1
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Lin JJ, Wang FY, Chung WY, Wang TY. The genomic evolution of visual opsin genes in amphibians. Vision Res 2024; 222:108447. [PMID: 38906036 DOI: 10.1016/j.visres.2024.108447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Revised: 05/15/2024] [Accepted: 05/16/2024] [Indexed: 06/23/2024]
Abstract
Among tetrapod (terrestrial) vertebrates, amphibians remain more closely tied to an amphibious lifestyle than amniotes, and their visual opsin genes may be adapted to this lifestyle. Previous studies have discussed physiological, morphological, and molecular changes in the evolution of amphibian vision. We predicted the locations of the visual opsin genes, their neighboring genes, and the tuning sites of the visual opsins, in 39 amphibian genomes. We found that all of the examined genomes lacked the Rh2 gene. The caecilian genomes have further lost the SWS1 and SWS2 genes; only the Rh1 and LWS genes were retained. The loss of the SWS1 and SWS2 genes in caecilians may be correlated with their cryptic lifestyles. The opsin gene syntenies were predicted to be highly similar to those of other bony vertebrates. Moreover, dual syntenies were identified in allotetraploid Xenopus laevis and X. borealis. Tuning site analysis showed that only some Caudata species might have UV vision. In addition, the S164A that occurred several times in LWS evolution might either functionally compensate for the Rh2 gene loss or fine-tuning visual adaptation. Our study provides the first genomic evidence for a caecilian LWS gene and a genomic viewpoint of visual opsin genes by reviewing the gains and losses of visual opsin genes, the rearrangement of syntenies, and the alteration of spectral tuning in the course of amphibians' evolution.
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Affiliation(s)
- Jinn-Jy Lin
- National Center for High-performance Computing, National Applied Research Laboratories, Hsinchu, Taiwan
| | - Feng-Yu Wang
- Taiwan Ocean Research Institute, National Applied Research Laboratories, Kaohsiung, Taiwan
| | - Wen-Yu Chung
- Department of Computer Science and Information Engineering, National Kaohsiung University of Science and Technology, Kaohsiung, Taiwan
| | - Tzi-Yuan Wang
- Biodiversity Research Center, Academia Sinica, Taipei, Taiwan.
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2
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Schott RK, Fujita MK, Streicher JW, Gower DJ, Thomas KN, Loew ER, Bamba Kaya AG, Bittencourt-Silva GB, Guillherme Becker C, Cisneros-Heredia D, Clulow S, Davila M, Firneno TJ, Haddad CFB, Janssenswillen S, Labisko J, Maddock ST, Mahony M, Martins RA, Michaels CJ, Mitchell NJ, Portik DM, Prates I, Roelants K, Roelke C, Tobi E, Woolfolk M, Bell RC. Diversity and Evolution of Frog Visual Opsins: Spectral Tuning and Adaptation to Distinct Light Environments. Mol Biol Evol 2024; 41:msae049. [PMID: 38573520 PMCID: PMC10994157 DOI: 10.1093/molbev/msae049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2023] [Revised: 02/07/2024] [Accepted: 02/26/2024] [Indexed: 04/05/2024] Open
Abstract
Visual systems adapt to different light environments through several avenues including optical changes to the eye and neurological changes in how light signals are processed and interpreted. Spectral sensitivity can evolve via changes to visual pigments housed in the retinal photoreceptors through gene duplication and loss, differential and coexpression, and sequence evolution. Frogs provide an excellent, yet understudied, system for visual evolution research due to their diversity of ecologies (including biphasic aquatic-terrestrial life cycles) that we hypothesize imposed different selective pressures leading to adaptive evolution of the visual system, notably the opsins that encode the protein component of the visual pigments responsible for the first step in visual perception. Here, we analyze the diversity and evolution of visual opsin genes from 93 new eye transcriptomes plus published data for a combined dataset spanning 122 frog species and 34 families. We find that most species express the four visual opsins previously identified in frogs but show evidence for gene loss in two lineages. Further, we present evidence of positive selection in three opsins and shifts in selective pressures associated with differences in habitat and life history, but not activity pattern. We identify substantial novel variation in the visual opsins and, using microspectrophotometry, find highly variable spectral sensitivities, expanding known ranges for all frog visual pigments. Mutations at spectral-tuning sites only partially account for this variation, suggesting that frogs have used tuning pathways that are unique among vertebrates. These results support the hypothesis of adaptive evolution in photoreceptor physiology across the frog tree of life in response to varying environmental and ecological factors and further our growing understanding of vertebrate visual evolution.
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Affiliation(s)
- Ryan K Schott
- Department of Biology and Centre for Vision Research, York University, Toronto, Ontario, Canada
- Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
| | - Matthew K Fujita
- Department of Biology, Amphibian and Reptile Diversity Research Center, The University of Texas at Arlington, Arlington, TX, USA
| | | | | | - Kate N Thomas
- Department of Biology, Amphibian and Reptile Diversity Research Center, The University of Texas at Arlington, Arlington, TX, USA
- Natural History Museum, London, UK
| | - Ellis R Loew
- Department of Biomedical Sciences, Cornell University College of Veterinary Medicine, Ithaca, NY, USA
| | | | | | - C Guillherme Becker
- Department of Biology and One Health Microbiome Center, Center for Infectious Disease Dynamics, The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, USA
| | - Diego Cisneros-Heredia
- Laboratorio de Zoología Terrestre, Instituto de Biodiversidad Tropical IBIOTROP, Colegio de Ciencias Biológicas y Ambientales, Universidad San Francisco de Quito USFQ, Quito, Ecuador
| | - Simon Clulow
- Centre for Conservation Ecology and Genomics, Institute for Applied Ecology, University of Canberra, Bruce, ACT, Australia
| | - Mateo Davila
- Laboratorio de Zoología Terrestre, Instituto de Biodiversidad Tropical IBIOTROP, Colegio de Ciencias Biológicas y Ambientales, Universidad San Francisco de Quito USFQ, Quito, Ecuador
| | - Thomas J Firneno
- Department of Biological Sciences, University of Denver, Denver, USA
| | - Célio F B Haddad
- Department of Biodiversity and Center of Aquaculture—CAUNESP, I.B., São Paulo State University, Rio Claro, São Paulo, Brazil
| | - Sunita Janssenswillen
- Amphibian Evolution Lab, Biology Department, Vrije Universiteit Brussel, Brussels, Belgium
| | - Jim Labisko
- Natural History Museum, London, UK
- Centre for Biodiversity and Environment Research, Department of Genetics, Evolution and Environment, University College London, London, UK
- Island Biodiversity and Conservation Centre, University of Seychelles, Mahé, Seychelles
| | - Simon T Maddock
- Natural History Museum, London, UK
- Island Biodiversity and Conservation Centre, University of Seychelles, Mahé, Seychelles
- School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne, UK
| | - Michael Mahony
- Department of Biological Sciences, The University of Newcastle, Newcastle 2308, Australia
| | - Renato A Martins
- Programa de Pós-graduação em Conservação da Fauna, Universidade Federal de São Carlos, São Carlos, Brazil
| | | | - Nicola J Mitchell
- School of Biological Sciences, The University of Western Australia, Crawley, WA 6009, Australia
| | - Daniel M Portik
- Department of Herpetology, California Academy of Sciences, San Francisco, CA, USA
| | - Ivan Prates
- Department of Biology, Lund University, Lund, Sweden
| | - Kim Roelants
- Amphibian Evolution Lab, Biology Department, Vrije Universiteit Brussel, Brussels, Belgium
| | - Corey Roelke
- Department of Biology, Amphibian and Reptile Diversity Research Center, The University of Texas at Arlington, Arlington, TX, USA
| | - Elie Tobi
- Gabon Biodiversity Program, Center for Conservation and Sustainability, Smithsonian National Zoo and Conservation Biology Institute, Gamba, Gabon
| | - Maya Woolfolk
- Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
- Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, MA, USA
| | - Rayna C Bell
- Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
- Department of Herpetology, California Academy of Sciences, San Francisco, CA, USA
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3
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Van Nynatten A, Duncan AT, Lauzon R, Sheldon TA, Chen SK, Lovejoy NR, Mandrak NE, Chang BSW. Adaptive Evolution of Nearctic Deepwater Fish Vision: Implications for Assessing Functional Variation for Conservation. Mol Biol Evol 2024; 41:msae024. [PMID: 38314890 PMCID: PMC10896662 DOI: 10.1093/molbev/msae024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Revised: 12/15/2023] [Accepted: 01/05/2024] [Indexed: 02/07/2024] Open
Abstract
Intraspecific functional variation is critical for adaptation to rapidly changing environments. For visual opsins, functional variation can be characterized in vitro and often reflects a species' ecological niche but is rarely considered in the context of intraspecific variation or the impact of recent environmental changes on species of cultural or commercial significance. Investigation of adaptation in postglacial lakes can provide key insight into how rapid environmental changes impact functional evolution. Here, we report evidence for molecular adaptation in vision in 2 lineages of Nearctic fishes that are deep lake specialists: ciscoes and deepwater sculpin. We found depth-related variation in the dim-light visual pigment rhodopsin that evolved convergently in these 2 lineages. In vitro characterization of spectral sensitivity of the convergent deepwater rhodopsin alleles revealed blue-shifts compared with other more widely distributed alleles. These blue-shifted rhodopsin alleles were only observed in deep clear postglacial lakes with underwater visual environments enriched in blue light. This provides evidence of remarkably rapid and convergent visual adaptation and intraspecific functional variation in rhodopsin. Intraspecific functional variation has important implications for conservation, and these fishes are of conservation concern and great cultural, commercial, and nutritional importance to Indigenous communities. We collaborated with the Saugeen Ojibway Nation to develop and test a metabarcoding approach that we show is efficient and accurate in recovering the ecological distribution of functionally relevant variation in rhodopsin. Our approach bridges experimental analyses of protein function and genetics-based tools used in large-scale surveys to better understand the ecological extent of adaptive functional variation.
