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Available from: James Mcinerney, Oct 13, 2015
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    • "Thus, it would appear that true rod-based scotopic vision is not present in the Agnatha and evolved sometime later in the jawed vertebrates (Collin et al. 2003b). Subsequent analyses using a larger cohort of opsin sequences and different phylogenetic algorithms suggested that RHA and RHB genes cluster with the RH1 and RH2 gene classes of the jawed vertebrates, respectively (Pisani et al. 2006; Davies et al. 2009a), with the corollary that dim-light vision may, in fact, have arisen in lampreys (Pisani et al. 2006). Therefore, the question of when the molecules that mediate dim-light vision evolved remains controversial. "
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    ABSTRACT: In craniates, opsin-based photopigments expressed in the eye encode molecular 'light sensors' that constitute the initial protein in photoreception and the activation of the phototransduction cascade. Since the cloning and sequencing of the first vertebrate opsin gene (bovine rod opsin) nearly 30 years ago (Ovchinnikov Yu 1982, FEBS Letters, 148, 179-191; Hargrave et al. 1983, Biophysics of Structure & Mechanism, 9, 235-244; Nathans & Hogness 1983, Cell, 34, 807-814), it is now well established that variation in the subtypes and spectral properties of the visual pigments that mediate colour and dim-light vision is a prevalent mechanism for the molecular adaptation to diverse light environments. In this review, we discuss the origins and spectral tuning of photopigments that first arose in the agnathans to sample light within the ancient aquatic landscape of the Early Cambrian, detailing the molecular changes that subsequently occurred in each of the opsin classes independently within the main branches of extant jawed gnathostomes. Specifically, we discuss the adaptive changes that have occurred in the photoreceptors of craniates as they met the ecological challenges to survive in quite differing photic niches, including brightly lit aquatic surroundings; the deep sea; the transition to and from land; diurnal, crepuscular and nocturnal environments; and light-restricted fossorial settings. The review ends with a discussion of the limitations inherent to the 'nocturnal-bottleneck' hypothesis relevant to the evolution of the mammalian visual system and a proposition that transition through a 'mesopic-bottleneck' may be a more appropriate model.
    Molecular Ecology 05/2012; 21(13):3121-58. DOI:10.1111/j.1365-294X.2012.05617.x · 6.49 Impact Factor
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    • "Recent work by Pisani incorporated various molecular phylogenetic techniques to shed light on the evolution of color vision within the animal kingdom (Pisani et al., 2006). Examination of different recent taxa led him to hypothesize that the evolution of color vision was coupled with the evolution of different types of opsins, since more than one opsin is required to distinguish light of different wavelength and therefore different color. "
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    ABSTRACT: What drives evolution? This was one of the main questions raised at the final ZOONET meeting in Budapest, Hungary, in November 2008. The meeting marked the conclusion of ZOONET, an EU-funded Marie-Curie Research Training Network comprising nine research groups from all over Europe (Max Telford, University College London; Michael Akam, University of Cambridge; Detlev Arendt, EMBL Heidelberg; Maria Ina Arnone, Stazione Zoologica Anton Dohrn Napoli; Michalis Averof, IMBB Heraklion; Graham Budd, Uppsala University; Richard Copley, University of Oxford; Wim Damen, University of Cologne; Ernst Wimmer, University of Göttingen). ZOONET meetings and practical courses held during the past four years provided researchers from diverse backgrounds--bioinformatics, phylogenetics, embryology, palaeontology, and developmental and molecular biology--the opportunity to discuss their work under a common umbrella of evolutionary developmental biology (Evo Devo). The Budapest meeting emphasized in-depth discussions of the key concepts defining Evo Devo, and bringing together ZOONET researchers with external speakers who were invited to present their views on the evolution of animal form. The discussion sessions addressed four main topics: the driving forces of evolution, segmentation, fossils and phylogeny, and the future of Evo Devo.
    Journal of Experimental Zoology Part B Molecular and Developmental Evolution 11/2009; 312(7):679-85. DOI:10.1002/jez.b.21294 · 2.31 Impact Factor
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    • "Therefore, it may be that at the time in evolutionary history when the jawed and jawless vertebrates split into two lineages, the eyes of lampreys possessed a predominantly photopic visual system based on cone-like photoreceptors. However, at least one type of receptor was undergoing some sort of 'transmutation' to a receptor hybrid, which would subsequently become a 'true rod' with the age of cartilaginous fishes (Walls 1942; Collin & Trezise 2006; Pisani et al. 2006; Davies et al. 2009). (b) Spectral sensitivity The wavelength of maximum absorbance (l max ) of the visual pigment in a given photoreceptor can be a useful, but not definitive, criterion for discriminating between the spectral sensitivity of rods and cones, although in many species this value can be identical (Bowmaker 1995, 2008; figure 1). "
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    ABSTRACT: Meeting the challenge of sampling an ancient aquatic landscape by the early vertebrates was crucial to their survival and would establish a retinal bauplan to be used by all subsequent vertebrate descendents. Image-forming eyes were under tremendous selection pressure and the ability to identify suitable prey and detect potential predators was thought to be one of the major drivers of speciation in the Early Cambrian. Based on the fossil record, we know that hagfishes, lampreys, holocephalans, elasmobranchs and lungfishes occupy critical stages in vertebrate evolution, having remained relatively unchanged over hundreds of millions of years. Now using extant representatives of these 'living fossils', we are able to piece together the evolution of vertebrate photoreception. While photoreception in hagfishes appears to be based on light detection and controlling circadian rhythms, rather than image formation, the photoreceptors of lampreys fall into five distinct classes and represent a critical stage in the dichotomy of rods and cones. At least four types of retinal cones sample the visual environment in lampreys mediating photopic (and potentially colour) vision, a sampling strategy retained by lungfishes, some modern teleosts, reptiles and birds. Trichromacy is retained in cartilaginous fishes (at least in batoids and holocephalans), where it is predicted that true scotopic (dim light) vision evolved in the common ancestor of all living gnathostomes. The capacity to discriminate colour and balance the tradeoff between resolution and sensitivity in the early vertebrates was an important driver of eye evolution, where many of the ocular features evolved were retained as vertebrates progressed on to land.
    Philosophical Transactions of The Royal Society B Biological Sciences 11/2009; 364(1531):2925-40. DOI:10.1098/rstb.2009.0099 · 7.06 Impact Factor
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