The energetic cost of vision and the evolution of eyeless Mexican cavefish – ScienceOpen
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      The energetic cost of vision and the evolution of eyeless Mexican cavefish

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          Abstract

          The loss of vision during the evolution of cave Mexican tetra considerably reduced the energetic burden of neural tissue.

          Abstract

          One hypothesis for the reduction of vision in cave animals, such as the eyeless Mexican cavefish, is the high energetic cost of neural tissue and low food availability in subterranean habitats. However, data on relative brain and eye mass in this species or on any measure of the energetic cost of neural tissue are not available, making it difficult to evaluate the “expensive tissue hypothesis.” We show that the eyes and optic tectum represent significant metabolic costs in the eyed phenotype. The cost of vision was calculated to be 15% of resting metabolism for a 1-g fish, decreasing to 5% in an 8.5-g fish as relative eye and brain size declined during growth. Our results demonstrate that the loss of the visual system in the cave phenotype substantially lowered the amount of energy expended on expensive neural tissue during diversification into subterranean rivers, in particular for juvenile fish.

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          Most cited references22

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          Ratio of central nervous system to body metabolism in vertebrates: its constancy and functional basis.

          We present and document an hypothesis that healthy adults of most vertebrate species use 2-8% of their basal metabolism for the central nervous system (CNS). This relationship is constant across all classes of vertebrates, as we found by examining data from 42 species, including 3 fish, 3 amphibia, 2 reptiles, 6 birds, and 28 mammals. To explain its constancy, we hypothesize that an optimal functional relationship between the energy requirements of an animal's executor system (muscle metabolism) and its control system (CNS metabolism) was established early in vertebrate evolution. Three types of exceptional cases are discussed in terms of the hypothesis: very large animals, domesticated animals, and primates.
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            Cryptic variation in morphological evolution: HSP90 as a capacitor for loss of eyes in cavefish.

            In the process of morphological evolution, the extent to which cryptic, preexisting variation provides a substrate for natural selection has been controversial. We provide evidence that heat shock protein 90 (HSP90) phenotypically masks standing eye-size variation in surface populations of the cavefish Astyanax mexicanus. This variation is exposed by HSP90 inhibition and can be selected for, ultimately yielding a reduced-eye phenotype even in the presence of full HSP90 activity. Raising surface fish under conditions found in caves taxes the HSP90 system, unmasking the same phenotypic variation as does direct inhibition of HSP90. These results suggest that cryptic variation played a role in the evolution of eye loss in cavefish and provide the first evidence for HSP90 as a capacitor for morphological evolution in a natural setting.
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              Evolutionary convergence on sleep loss in cavefish populations.

              Patterns of sleep vary widely among species, but the functional and evolutionary principles responsible for this diversity remain unknown. The characin fish, Astyanax mexicanus, has eyed surface and numerous blind cave populations. The cave populations are largely independent in their origins, and the species is ideal for studying the genetic bases of convergent evolution. Here we show that this system is also uniquely valuable for the investigation of variability in patterns of sleep. We find that a clearly defined change in ecological conditions, from surface to cave, is correlated with a dramatic reduction in sleep in three independently derived cave populations of A. mexicanus. Analyses of surface × cave hybrids show that the alleles for reduced sleep in the Pachón and Tinaja cave populations are dominant in effect to the surface alleles. Genetic analysis of hybrids between surface and Pachón cavefish suggests that only a small number of loci with dominant effects are involved. Our results demonstrate that sleep is an evolutionarily labile phenotype, highly responsive to changes in ecological conditions. To our knowledge, this is the first example of a single species with a convergence on sleep loss exhibited by several independently evolved populations correlated with population-specific ecologies. Copyright © 2011 Elsevier Ltd. All rights reserved.
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                Author and article information

                Journal
                Sci Adv
                Sci Adv
                SciAdv
                advances
                Science Advances
                American Association for the Advancement of Science
                2375-2548
                September 2015
                11 September 2015
                : 1
                : 8
                : e1500363
                Affiliations
                Department of Biology, Lund University, Lund 22362, Sweden.
                Author notes
                [*]

                Present address: Plant and Food Research, Seafood Technologies Group, Nelson 7040, New Zealand.

                []Corresponding author. E-mail: damian.moran@ 123456plantandfood.co.nz
                Article
                1500363
                10.1126/sciadv.1500363
                4643782
                26601263
                c21eb885-d285-42ad-8403-de490420b0d3
                Copyright © 2015, The Authors

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited.

                History
                : 27 March 2015
                : 28 June 2015
                Funding
                Funded by: Research Executive Agency (BE);
                Award ID: ID0E4MAG2359
                Award ID: PIEF-GA-2009-251874
                Award Recipient :
                Categories
                Research Article
                Research Articles
                SciAdv r-articles
                Eye Evolution
                Custom metadata
                Meann Ramirez

                biology,brain evolution,eye evolution,physiological energetics,cave,subterranean

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