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Affiliation(s)
- Alexander Van Nynatten
- Department of Biological Science, University of Toronto Scarborough, Scarborough, Ontario, Canada
| | - Alexander T Duncan
- Faculty of Natural Resources Management, Lakehead University, Thunder Bay, Ontario, Canada
- Fisheries Assessment Program, Chippewas of Nawash Unceded First Nation, Neyaashiinigmiing, Ontario, Canada
| | - Ryan Lauzon
- Fisheries Assessment Program, Chippewas of Nawash Unceded First Nation, Neyaashiinigmiing, Ontario, Canada
| | | | - Steven K Chen
- Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada
| | - Nathan R Lovejoy
- Department of Biological Science, University of Toronto Scarborough, Scarborough, Ontario, Canada
- Department of Ecological and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Nicholas E Mandrak
- Department of Biological Science, University of Toronto Scarborough, Scarborough, Ontario, Canada
- Department of Ecological and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Belinda S W Chang
- Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada
- Department of Ecological and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
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4
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Hagen JFD, Roberts NS, Johnston RJ. The evolutionary history and spectral tuning of vertebrate visual opsins. Dev Biol 2023; 493:40-66. [PMID: 36370769 PMCID: PMC9729497 DOI: 10.1016/j.ydbio.2022.10.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Revised: 10/27/2022] [Accepted: 10/31/2022] [Indexed: 11/11/2022]
Abstract
Many animals depend on the sense of vision for survival. In eumetazoans, vision requires specialized, light-sensitive cells called photoreceptors. Light reaches the photoreceptors and triggers the excitation of light-detecting proteins called opsins. Here, we describe the story of visual opsin evolution from the ancestral bilaterian to the extant vertebrate lineages. We explain the mechanisms determining color vision of extant vertebrates, focusing on opsin gene losses, duplications, and the expression regulation of vertebrate opsins. We describe the sequence variation both within and between species that has tweaked the sensitivities of opsin proteins towards different wavelengths of light. We provide an extensive resource of wavelength sensitivities and mutations that have diverged light sensitivity in many vertebrate species and predict how these mutations were accumulated in each lineage based on parsimony. We suggest possible natural and sexual selection mechanisms underlying these spectral differences. Understanding how molecular changes allow for functional adaptation of animals to different environments is a major goal in the field, and therefore identifying mutations affecting vision and their relationship to photic selection pressures is imperative. The goal of this review is to provide a comprehensive overview of our current understanding of opsin evolution in vertebrates.
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Affiliation(s)
- Joanna F D Hagen
- Department of Biology, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD, 21218, USA
| | - Natalie S Roberts
- Department of Biology, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD, 21218, USA
| | - Robert J Johnston
- Department of Biology, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD, 21218, USA.
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5
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Ancient whale rhodopsin reconstructs dim-light vision over a major evolutionary transition: Implications for ancestral diving behavior. Proc Natl Acad Sci U S A 2022; 119:e2118145119. [PMID: 35759662 PMCID: PMC9271160 DOI: 10.1073/pnas.2118145119] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Cetaceans are fully aquatic mammals that descended from terrestrial ancestors, an iconic evolutionary transition characterized by adaptations for underwater foraging via breath-hold diving. Although the evolutionary history of this specialized behavior is challenging to reconstruct, coevolving sensory systems may offer valuable clues. The dim-light visual pigment, rhodopsin, which initiates phototransduction in the rod photoreceptors of the eye, has provided insight into the visual ecology of depth in several aquatic vertebrate lineages. Here, we use ancestral sequence reconstruction and protein resurrection experiments to quantify light-activation metrics in rhodopsin pigments from ancestors bracketing the cetacean terrestrial-to-aquatic transition. By comparing multiple reconstruction methods on a broadly sampled cetartiodactyl species tree, we generated highly robust ancestral sequence estimates. Our experimental results provide direct support for a blue-shift in spectral sensitivity along the branch separating cetaceans from terrestrial relatives. This blue-shift was 14 nm, resulting in a deep-sea signature (λmax = 486 nm) similar to many mesopelagic-dwelling fish. We also discovered that the decay rates of light-activated rhodopsin increased in ancestral cetaceans, which may indicate an accelerated dark adaptation response typical of deeper-diving mammals. Because slow decay rates are thought to help sequester cytotoxic photoproducts, this surprising result could reflect an ecological trade-off between rod photoprotection and dark adaptation. Taken together, these ancestral shifts in rhodopsin function suggest that some of the first fully aquatic cetaceans could dive into the mesopelagic zone (>200 m). Moreover, our reconstructions indicate that this behavior arose before the divergence of toothed and baleen whales.
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6
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Schott RK, Perez L, Kwiatkowski MA, Imhoff V, Gumm JM. Evolutionary analyses of visual opsin genes in frogs and toads: Diversity, duplication, and positive selection. Ecol Evol 2022; 12:e8595. [PMID: 35154658 PMCID: PMC8820127 DOI: 10.1002/ece3.8595] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Revised: 01/07/2022] [Accepted: 01/08/2022] [Indexed: 01/12/2023] Open
Abstract
Among major vertebrate groups, anurans (frogs and toads) are understudied with regard to their visual systems, and little is known about variation among species that differ in ecology. We sampled North American anurans representing diverse evolutionary and life histories that likely possess visual systems adapted to meet different ecological needs. Using standard molecular techniques, visual opsin genes, which encode the protein component of visual pigments, were obtained from anuran retinas. Additionally, we extracted the visual opsins from publicly available genome and transcriptome assemblies, further increasing the phylogenetic and ecological diversity of our dataset to 33 species in total. We found that anurans consistently express four visual opsin genes (RH1, LWS, SWS1, and SWS2, but not RH2) even though reported photoreceptor complements vary widely among species. The proteins encoded by these genes showed considerable sequence variation among species, including at sites known to shift the spectral sensitivity of visual pigments in other vertebrates and had conserved substitutions that may be related to dim-light adaptation. Using molecular evolutionary analyses of selection (dN/dS) we found significant evidence for positive selection at a subset of sites in the dim-light rod opsin gene RH1 and the long wavelength sensitive cone opsin LWS. The function of sites inferred to be under positive selection are largely unknown, but a few are likely to affect spectral sensitivity and other visual pigment functions based on proximity to previously identified sites in other vertebrates. We also found the first evidence of visual opsin duplication in an amphibian with the duplication of the LWS gene in the African bullfrog, which had distinct LWS copies on the sex chromosomes suggesting the possibility of sex-specific visual adaptation. Taken together, our results indicate that ecological factors, such as habitat and life history, as well as behavior, may be driving changes to anuran visual systems.
