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Reference #: MEN-1019-849108
Submit Date: 04/26/2002 14:13:04-0500
Presentation Type: platform
CONTACT: Michael Menaker
Department of Biology/Gilmer Hall P.O.B. 400328 University of Virginia Charlottesville,
VA 22904-4328
Non-visual responses of vertebrates to
visible light: the evolution of a neglected sensory modality
AUTHOR GROUP:
Michael Menaker 1
Department of Biology/Gilmer Hall P.O.B. 400328 University of Virginia Charlottesville, VA 22904-4328 1
ABSTRACT:
Experiments demonstrating that some vertebrates perceive visible light with extra-retinal photoreceptors were conducted almost 100 years ago by von Frisch and Scharrer. They trained enucleated fish to associate light with food. In the 1930s Benoit induced testis growth in enucleated ducks by exposing them to long days. Beginning in the 1960s my students and I showed that the locomotor activity rhythms of enucleated sparrows could be synchronized to dim light-dark cycles and that their reproductive responses to daylength were unchanged by enucleation. We then extended these results to reptiles and others extended them to fish and amphibians. By now extra-retinal photoreception has been documented in every non-mammalian vertebrates species in which it has been sought (and in many invertebrates as well). The details of sensitivity and interaction with retinal photoreceptors suggest that the underlying photoreceptive system is highly specialized and adapted for its role in reporting irradiance; it is likely to have preceded vision in the evolution of multicellular organisms and may have been retained because imaging forming machinery is unsuitable for irradiance detection. Mammals are different and use their eyes for both image formation and irradiance detection. Why are mammals different from all other vertebrates? It may be because in the course of their evolution they passed through a "nocturnal bottleneck" which selected for sensitive irradiance detectors in a single location. But irradiance detection and vision are performed by completely different populations of retinal photoreceptors, each of which has response properties suited to its role. Mammalian retinal irradiance detectors have been recently identified and characterized and will be the subject of intense discussion in the symposium on "Circadian Photoreception and Transduction" (D1, Sunday AM).
Keywords: circadian rhythm, entrainment, photoreceptors, retina
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