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      Red fluorescence increases with depth in reef fishes, supporting a visual function, not UV protection

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          Abstract

          Why do some marine fishes exhibit striking patterns of natural red fluorescence? In this study, we contrast two non-exclusive hypotheses: (i) that UV absorption by fluorescent pigments offers significant photoprotection in shallow water, where UV irradiance is strongest; and (ii) that red fluorescence enhances visual contrast at depths below −10 m, where most light in the ‘red’ 600–700 nm range has been absorbed. Whereas the photoprotection hypothesis predicts fluorescence to be stronger near the surface and weaker in deeper water, the visual contrast hypothesis predicts the opposite. We used fluorometry to measure red fluorescence brightness in vivo in individuals belonging to eight common small reef fish species with conspicuously red fluorescent eyes. Fluorescence was significantly brighter in specimens from the −20 m sites than in those from −5 m sites in six out of eight species. No difference was found in the remaining two. Our results support the visual contrast hypothesis. We discuss the possible roles fluorescence may play in fish visual ecology and highlight the possibility that fluorescent light emission from the eyes in particular may be used to detect cryptic prey.

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          Cichlid Fish Diversity Threatened by Eutrophication That Curbs Sexual Selection

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            Coral reef fish larvae settle close to home.

            Population connectivity through larval dispersal is an essential parameter in models of marine population dynamics and the optimal size and spacing of marine reserves. However, there are remarkably few direct estimates of larval dispersal for marine organisms, and the actual birth sites of successful recruits have never been located. Here, we solve the mystery of the natal origin of clownfish (Amphiprion polymnus) juveniles by mass-marking via tetracycline immersion all larvae produced in a population. In addition, we established parentage by DNA genotyping all potential adults and all new recruits arriving in the population. Although no individuals settled into the same anemone as their parents, many settled remarkably close to home. Even though this species has a 9-12 day larval duration, one-third of settled juveniles had returned to a 2 hectare natal area, with many settling <100 m from their birth site. This represents the smallest scale of dispersal known for any marine fish species with a pelagic larval phase. The degree of local retention indicates that marine reserves can provide recruitment benefits not only beyond but also within their boundaries.
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              Diversity and Evolution of Coral Fluorescent Proteins

              GFP-like fluorescent proteins (FPs) are the key color determinants in reef-building corals (class Anthozoa, order Scleractinia) and are of considerable interest as potential genetically encoded fluorescent labels. Here we report 40 additional members of the GFP family from corals. There are three major paralogous lineages of coral FPs. One of them is retained in all sampled coral families and is responsible for the non-fluorescent purple-blue color, while each of the other two evolved a full complement of typical coral fluorescent colors (cyan, green, and red) and underwent sorting between coral groups. Among the newly cloned proteins are a “chromo-red” color type from Echinopora forskaliana (family Faviidae) and pink chromoprotein from Stylophora pistillata (Pocilloporidae), both evolving independently from the rest of coral chromoproteins. There are several cyan FPs that possess a novel kind of excitation spectrum indicating a neutral chromophore ground state, for which the residue E167 is responsible (numeration according to GFP from A. victoria). The chromoprotein from Acropora millepora is an unusual blue instead of purple, which is due to two mutations: S64C and S183T. We applied a novel probabilistic sampling approach to recreate the common ancestor of all coral FPs as well as the more derived common ancestor of three main fluorescent colors of the Faviina suborder. Both proteins were green such as found elsewhere outside class Anthozoa. Interestingly, a substantial fraction of the all-coral ancestral protein had a chromohore apparently locked in a non-fluorescent neutral state, which may reflect the transitional stage that enabled rapid color diversification early in the history of coral FPs. Our results highlight the extent of convergent or parallel evolution of the color diversity in corals, provide the foundation for experimental studies of evolutionary processes that led to color diversification, and enable a comparative analysis of structural determinants of different colors.
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                Author and article information

                Journal
                Proc Biol Sci
                Proc. Biol. Sci
                RSPB
                royprsb
                Proceedings of the Royal Society B: Biological Sciences
                The Royal Society
                0962-8452
                1471-2954
                7 September 2014
                7 September 2014
                : 281
                : 1790
                : 20141211
                Affiliations
                [1 ]Animal Evolutionary Ecology, Institution for Evolution and Ecology, Department of Biology, Faculty of Science, University of Tübingen , Auf der Morgenstelle 28, 72076 Tübingen, Germany
                [2 ]Department of Marine Science, Faculty of Science, Suez Canal University , Ismailia, Egypt
                Author notes
                [†]

                These authors contributed equally to this study.

                Article
                rspb20141211
                10.1098/rspb.2014.1211
                4123709
                25030989
                89165885-956c-4fda-a443-10202d9fed5d

                © 2014 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/, which permits unrestricted use, provided the original author and source are credited.

                History
                : 19 May 2014
                : 25 June 2014
                Categories
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                Custom metadata
                September 7, 2014

                Life sciences
                fluorescence,photoprotection,colour contrast,visual ecology,marine fish
                Life sciences
                fluorescence, photoprotection, colour contrast, visual ecology, marine fish

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