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Affiliation(s)
- Ryan K. Schott
- Department of BiologyYork UniversityTorontoOntarioCanada
- Department of Vertebrate ZoologyNational Museum of Natural HistorySmithsonian InstitutionWashingtonDistrict of ColumbiaUSA
| | - Leah Perez
- Department of BiologyStephen F. Austin State UniversityNacogdochesTexasUSA
| | | | - Vance Imhoff
- Southern Nevada Fish and Wildlife OfficeUS Fish and Wildlife ServiceLas VegasNevadaUSA
| | - Jennifer M. Gumm
- Department of BiologyStephen F. Austin State UniversityNacogdochesTexasUSA
- Ash Meadows Fish Conservation FacilityUS Fish and Wildlife ServiceAmargosa ValleyNevadaUSA
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7
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Van Nynatten A, Castiglione GM, de A Gutierrez E, Lovejoy NR, Chang BSW. Recreated Ancestral Opsin Associated with Marine to Freshwater Croaker Invasion Reveals Kinetic and Spectral Adaptation. Mol Biol Evol 2021; 38:2076-2087. [PMID: 33481002 PMCID: PMC8097279 DOI: 10.1093/molbev/msab008] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Rhodopsin, the light-sensitive visual pigment expressed in rod photoreceptors, is specialized for vision in dim-light environments. Aquatic environments are particularly challenging for vision due to the spectrally dependent attenuation of light, which can differ greatly in marine and freshwater systems. Among fish lineages that have successfully colonized freshwater habitats from ancestrally marine environments, croakers are known as highly visual benthic predators. In this study, we isolate rhodopsins from a diversity of freshwater and marine croakers and find that strong positive selection in rhodopsin is associated with a marine to freshwater transition in South American croakers. In order to determine if this is accompanied by significant shifts in visual abilities, we resurrected ancestral rhodopsin sequences and tested the experimental properties of ancestral pigments bracketing this transition using in vitro spectroscopic assays. We found the ancestral freshwater croaker rhodopsin is redshifted relative to its marine ancestor, with mutations that recapitulate ancestral amino acid changes along this transitional branch resulting in faster kinetics that are likely to be associated with more rapid dark adaptation. This could be advantageous in freshwater due to the redshifted spectrum and relatively narrow interface and frequent transitions between bright and dim-light environments. This study is the first to experimentally demonstrate that positively selected substitutions in ancestral visual pigments alter protein function to freshwater visual environments following a transition from an ancestrally marine state and provides insight into the molecular mechanisms underlying some of the physiological changes associated with this major habitat transition.
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Affiliation(s)
- Alexander Van Nynatten
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada.,Department of Biological Sciences, University of Toronto Scarborough, Scarborough, ON, Canada
| | - Gianni M Castiglione
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Eduardo de A Gutierrez
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Nathan R Lovejoy
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada.,Department of Biological Sciences, University of Toronto Scarborough, Scarborough, ON, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Belinda S W Chang
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada.,Centre for the Analysis of Genome Evolution and Function, University of Toronto, Toronto, ON, Canada
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8
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Northover DE, Shank SD, Liberles DA. Characterizing lineage-specific evolution and the processes driving genomic diversification in chordates. BMC Evol Biol 2020; 20:24. [PMID: 32046633 PMCID: PMC7011509 DOI: 10.1186/s12862-020-1585-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Accepted: 01/16/2020] [Indexed: 11/21/2022] Open
Abstract
Background Understanding the origins of genome content has long been a goal of molecular evolution and comparative genomics. By examining genome evolution through the guise of lineage-specific evolution, it is possible to make inferences about the evolutionary events that have given rise to species-specific diversification. Here we characterize the evolutionary trends found in chordate species using The Adaptive Evolution Database (TAED). TAED is a database of phylogenetically indexed gene families designed to detect episodes of directional or diversifying selection across chordates. Gene families within the database have been assessed for lineage-specific estimates of dN/dS and have been reconciled to the chordate species to identify retained duplicates. Gene families have also been mapped to the functional pathways and amino acid changes which occurred on high dN/dS lineages have been mapped to protein structures. Results An analysis of this exhaustive database has enabled a characterization of the processes of lineage-specific diversification in chordates. A pathway level enrichment analysis of TAED determined that pathways most commonly found to have elevated rates of evolution included those involved in metabolism, immunity, and cell signaling. An analysis of protein fold presence on proteins, after normalizing for frequency in the database, found common folds such as Rossmann folds, Jelly Roll folds, and TIM barrels were overrepresented on proteins most likely to undergo directional selection. A set of gene families which experience increased numbers of duplications within short evolutionary times are associated with pathways involved in metabolism, olfactory reception, and signaling. An analysis of protein secondary structure indicated more relaxed constraint in β-sheets and stronger constraint on alpha Helices, amidst a general preference for substitutions at exposed sites. Lastly a detailed analysis of the ornithine decarboxylase gene family, a key enzyme in the pathway for polyamine synthesis, revealed lineage-specific evolution along the lineage leading to Cetacea through rapid sequence evolution in a duplicate gene with amino acid substitutions causing active site rearrangement. Conclusion Episodes of lineage-specific evolution are frequent throughout chordate species. Both duplication and directional selection have played large roles in the evolution of the phylum. TAED is a powerful tool for facilitating this understanding of lineage-specific evolution.
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Affiliation(s)
- David E Northover
- Department of Biology and Center for Computational Genetics and Genomics, Temple University, Philadelphia, PA, 19122, USA
| | - Stephen D Shank
- Department of Biology and Center for Computational Genetics and Genomics, Temple University, Philadelphia, PA, 19122, USA
| | - David A Liberles
- Department of Biology and Center for Computational Genetics and Genomics, Temple University, Philadelphia, PA, 19122, USA. .,Department of Molecular Biology, University of Wyoming, Laramie, WY, 82071, USA.
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9
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Van Nynatten A, Janzen FH, Brochu K, Maldonado-Ocampo JA, Crampton WGR, Chang BSW, Lovejoy NR. To see or not to see: molecular evolution of the rhodopsin visual pigment in neotropical electric fishes. Proc Biol Sci 2019; 286:20191182. [PMID: 31288710 DOI: 10.1098/rspb.2019.1182] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Functional variation in rhodopsin, the dim-light-specialized visual pigment, frequently occurs in species inhabiting light-limited environments. Variation in visual function can arise through two processes: relaxation of selection or adaptive evolution improving photon detection in a given environment. Here, we investigate the molecular evolution of rhodopsin in Gymnotiformes, an order of mostly nocturnal South American fishes that evolved sophisticated electrosensory capabilities. Our initial sequencing revealed a mutation associated with visual disease in humans. As these fishes are thought to have poor vision, this would be consistent with a possible sensory trade-off between the visual system and a novel electrosensory system. To investigate this, we surveyed rhodopsin from 147 gymnotiform species, spanning the order, and analysed patterns of molecular evolution. In contrast with our expectation, we detected strong selective constraint in gymnotiform rhodopsin, with rates of non-synonymous to synonymous substitutions lower in gymnotiforms than in other vertebrate lineages. In addition, we found evidence for positive selection on the branch leading to gymnotiforms and on a branch leading to a clade of deep-channel specialized gymnotiform species. We also found evidence that deleterious effects of a human disease-associated substitution are likely to be masked by epistatic substitutions at nearby sites. Our results suggest that rhodopsin remains an important component of the gymnotiform sensory system alongside electrolocation, and that photosensitivity of rhodopsin is well adapted for vision in dim-light environments.
