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Zimmer AM. Ammonia excretion by the fish gill: discoveries and ideas that shaped our current understanding. J Comp Physiol B 2024:10.1007/s00360-024-01561-5. [PMID: 38849577 DOI: 10.1007/s00360-024-01561-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Revised: 03/06/2024] [Accepted: 05/15/2024] [Indexed: 06/09/2024]
Abstract
The fish gill serves many physiological functions, among which is the excretion of ammonia, the primary nitrogenous waste in most fishes. Although it is the end-product of nitrogen metabolism, ammonia serves many physiological functions including acting as an acid equivalent and as a counter-ion in mechanisms of ion regulation. Our current understanding of the mechanisms of ammonia excretion have been influenced by classic experimental work, clever mechanistic approaches, and modern molecular and genetic techniques. In this review, I will overview the history of the study of ammonia excretion by the gills of fishes, highlighting the important advancements that have shaped this field with a nearly 100-year history. The developmental and evolutionary implications of an ammonia and gill-dominated nitrogen regulation strategy in most fishes will also be discussed. Throughout the review, I point to areas in which more work is needed to push forward this field of research that continues to produce novel insights and discoveries that will undoubtedly shape our overall understanding of fish physiology.
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Affiliation(s)
- Alex M Zimmer
- Department of Biological Sciences, University of New Brunswick, 100 Tucker Park Road, Saint John, Saint John, New Brunswick, E2L 4L5, Canada.
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2
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Williamson G, Harris T, Bizior A, Hoskisson PA, Pritchard L, Javelle A. Biological ammonium transporters: evolution and diversification. FEBS J 2024. [PMID: 38265636 DOI: 10.1111/febs.17059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 12/14/2023] [Accepted: 01/09/2024] [Indexed: 01/25/2024]
Abstract
Although ammonium is the preferred nitrogen source for microbes and plants, in animal cells it is a toxic product of nitrogen metabolism that needs to be excreted. Thus, ammonium movement across biological membranes, whether for uptake or excretion, is a fundamental and ubiquitous biological process catalysed by the superfamily of the Amt/Mep/Rh transporters. A remarkable feature of the Amt/Mep/Rh family is that they are ubiquitous and, despite sharing low amino acid sequence identity, are highly structurally conserved. Despite sharing a common structure, these proteins have become involved in a diverse range of physiological process spanning all domains of life, with reports describing their involvement in diverse biological processes being published regularly. In this context, we exhaustively present their range of biological roles across the domains of life and after explore current hypotheses concerning their evolution to help to understand how and why the conserved structure fulfils diverse physiological functions.
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Affiliation(s)
- Gordon Williamson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Thomas Harris
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Adriana Bizior
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Paul Alan Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Leighton Pritchard
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | - Arnaud Javelle
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, UK
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3
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Ridgway MR, Tunnah L, Bernier NJ, Wilson JM, Wright PA. Novel spikey ionocytes are regulated by cortisol in the skin of an amphibious fish. Proc Biol Sci 2021; 288:20212324. [PMID: 34933603 PMCID: PMC8692953 DOI: 10.1098/rspb.2021.2324] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Accepted: 11/26/2021] [Indexed: 12/24/2022] Open
Abstract
Cortisol is a major osmoregulatory hormone in fishes. Cortisol acts upon the gills, the primary site of ionoregulation, through modifications to specialized ion-transporting cells called ionocytes. We tested the hypothesis that cortisol also acts as a major regulator of skin ionocyte remodelling in the amphibious mangrove rivulus (Kryptolebias marmoratus) when gill function ceases during the water-to-land transition. When out of water, K. marmoratus demonstrated a robust cortisol response, which was linked with the remodelling of skin ionocytes to increase cell cross-sectional area and Na+-K+-ATPase (NKA) content, but not when cortisol synthesis was chemically inhibited by metyrapone. Additionally, we discovered a novel morphology of skin-specific ionocyte that are spikey with multiple cell processes. Spikey ionocytes increased in density, cell cross-sectional area and NKA content during air exposure, but not in metyrapone-treated fish. Our findings demonstrate that skin ionocyte remodelling during the water-to-land transition in amphibious fish is regulated by cortisol, the same hormone that regulates gill ionocyte remodelling in salinity-challenged teleosts, suggesting conserved hormonal function across diverse environmental disturbances and organs in fishes.
