b ©Australian Museum, photo Mark McGrouther; c from Holmberg (1977), reproduced by permission of Springer survived for hundreds of millions of years, in comparison with the degeneration that has occurred in just thousands of years in cavefish, it seems clear that the organ must have been of considerable value to the survival of the hagfish. On the degeneration hypothesis, one would need to explain how it was advantageous to hagfish for the following to have occurred: (a) for a three-layered retina to have reverted to a two-layered structure; (b) for the processing power of the bipolar cells to have been dispensed with; (c) for a reversion to a more rudimentary photoreceptor structure; (d) for the disappearance of the lens, cornea, iris, and ocular muscles, all without trace; (e) for the covering of the eye by skin; and (f) for the projection of the retinal ganglion cells to be redirected from the tectum primarily to the hypothalamus.…”

Section: The Hagfish Eyementioning

confidence: 99%

The Origin of the Vertebrate Eye

2008

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In his considerations of "organs of extreme perfection," Charles Darwin described the evidence that would be necessary to support the evolutionary origin of the eye, namely, demonstration of the existence of "numerous gradations" from the most primitive eye to the most perfect one, where each such tiny change had provided a survival advantage (however slight) to the organism possessing the subtly altered form. In this paper, we discuss evidence indicating that the vertebrate eye did indeed evolve through numerous subtle changes. The great majority of the gradual transitions that did occur have not been preserved to the present time, either in the fossil record or in extant species; yet clear evidence of their occurrence remains. We discuss the remarkable "eye" of the hagfish, which has features intermediate between a simple light detector and an image-forming camera-like eye and which may represent a step in the evolution of our eye that can now be studied by modern methods. We also describe the important clues to the evolutionary origin of the vertebrate eye that can be found by studying the embryological development of our own eye, by examining the molecular genetic record preserved in our own genes and in the genes of other vertebrates, and through consideration of the imperfections (or evolutionary "scars") in the construction of our eye. Taking these findings together, it is possible to discuss in some detail how the vertebrate eye evolved.

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The Cyclostome Retina

Cited by 25 publications

References 31 publications

The ‘division of labour’ model of eye evolution

The ‘division of labour’ model of eye evolution

Early evolution of multifocal optics for well-focused colour vision in vertebrates

The Origin of the Vertebrate Eye

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