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Affiliation(s)
- Alexander Van Nynatten
- 1 Department of Cell and Systems Biology, University of Toronto , Toronto, Ontario , Canada M5S 3G5.,2 Department of Biological Sciences, University of Toronto Scarborough , Toronto, Ontario , Canada M1C 1A4
| | - Francesco H Janzen
- 3 Department of Biology, University of Ottawa , Ottawa, Ontario , Canada K1N 6N5.,4 Canadian Museum of Nature , Ottawa, Ontario , Canada K1P 6P4
| | - Kristen Brochu
- 5 Department of Entomology, Penn State University , University Park, Pennsylvania 16802 USA
| | - Javier A Maldonado-Ocampo
- 6 Laboratorio de Ictiología, Unidad de Ecología y Sistemática-UNESIS, Departamento de Biología, Facultad de Ciencias, Pontificia Universidad Javeriana , Bogotá , Colombia
| | - William G R Crampton
- 7 Department of Biology, University of Central Florida , Orlando, FL 32816 , USA
| | - Belinda S W Chang
- 1 Department of Cell and Systems Biology, University of Toronto , Toronto, Ontario , Canada M5S 3G5.,8 Department of Ecology and Evolutionary Biology, University of Toronto , Toronto, Ontario , Canada M5S 3B2.,9 Centre for the Analysis of Genome Evolution and Function, University of Toronto , Toronto, Ontario , Canada M5S 3B2
| | - Nathan R Lovejoy
- 1 Department of Cell and Systems Biology, University of Toronto , Toronto, Ontario , Canada M5S 3G5.,2 Department of Biological Sciences, University of Toronto Scarborough , Toronto, Ontario , Canada M1C 1A4.,8 Department of Ecology and Evolutionary Biology, University of Toronto , Toronto, Ontario , Canada M5S 3B2
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10
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Gutierrez EDA, Castiglione GM, Morrow JM, Schott RK, Loureiro LO, Lim BK, Chang BSW. Functional Shifts in Bat Dim-Light Visual Pigment Are Associated with Differing Echolocation Abilities and Reveal Molecular Adaptation to Photic-Limited Environments. Mol Biol Evol 2019; 35:2422-2434. [PMID: 30010964 DOI: 10.1093/molbev/msy140] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Bats are excellent models for studying the molecular basis of sensory adaptation. In Chiroptera, a sensory trade-off has been proposed between the visual and auditory systems, though the extent of this association has yet to be fully examined. To investigate whether variation in visual performance is associated with echolocation, we experimentally assayed the dim-light visual pigment rhodopsin from bat species with differing echolocation abilities. While spectral tuning properties were similar among bats, we found that the rate of decay of their light-activated state was significantly slower in a nonecholocating bat relative to species that use distinct echolocation strategies, consistent with a sensory trade-off hypothesis. We also found that these rates of decay were remarkably slower compared with those of other mammals, likely indicating an adaptation to dim light. To examine whether functional changes in rhodopsin are associated with shifts in selection intensity upon bat Rh1 sequences, we implemented selection analyses using codon-based likelihood clade models. While no shifts in selection were identified in response to diverse echolocation abilities of bats, we detected a significant increase in the intensity of evolutionary constraint accompanying the diversification of Chiroptera. Taken together, this suggests that substitutions that modulate the stability of the light-activated rhodopsin state were likely maintained through intensified constraint after bats diversified, being finely tuned in response to novel sensory specializations. Our study demonstrates the power of combining experimental and computational approaches for investigating functional mechanisms underlying the evolution of complex sensory adaptations.
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Affiliation(s)
- Eduardo de A Gutierrez
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Gianni M Castiglione
- Department of Cell and Systems Biology, University of Toronto, ON, Canada.,Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - James M Morrow
- Department of Cell and Systems Biology, University of Toronto, ON, Canada.,Centre of Forensic Sciences, Toronto, ON, Canada
| | - Ryan K Schott
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada.,Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
| | - Livia O Loureiro
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Burton K Lim
- Department of Natural History, Royal Ontario Museum, Toronto, ON, Canada
| | - Belinda S W Chang
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada.,Department of Cell and Systems Biology, University of Toronto, ON, Canada.,Centre for the Analysis of Genome Evolution and Function, University of Toronto, Toronto, ON, Canada
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11
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Castiglione GM, Chang BS. Functional trade-offs and environmental variation shaped ancient trajectories in the evolution of dim-light vision. eLife 2018; 7:35957. [PMID: 30362942 PMCID: PMC6203435 DOI: 10.7554/elife.35957] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Accepted: 09/09/2018] [Indexed: 12/11/2022] Open
Abstract
Trade-offs between protein stability and activity can restrict access to evolutionary trajectories, but widespread epistasis may facilitate indirect routes to adaptation. This may be enhanced by natural environmental variation, but in multicellular organisms this process is poorly understood. We investigated a paradoxical trajectory taken during the evolution of tetrapod dim-light vision, where in the rod visual pigment rhodopsin, E122 was fixed 350 million years ago, a residue associated with increased active-state (MII) stability but greatly diminished rod photosensitivity. Here, we demonstrate that high MII stability could have likely evolved without E122, but instead, selection appears to have entrenched E122 in tetrapods via epistatic interactions with nearby coevolving sites. In fishes by contrast, selection may have exploited these epistatic effects to explore alternative trajectories, but via indirect routes with low MII stability. Our results suggest that within tetrapods, E122 and high MII stability cannot be sacrificed-not even for improvements to rod photosensitivity.
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Affiliation(s)
- Gianni M Castiglione
- Department of Cell and Systems Biology, University of Toronto, Toronto, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Canada
| | - Belinda Sw Chang
- Department of Cell and Systems Biology, University of Toronto, Toronto, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Canada.,Centre for the Analysis of Genome Evolution and Function, University of Toronto, Toronto, Canada
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12
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Karagic N, Härer A, Meyer A, Torres‐Dowdall J. Heterochronic opsin expression due to early light deprivation results in drastically shifted visual sensitivity in a cichlid fish: Possible role of thyroid hormone signaling. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2018; 330:202-214. [DOI: 10.1002/jez.b.22806] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Revised: 04/30/2018] [Accepted: 05/03/2018] [Indexed: 11/07/2022]
Affiliation(s)
- Nidal Karagic
- Zoology and Evolutionary BiologyDepartment of BiologyUniversity of Konstanz Konstanz Germany
| | - Andreas Härer
- Zoology and Evolutionary BiologyDepartment of BiologyUniversity of Konstanz Konstanz Germany
| | - Axel Meyer
- Zoology and Evolutionary BiologyDepartment of BiologyUniversity of Konstanz Konstanz Germany
- Radcliffe Institute for Advanced StudyHarvard University Cambridge Massachusetts
| | - Julián Torres‐Dowdall
- Zoology and Evolutionary BiologyDepartment of BiologyUniversity of Konstanz Konstanz Germany
- ZukunftskollegUniversity of Konstanz Konstanz Germany
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13
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Dungan SZ, Chang BSW. Epistatic interactions influence terrestrial-marine functional shifts in cetacean rhodopsin. Proc Biol Sci 2018; 284:rspb.2016.2743. [PMID: 28250185 DOI: 10.1098/rspb.2016.2743] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2016] [Accepted: 02/03/2017] [Indexed: 12/12/2022] Open
Abstract
Like many aquatic vertebrates, whales have blue-shifting spectral tuning substitutions in the dim-light visual pigment, rhodopsin, that are thought to increase photosensitivity in underwater environments. We have discovered that known spectral tuning substitutions also have surprising epistatic effects on another function of rhodopsin, the kinetic rates associated with light-activated intermediates. By using absorbance spectroscopy and fluorescence-based retinal release assays on heterologously expressed rhodopsin, we assessed both spectral and kinetic differences between cetaceans (killer whale) and terrestrial outgroups (hippo, bovine). Mutation experiments revealed that killer whale rhodopsin is unusually resilient to pleiotropic effects on retinal release from key blue-shifting substitutions (D83N and A292S), largely due to a surprisingly specific epistatic interaction between D83N and the background residue, S299. Ancestral sequence reconstruction indicated that S299 is an ancestral residue that predates the evolution of blue-shifting substitutions at the origins of Cetacea. Based on these results, we hypothesize that intramolecular epistasis helped to conserve rhodopsin's kinetic properties while enabling blue-shifting spectral tuning substitutions as cetaceans adapted to aquatic environments. Trade-offs between different aspects of molecular function are rarely considered in protein evolution, but in cetacean and other vertebrate rhodopsins, may underlie multiple evolutionary scenarios for the selection of specific amino acid substitutions.
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Affiliation(s)
- Sarah Z Dungan
- Department Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2
| | - Belinda S W Chang
- Department Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2 .,Centre for the Analysis of Genome Evolution and Function, University of Toronto, Toronto, ON, Canada M5S 3B2.,Department Cell and Systems Biology, University of Toronto, Toronto, ON, Canada M5S 3G5
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14
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Castiglione GM, Schott RK, Hauser FE, Chang BSW. Convergent selection pressures drive the evolution of rhodopsin kinetics at high altitudes via nonparallel mechanisms. Evolution 2018; 72:170-186. [DOI: 10.1111/evo.13396] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 11/02/2017] [Indexed: 01/01/2023]
Affiliation(s)
- Gianni M. Castiglione
- Department of Cell & Systems Biology; University of Toronto; Toronto Ontario M5S 3G5 Canada
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto Ontario M5S 3B2 Canada
| | - Ryan K. Schott
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto Ontario M5S 3B2 Canada
| | - Frances E. Hauser
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto Ontario M5S 3B2 Canada
| | - Belinda S. W. Chang
- Department of Cell & Systems Biology; University of Toronto; Toronto Ontario M5S 3G5 Canada
- Department of Ecology & Evolutionary Biology; University of Toronto; Toronto Ontario M5S 3B2 Canada
- Centre for the Analysis of Genome Evolution and Function; University of Toronto; Toronto Ontario M5S 3B2 Canada
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15
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Hauzman E, Bonci DMO, Suárez-Villota EY, Neitz M, Ventura DF. Daily activity patterns influence retinal morphology, signatures of selection, and spectral tuning of opsin genes in colubrid snakes. BMC Evol Biol 2017; 17:249. [PMID: 29228925 PMCID: PMC5725783 DOI: 10.1186/s12862-017-1110-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Accepted: 12/06/2017] [Indexed: 11/10/2022] Open
Abstract
Background Morphological divergences of snake retinal structure point to complex evolutionary processes and adaptations. The Colubridae family has a remarkable variety of retinal structure that can range from all-cone and all-rod to duplex (cone/rod) retinas. To explore whether nocturnal versus diurnal activity is responsible for constraints on molecular evolution and plays a role in visual opsin spectral tuning of colubrids, we carried out molecular evolution analyses of the visual opsin genes LWS, RH1, and SWS1 from 17 species and performed morphological analyses. Results Phylogenetic reconstructions of the RH1 and LWS recovered major clades characterized by primarily diurnal or primarily nocturnal activity patterns, in contrast with the topology for SWS1, which is very similar to the species tree. We found stronger signals of purifying selection along diurnal and nocturnal lineages for RH1 and SWS1, respectively. A blue-shift of the RH1 spectral peak is associated with diurnal habits. Spectral tuning of cone opsins did not differ among diurnal and nocturnal species. Retinas of nocturnal colubrids had many rows of photoreceptor nuclei, with large numbers of rods, labeled by wheat germ agglutinin (WGA), and two types of cones: large cones sensitive to long/medium wavelengths (L/M) and small cones sensitive to ultra-violet/violet wavelengths (UV/VS). In contrast, retinas of diurnal species had only one row of photoreceptor nuclei, with four types of cones: large and double L/M cones, small UV/VS cones, and a second group of small cones, labeled by WGA. Conclusions For LWS gene, selection tests did not confirm different constraints related to activity pattern. For SWS1, stronger purifying selection in nocturnal lineages indicates divergent evolutionary pressures related to the activity pattern, and the importance of the short wavelength sensitivity at low light condition. Activity pattern has a clear influence on the signatures of selection and spectral tuning of RH1, with stronger purifying selection in diurnal lineages, which indicates selective pressure to preserve rhodopsin structure and function in pure-cone retinas. We suggest that the presence of four cone types in primarily diurnal colubrids might be related to the gain of color discrimination capacity. Electronic supplementary material The online version of this article (10.1186/s12862-017-1110-0) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- E Hauzman
- Departamento de Psicologia Experimental, Instituto de Psicologia, Universidade de São Paulo, Av. Professor Mello Moraes 1721 Bloco A Sala D9 - Butantã, São Paulo, SP, CEP 05508-030, Brazil. .,Instituto Israelita de Ensino e Pesquisa Albert Einstein, São Paulo, Brazil.
| | - D M O Bonci
- Departamento de Psicologia Experimental, Instituto de Psicologia, Universidade de São Paulo, Av. Professor Mello Moraes 1721 Bloco A Sala D9 - Butantã, São Paulo, SP, CEP 05508-030, Brazil.,Instituto Israelita de Ensino e Pesquisa Albert Einstein, São Paulo, Brazil
| | - E Y Suárez-Villota
- Instituto de Ciencias Marinas y Limnólogicas, Universidad Austral de Chile, Edificio Emilio Pugin, Campus Isla Teja S/N, 5110236, Valdivia, Chile.,Laboratório de Ecologia e Evolução, Instituto Butantan, São Paulo, Brazil
| | - M Neitz
- Department of Opthalmology, University of Washington, 750 Republican Street, Box 358058, Seattle, WA, 98109, USA
| | - D F Ventura
- Departamento de Psicologia Experimental, Instituto de Psicologia, Universidade de São Paulo, Av. Professor Mello Moraes 1721 Bloco A Sala D9 - Butantã, São Paulo, SP, CEP 05508-030, Brazil.,Instituto Israelita de Ensino e Pesquisa Albert Einstein, São Paulo, Brazil
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16
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Hauser FE, Ilves KL, Schott RK, Castiglione GM, López-Fernández H, Chang BSW. Accelerated Evolution and Functional Divergence of the Dim Light Visual Pigment Accompanies Cichlid Colonization of Central America. Mol Biol Evol 2017; 34:2650-2664. [PMID: 28957507 DOI: 10.1093/molbev/msx192] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Cichlids encompass one of the most diverse groups of fishes in South and Central America, and show extensive variation in life history, morphology, and colouration. While studies of visual system evolution in cichlids have focussed largely on the African rift lake species flocks, Neotropical cichlids offer a unique opportunity to investigate visual system evolution at broader temporal and geographic scales. South American cichlid colonization of Central America has likely promoted accelerated rates of morphological evolution in Central American lineages as they encountered reduced competition, renewed ecological opportunity, and novel aquatic habitats. To investigate whether such transitions have influenced molecular evolution of vision in Central American cichlids, we sequenced the dim-light rhodopsin gene in 101 Neotropical cichlid species, spanning the diversity of the clade. We find strong evidence for increased rates of evolution in Central American cichlid rhodopsin relative to South American lineages, and identify several sites under positive selection in rhodopsin that likely contribute to adaptation to different photic environments. We expressed a Neotropical cichlid rhodopsin protein invitro for the first time, and found that while its spectral tuning properties were characteristic of typical vertebrate rhodopsin pigments, the rate of decay of its active signalling form was much slower, consistent with dim light adaptation in other vertebrate rhodopsins. Using site-directed mutagenesis combined with spectroscopic assays, we found that a key amino acid substitution present in some Central American cichlids accelerates the rate of decay of active rhodopsin, which may mediate adaptation to clear water habitats.
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Affiliation(s)
- Frances E Hauser
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Katriina L Ilves
- Department of Natural History, Royal Ontario Museum, Toronto, ON, Canada
- Department of Biology, Pace University, New York, NY
| | - Ryan K Schott
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Gianni M Castiglione
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
| | - Hernán López-Fernández
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
- Department of Natural History, Royal Ontario Museum, Toronto, ON, Canada
| | - Belinda S W Chang
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
- Centre for the Analysis of Genome Evolution and Function, University of Toronto, Toronto, ON, Canada
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17
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Abstract
High-altitude environments present a range of biochemical and physiological challenges for organisms through decreases in oxygen, pressure, and temperature relative to lowland habitats. Protein-level adaptations to hypoxic high-altitude conditions have been identified in multiple terrestrial endotherms; however, comparable adaptations in aquatic ectotherms, such as fishes, have not been as extensively characterized. In enzyme proteins, cold adaptation is attained through functional trade-offs between stability and activity, often mediated by substitutions outside the active site. Little is known whether signaling proteins [e.g., G protein-coupled receptors (GPCRs)] exhibit natural variation in response to cold temperatures. Rhodopsin (RH1), the temperature-sensitive visual pigment mediating dim-light vision, offers an opportunity to enhance our understanding of thermal adaptation in a model GPCR. Here, we investigate the evolution of rhodopsin function in an Andean mountain catfish system spanning a range of elevations. Using molecular evolutionary analyses and site-directed mutagenesis experiments, we provide evidence for cold adaptation in RH1. We find that unique amino acid substitutions occur at sites under positive selection in high-altitude catfishes, located at opposite ends of the RH1 intramolecular hydrogen-bonding network. Natural high-altitude variants introduced into these sites via mutagenesis have limited effects on spectral tuning, yet decrease the stability of dark-state and light-activated rhodopsin, accelerating the decay of ligand-bound forms. As found in cold-adapted enzymes, this phenotype likely compensates for a cold-induced decrease in kinetic rates-properties of rhodopsin that mediate rod sensitivity and visual performance. Our results support a role for natural variation in enhancing the performance of GPCRs in response to cold temperatures.
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18
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Morrow JM, Castiglione GM, Dungan SZ, Tang PL, Bhattacharyya N, Hauser FE, Chang BSW. An experimental comparison of human and bovine rhodopsin provides insight into the molecular basis of retinal disease. FEBS Lett 2017; 591:1720-1731. [PMID: 28369862 DOI: 10.1002/1873-3468.12637] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 03/22/2017] [Accepted: 03/25/2017] [Indexed: 11/05/2022]
Abstract
Rhodopsin is the visual pigment that mediates dim-light vision in vertebrates and is a model system for the study of retinal disease. The majority of rhodopsin experiments are performed using bovine rhodopsin; however, recent evidence suggests that significant functional differences exist among mammalian rhodopsins. In this study, we identify differences in both thermal decay and light-activated retinal release rates between bovine and human rhodopsin and perform mutagenesis studies to highlight two clusters of substitutions that contribute to these differences. We also demonstrate that the retinitis pigmentosa-associated mutation G51A behaves differently in human rhodopsin compared to bovine rhodopsin and determine that the thermal decay rate of an ancestrally reconstructed mammalian rhodopsin displays an intermediate phenotype compared to the two extant pigments.
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Affiliation(s)
- James M Morrow
- Department of Cell and Systems Biology, University of Toronto, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Canada
| | | | - Sarah Z Dungan
- Department of Ecology and Evolutionary Biology, University of Toronto, Canada
| | - Portia L Tang
- Department of Cell and Systems Biology, University of Toronto, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Canada
| | | | - Frances E Hauser
- Department of Ecology and Evolutionary Biology, University of Toronto, Canada
| | - Belinda S W Chang
- Department of Cell and Systems Biology, University of Toronto, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Canada.,Centre for the Analysis of Genome Evolution and Function, University of Toronto, Canada
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19
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van Hazel I, Dungan SZ, Hauser FE, Morrow JM, Endler JA, Chang BSW. A comparative study of rhodopsin function in the great bowerbird (Ptilonorhynchus nuchalis): Spectral tuning and light-activated kinetics. Protein Sci 2016; 25:1308-18. [PMID: 26889650 DOI: 10.1002/pro.2902] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Revised: 02/16/2016] [Accepted: 02/16/2016] [Indexed: 12/18/2022]
Abstract
Rhodopsin is the visual pigment responsible for initiating the phototransduction cascade in vertebrate rod photoreceptors. Although well-characterized in a few model systems, comparative studies of rhodopsin function, particularly for nonmammalian vertebrates are comparatively lacking. Bowerbirds are rare among passerines in possessing a key substitution, D83N, at a site that is otherwise highly conserved among G protein-coupled receptors. While this substitution is present in some dim-light adapted vertebrates, often accompanying another unusual substitution, A292S, its functional relevance in birds is uncertain. To investigate functional effects associated with these two substitutions, we use the rhodopsin gene from the great bowerbird (Ptilonorhynchus nuchalis) as a background for site-directed mutagenesis, in vitro expression and functional characterization. We also mutated these sites in two additional rhodopsins that do not naturally possess N83, chicken and bovine, for comparison. Both sites were found to contribute to spectral blue-shifts, but had opposing effects on kinetic rates. Substitutions at site 83 were found to primarily affect the kinetics of light-activated rhodopsin, while substitutions at site 292 had a larger impact on spectral tuning. The contribution of substitutions at site 83 to spectral tuning in particular depended on genetic background, but overall, the effects of substitutions were otherwise surprisingly additive, and the magnitudes of functional shifts were roughly similar across all three genetic backgrounds. By employing a comparative approach with multiple species, our study provides new insight into the joint impact of sites 83 and 292 on rhodopsin structure-function as well as their evolutionary significance for dim-light vision across vertebrates.
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Affiliation(s)
- Ilke van Hazel
- Department of Ecology and Evolutionary Biology, University of Toronto, Canada
| | - Sarah Z Dungan
- Department of Ecology and Evolutionary Biology, University of Toronto, Canada
| | - Frances E Hauser
- Department of Ecology and Evolutionary Biology, University of Toronto, Canada
| | - James M Morrow
- Department of Cell and Systems Biology, University of Toronto, Canada
| | - John A Endler
- Centre for Integrative Ecology, Deakin University, Australia
| | - Belinda S W Chang
- Department of Ecology and Evolutionary Biology, University of Toronto, Canada.,Department of Cell and Systems Biology, University of Toronto, Canada.,Centre for the Analysis of Genome Evolution and Function, University of Toronto, Canada
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20
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Comparative sequence analyses of rhodopsin and RPE65 reveal patterns of selective constraint across hereditary retinal disease mutations. Vis Neurosci 2016; 33:e002. [DOI: 10.1017/s0952523815000322] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractRetinitis pigmentosa (RP) comprises several heritable diseases that involve photoreceptor, and ultimately retinal, degeneration. Currently, mutations in over 50 genes have known links to RP. Despite advances in clinical characterization, molecular characterization of RP remains challenging due to the heterogeneous nature of causal genes, mutations, and clinical phenotypes. In this study, we compiled large datasets of two important visual genes associated with RP: rhodopsin, which initiates the phototransduction cascade, and the retinoid isomerase RPE65, which regenerates the visual cycle. We used a comparative evolutionary approach to investigate the relationship between interspecific sequence variation and pathogenic mutations that lead to degenerative retinal disease. Using codon-based likelihood methods, we estimated evolutionary rates (dN/dS) across both genes in a phylogenetic context to investigate differences between pathogenic and nonpathogenic amino acid sites. In both genes, disease-associated sites showed significantly lower evolutionary rates compared to nondisease sites, and were more likely to occur in functionally critical areas of the proteins. The nature of the dataset (e.g., vertebrate or mammalian sequences), as well as selection of pathogenic sites, affected the differences observed between pathogenic and nonpathogenic sites. Our results illustrate that these methods can serve as an intermediate step in understanding protein structure and function in a clinical context, particularly in predicting the relative pathogenicity (i.e., functional impact) of point mutations and their downstream phenotypic effects. Extensions of this approach may also contribute to current methods for predicting the deleterious effects of candidate mutations and to the identification of protein regions under strong constraint where we expect pathogenic mutations to occur.
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21
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Bickelmann C, Morrow JM, Du J, Schott RK, van Hazel I, Lim S, Müller J, Chang BSW. The molecular origin and evolution of dim-light vision in mammals. Evolution 2015; 69:2995-3003. [PMID: 26536060 DOI: 10.1111/evo.12794] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Revised: 09/23/2015] [Accepted: 09/27/2015] [Indexed: 01/19/2023]
Abstract
The nocturnal origin of mammals is a longstanding hypothesis that is considered instrumental for the evolution of endothermy, a potential key innovation in this successful clade. This hypothesis is primarily based on indirect anatomical inference from fossils. Here, we reconstruct the evolutionary history of rhodopsin--the vertebrate visual pigment mediating the first step in phototransduction at low-light levels--via codon-based model tests for selection, combined with gene resurrection methods that allow for the study of ancient proteins. Rhodopsin coding sequences were reconstructed for three key nodes: Amniota, Mammalia, and Theria. When expressed in vitro, all sequences generated stable visual pigments with λMAX values similar to the well-studied bovine rhodopsin. Retinal release rates of mammalian and therian ancestral rhodopsins, measured via fluorescence spectroscopy, were significantly slower than those of the amniote ancestor, indicating altered molecular function possibly related to nocturnality. Positive selection along the therian branch suggests adaptive evolution in rhodopsin concurrent with therian ecological diversification events during the Mesozoic that allowed for an exploration of the environment at varying light levels.
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Affiliation(s)
- Constanze Bickelmann
- Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, 10115, Berlin, Germany.
| | - James M Morrow
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, M5S 3G5, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Jing Du
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Ryan K Schott
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Ilke van Hazel
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Steve Lim
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, M5S 3G5, Canada
| | - Johannes Müller
- Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, 10115, Berlin, Germany
| | - Belinda S W Chang
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, M5S 3G5, Canada. .,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada. .,Centre for the Analysis of Genome Evolution and Function, Toronto, ON, M5S 3B2, Canada.
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22
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Dungan SZ, Kosyakov A, Chang BS. Spectral Tuning of Killer Whale (Orcinus orca) Rhodopsin: Evidence for Positive Selection and Functional Adaptation in a Cetacean Visual Pigment. Mol Biol Evol 2015; 33:323-36. [DOI: 10.1093/molbev/msv217] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
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23
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Morrow JM, Chang BSW. Comparative Mutagenesis Studies of Retinal Release in Light-Activated Zebrafish Rhodopsin Using Fluorescence Spectroscopy. Biochemistry 2015; 54:4507-18. [PMID: 26098991 DOI: 10.1021/bi501377b] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Rhodopsin is the visual pigment responsible for initiating scotopic (dim-light) vision in vetebrates. Once activated by light, release of all-trans-retinal from rhodopsin involves hydrolysis of the Schiff base linkage, followed by dissociation of retinal from the protein moiety. This kinetic process has been well studied in model systems such as bovine rhodopsin, but not in rhodopsins from cold-blooded animals, where physiological temperatures can vary considerably. Here, we characterize the rate of retinal release from light-activated rhodopsin in an ectotherm, zebrafish (Danio rerio), demonstrating in a fluorescence assay that this process occurs more than twice as fast as bovine rhodopsin at similar temperatures in 0.1% dodecyl maltoside. Using site-directed mutagenesis, we found that differences in retinal release rates can be attributed to a series of variable residues lining the retinal channel in three key structural motifs: an opening in metarhodopsin II between transmembrane helix 5 (TM5) and TM6, in TM3 near E122, and in the "retinal plug" formed by extracellular loop 2 (EL2). The majority of these sites are more proximal to the β-ionone ring of retinal than the Schiff base, indicating their influence on retinal release is more likely due to steric effects during retinal dissociation, rather than alterations to Schiff base stability. An Arrhenius plot of zebrafish rhodopsin was consistent with this model, inferring that the activation energy for Schiff base hydrolysis is similar to that of bovine rhodopsin. Functional variation at key sites identified in this study is consistent with the idea that retinal release might be an adaptive property of rhodopsin in vertebrates. Our study is one of the few investigating a nonmammalian rhodopsin, which will help establish a better understanding of the molecular mechanisms contributing to vision in cold-blooded vertebrates.
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24
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Bloch NI, Morrow JM, Chang BSW, Price TD. SWS2 visual pigment evolution as a test of historically contingent patterns of plumage color evolution in warblers. Evolution 2015; 69:341-56. [PMID: 25496318 DOI: 10.1111/evo.12572] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Accepted: 11/19/2014] [Indexed: 12/22/2022]
Abstract
Distantly related clades that occupy similar environments may differ due to the lasting imprint of their ancestors-historical contingency. The New World warblers (Parulidae) and Old World warblers (Phylloscopidae) are ecologically similar clades that differ strikingly in plumage coloration. We studied genetic and functional evolution of the short-wavelength-sensitive visual pigments (SWS2 and SWS1) to ask if altered color perception could contribute to the plumage color differences between clades. We show SWS2 is short-wavelength shifted in birds that occupy open environments, such as finches, compared to those in closed environments, including warblers. Phylogenetic reconstructions indicate New World warblers were derived from a finch-like form that colonized from the Old World 15-20 Ma. During this process, the SWS2 gene accumulated six substitutions in branches leading to New World warblers, inviting the hypothesis that passage through a finch-like ancestor resulted in SWS2 evolution. In fact, we show spectral tuning remained similar across warblers as well as the finch ancestor. Results reject the hypothesis of historical contingency based on opsin spectral tuning, but point to evolution of other aspects of visual pigment function. Using the approach outlined here, historical contingency becomes a generally testable theory in systems where genotype and phenotype can be connected.
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Affiliation(s)
- Natasha I Bloch
- Department of Ecology & Evolution, University of Chicago, Chicago, 60637.
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McGowen MR, Gatesy J, Wildman DE. Molecular evolution tracks macroevolutionary transitions in Cetacea. Trends Ecol Evol 2014; 29:336-46. [DOI: 10.1016/j.tree.2014.04.001] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Revised: 04/02/2014] [Accepted: 04/03/2014] [Indexed: 10/25/2022]
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Schott RK, Refvik SP, Hauser FE, López-Fernández H, Chang BSW. Divergent positive selection in rhodopsin from lake and riverine cichlid fishes. Mol Biol Evol 2014; 31:1149-65. [PMID: 24509690 DOI: 10.1093/molbev/msu064] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Studies of cichlid evolution have highlighted the importance of visual pigment genes in the spectacular radiation of the African rift lake cichlids. Recent work, however, has also provided strong evidence for adaptive diversification of riverine cichlids in the Neotropics, which inhabit environments of markedly different spectral properties from the African rift lakes. These ecological and/or biogeographic differences may have imposed divergent selective pressures on the evolution of the cichlid visual system. To test these hypotheses, we investigated the molecular evolution of the dim-light visual pigment, rhodopsin. We sequenced rhodopsin from Neotropical and African riverine cichlids and combined these data with published sequences from African cichlids. We found significant evidence for positive selection using random sites codon models in all cichlid groups, with the highest levels in African lake cichlids. Tests using branch-site and clade models that partitioned the data along ecological (lake, river) and/or biogeographic (African, Neotropical) boundaries found significant evidence of divergent selective pressures among cichlid groups. However, statistical comparisons among these models suggest that ecological, rather than biogeographic, factors may be responsible for divergent selective pressures that have shaped the evolution of the visual system in cichlids. We found that branch-site models did not perform as well as clade models for our data set, in which there was evidence for positive selection in the background. One of our most intriguing results is that the amino acid sites found to be under positive selection in Neotropical and African lake cichlids were largely nonoverlapping, despite falling into the same three functional categories: spectral tuning, retinal uptake/release, and rhodopsin dimerization. Taken together, these results would imply divergent selection across cichlid clades, but targeting similar functions. This study highlights the importance of molecular investigations of ecologically important groups and the flexibility of clade models in explicitly testing ecological hypotheses.
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Affiliation(s)
- Ryan K Schott
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
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Meredith RW, Gatesy J, Emerling CA, York VM, Springer MS. Rod monochromacy and the coevolution of cetacean retinal opsins. PLoS Genet 2013; 9:e1003432. [PMID: 23637615 PMCID: PMC3630094 DOI: 10.1371/journal.pgen.1003432] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Accepted: 02/15/2013] [Indexed: 01/02/2023] Open
Abstract
Cetaceans have a long history of commitment to a fully aquatic lifestyle that extends back to the Eocene. Extant species have evolved a spectacular array of adaptations in conjunction with their deployment into a diverse array of aquatic habitats. Sensory systems are among those that have experienced radical transformations in the evolutionary history of this clade. In the case of vision, previous studies have demonstrated important changes in the genes encoding rod opsin (RH1), short-wavelength sensitive opsin 1 (SWS1), and long-wavelength sensitive opsin (LWS) in selected cetaceans, but have not examined the full complement of opsin genes across the complete range of cetacean families. Here, we report protein-coding sequences for RH1 and both color opsin genes (SWS1, LWS) from representatives of all extant cetacean families. We examine competing hypotheses pertaining to the timing of blue shifts in RH1 relative to SWS1 inactivation in the early history of Cetacea, and we test the hypothesis that some cetaceans are rod monochomats. Molecular evolutionary analyses contradict the "coastal" hypothesis, wherein SWS1 was pseudogenized in the common ancestor of Cetacea, and instead suggest that RH1 was blue-shifted in the common ancestor of Cetacea before SWS1 was independently knocked out in baleen whales (Mysticeti) and in toothed whales (Odontoceti). Further, molecular evidence implies that LWS was inactivated convergently on at least five occasions in Cetacea: (1) Balaenidae (bowhead and right whales), (2) Balaenopteroidea (rorquals plus gray whale), (3) Mesoplodon bidens (Sowerby's beaked whale), (4) Physeter macrocephalus (giant sperm whale), and (5) Kogia breviceps (pygmy sperm whale). All of these cetaceans are known to dive to depths of at least 100 m where the underwater light field is dim and dominated by blue light. The knockout of both SWS1 and LWS in multiple cetacean lineages renders these taxa rod monochromats, a condition previously unknown among mammalian species.
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Affiliation(s)
- Robert W. Meredith
- Department of Biology, University of California Riverside, Riverside, California, United States of America
- Department of Biology and Molecular Biology, Montclair State University, Montclair, New Jersey, United States of America
| | - John Gatesy
- Department of Biology, University of California Riverside, Riverside, California, United States of America
| | - Christopher A. Emerling
- Department of Biology, University of California Riverside, Riverside, California, United States of America
| | - Vincent M. York
- Department of Biology, University of California Riverside, Riverside, California, United States of America
- Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America
| | - Mark S. Springer
- Department of Biology, University of California Riverside, Riverside, California, United States of America
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Niemiller ML, Fitzpatrick BM, Shah P, Schmitz L, Near TJ. Evidence for repeated loss of selective constraint in rhodopsin of amblyopsid cavefishes (Teleostei: Amblyopsidae). Evolution 2012; 67:732-48. [PMID: 23461324 DOI: 10.1111/j.1558-5646.2012.01822.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The genetic mechanisms underlying regressive evolution-the degeneration or loss of a derived trait--are largely unknown, particularly for complex structures such as eyes in cave organisms. In several eyeless animals, the visual photoreceptor rhodopsin appears to have retained functional amino acid sequences. Hypotheses to explain apparent maintenance of function include weak selection for retention of light-sensing abilities and its pleiotropic roles in circadian rhythms and thermotaxis. In contrast, we show that there has been repeated loss of functional constraint of rhodopsin in amblyopsid cavefishes, as at least three cave lineages have independently accumulated unique loss-of-function mutations over the last 10.3 Mya. Although several cave lineages still possess functional rhodopsin, they exhibit increased rates of nonsynonymous mutations that have greater effect on the structure and function of rhodopsin compared to those in surface lineages. These results indicate that functionality of rhodopsin has been repeatedly lost in amblyopsid cavefishes. The presence of a functional copy of rhodopsin in some cave lineages is likely explained by stochastic accumulation of mutations following recent subterranean colonization.
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Affiliation(s)
- Matthew L Niemiller
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996, USA.
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Weadick CJ, Loew ER, Rodd FH, Chang BSW. Visual Pigment Molecular Evolution in the Trinidadian Pike Cichlid (Crenicichla frenata): A Less Colorful World for Neotropical Cichlids? Mol Biol Evol 2012; 29:3045-60. [DOI: 10.1093/molbev/mss115] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Functional characterization of the rod visual pigment of the echidna (Tachyglossus aculeatus), a basal mammal. Vis Neurosci 2012; 29:211-7. [PMID: 22874131 DOI: 10.1017/s0952523812000223] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Monotremes are the most basal egg-laying mammals comprised of two extant genera, which are largely nocturnal. Visual pigments, the first step in the sensory transduction cascade in photoreceptors of the eye, have been examined in a variety of vertebrates, but little work has been done to study the rhodopsin of monotremes. We isolated the rhodopsin gene of the nocturnal short-beaked echidna (Tachyglossus aculeatus) and expressed and functionally characterized the protein in vitro. Three mutants were also expressed and characterized: N83D, an important site for spectral tuning and metarhodopsin kinetics, and two sites with amino acids unique to the echidna (T158A and F169A). The λ(max) of echidna rhodopsin (497.9 ± 1.1 nm) did not vary significantly in either T158A (498.0 ± 1.3 nm) or F169A (499.4 ± 0.1 nm) but was redshifted in N83D (503.8 ± 1.5 nm). Unlike other mammalian rhodopsins, echidna rhodopsin did react when exposed to hydroxylamine, although not as fast as cone opsins. The retinal release rate of light-activated echidna rhodopsin, as measured by fluorescence spectroscopy, had a half-life of 9.5 ± 2.6 min-1, which is significantly shorter than that of bovine rhodopsin. The half-life of the N83D mutant was 5.1 ± 0.1 min-1, even shorter than wild type. Our results show that with respect to hydroxylamine sensitivity and retinal release, the wild-type echidna rhodopsin displays major differences to all previously characterized mammalian rhodopsins and appears more similar to other nonmammalian vertebrate rhodopsins such as chicken and anole. However, our N83D mutagenesis results suggest that this site may mediate adaptation in the echidna to dim light environments, possibly via increased stability of light-activated intermediates. This study is the first characterization of a rhodopsin from a most basal mammal and indicates that there might be more functional variation in mammalian rhodopsins than previously assumed.
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Miyagi R, Terai Y, Aibara M, Sugawara T, Imai H, Tachida H, Mzighani SI, Okitsu T, Wada A, Okada N. Correlation between nuptial colors and visual sensitivities tuned by opsins leads to species richness in sympatric Lake Victoria cichlid fishes. Mol Biol Evol 2012; 29:3281-96. [PMID: 22617953 DOI: 10.1093/molbev/mss139] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Reproductive isolation that prevents interspecific hybridization between closely related coexisting species maintains sympatric species diversity. One of the reproductive isolations is mate choice based on color signals (breeding color perceived by color vision). This is well known in several animal taxa, yet little is known about its genetic and molecular mechanism. Lake Victoria cichlid fishes are thought to be an example of sympatric species diversity. In the species inhabiting different light environments in rocky shore, speciation by sensory drive through color signals has been proposed by analyses of the long wavelength-sensitive (LWS) opsin gene and the male nuptial coloration. However, the genetic and molecular mechanism of how diversity of sympatric species occurring in the same habitat is maintained remains unknown. To address this issue, we determined nucleotide sequences of eight opsins of six sympatric species collected from a sandy-muddy shore--an ideal model system for studying sympatric species. Among eight opsins, the LWS and RH1 alleles were diversified and one particular allele is dominant or fixed in each species, and we propose that this is due to natural selection. The functions of their LWS alleles were also diversified as shown by absorption measurements of reconstituted visual pigments. To analyze the relationship between nuptial coloration and the absorption of LWS pigments, we systematically evaluated and defined nuptial coloration. We showed that the coloration was species specific with respect to hue and significantly differentiated by the index values of hue (dominant wavelength: λ(d)). The λ(d) value of the male nuptial coloration correlated with the absorption of LWS pigments from all the species, suggesting that reproductive isolation through mate choice using color signals may prevent sympatric interspecific hybridization, thereby maintaining the species diversity in sympatric species in Lake Victoria.
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Affiliation(s)
- Ryutaro Miyagi
- Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, Japan
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