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Affiliation(s)
- Megan R. Ridgway
- Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Louise Tunnah
- Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Nicholas J. Bernier
- Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Jonathan M. Wilson
- Department of Biology, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5, Canada
| | - Patricia A. Wright
- Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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4
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Vanderwolf KJ, Kyle CJ, Faure PA, McAlpine DF, Davy CM. Skin pH varies among bat species and seasons and between wild and captive bats. CONSERVATION PHYSIOLOGY 2021; 9:coab088. [PMID: 34925845 PMCID: PMC8672241 DOI: 10.1093/conphys/coab088] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 07/09/2021] [Accepted: 11/01/2021] [Indexed: 06/14/2023]
Abstract
Skin is a key aspect of the immune system in the defence against pathogens. Skin pH regulates the activity of enzymes produced both by hosts and by microbes on host skin, thus implicating pH in disease susceptibility. Skin pH varies inter- and intra-specifically and is influenced by a variety of intrinsic and extrinsic variables. Increased skin alkalinity is associated with a predisposition to cutaneous infections in humans and dogs, and inter-specific and inter-individual variation in skin pH is implicated in differential susceptibility to some skin diseases. The cutaneous pH of bats has not been characterized but is postulated to play a role in susceptibility to white-nose syndrome (WNS), a fungal infection that has decimated several Nearctic bat species. We used non-invasive probes to measure the pH of bat flight membranes in five species with differing susceptibility to WNS. Skin pH ranged from 4.67 to 8.59 and varied among bat species, geographic locations, body parts, age classes, sexes and seasons. Wild Eptesicus fuscus were consistently more acidic than wild Myotis lucifugus, Myotis leibii and Perimyotis subflavus. Juvenile bats had more acidic skin than adults during maternity season but did not differ during swarming. Male M. lucifugus were more acidic than females during maternity season, yet this trend reversed during swarming. Bat skin was more acidic in summer compared to winter, a pattern also reported in humans. Skin pH was more acidic in captive than wild E. fuscus, suggesting environmental impacts on skin pH. The pH of roosting substrates affects skin pH in captive bats and may partially explain seasonal patterns in wild bats that use different roost types across seasons. Future research on the influence of pH on microbial pathogenic factors and skin barrier function may provide valuable insights on new therapeutic targets for treating bat skin conditions.
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Affiliation(s)
- Karen J Vanderwolf
- Corresponding author: Environmental and Life Sciences Program, Trent University, 1600 West Bank Dr., Peterborough, K9L 0G2, Canada.
| | - Christopher J Kyle
- Environmental and Life Sciences Program, Trent University, 1600 West Bank Dr., Peterborough, K9L 0G2, Ontario, Canada
- Forensic Science Department, Trent University, 1600 West Bank Dr, Peterborough, K9L 0G2, Ontario, Canada
- Natural Resources DNA Profiling and Forensics Center, Trent University, 1600 West Bank Dr, Peterborough, K9L 0G2, Ontario, Canada
| | - Paul A Faure
- Department of Psychology, Neuroscience & Behaviour, McMaster University, 1280 Main Street West, Hamilton, L8S 4K1, Ontario, Canada
| | - Donald F McAlpine
- Department of Natural History, New Brunswick Museum, 277 Douglas Ave, Saint John, E2K 1E5, New Brunswick, Canada
| | - Christina M Davy
- Environmental and Life Sciences Program, Trent University, 1600 West Bank Dr., Peterborough, K9L 0G2, Ontario, Canada
- Wildlife Research and Monitoring Section, Ontario Ministry of Northern Development, Mines, Natural Resources and Forestry, 1600 West Bank Dr, Peterborough, K9L 0G2, Ontario, Canada
- Current affiliation: Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, K1S 5B6, Ontario, Canada
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5
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Wright PA. Cutaneous respiration and osmoregulation in amphibious fishes. Comp Biochem Physiol A Mol Integr Physiol 2021; 253:110866. [DOI: 10.1016/j.cbpa.2020.110866] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 12/03/2020] [Accepted: 12/04/2020] [Indexed: 01/06/2023]
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6
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Dong YW, Blanchard TS, Noll A, Vasquez P, Schmitz J, Kelly SP, Wright PA, Whitehead A. Genomic and physiological mechanisms underlying skin plasticity during water to air transition in an amphibious fish. J Exp Biol 2021; 224:jeb235515. [PMID: 33328287 PMCID: PMC7860121 DOI: 10.1242/jeb.235515] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Accepted: 12/09/2020] [Indexed: 12/24/2022]
Abstract
The terrestrial radiation of vertebrates required changes in skin that resolved the dual demands of maintaining a mechanical and physiological barrier while also facilitating ion and gas transport. Using the amphibious killifish Kryptolebias marmoratus, we found that transcriptional regulation of skin morphogenesis was quickly activated upon air exposure (1 h). Rapid regulation of cell-cell adhesion complexes and pathways that regulate stratum corneum formation was consistent with barrier function and mechanical reinforcement. Unique blood vessel architecture and regulation of angiogenesis likely supported cutaneous respiration. Differences in ionoregulatory transcripts and ionocyte morphology were correlated with differences in salinity acclimation and resilience to air exposure. Evolutionary analyses reinforced the adaptive importance of these mechanisms. We conclude that rapid plasticity of barrier, respiratory and ionoregulatory functions in skin evolved to support the amphibious lifestyle of K. marmoratus; similar processes may have facilitated the terrestrial radiation of other contemporary and ancient fishes.
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Affiliation(s)
- Yun-Wei Dong
- The Key Laboratory of Mariculture, Ministry of Education, Fisheries College, Ocean University of China, Qingdao, People's Republic of China
| | - Tessa S Blanchard
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1
| | - Angela Noll
- Primate Genetics Laboratory, German Primate Center (DPZ), Leibniz Institute for Primate Research, 37077 Göttingen, Germany
| | - Picasso Vasquez
- Department of Environmental Toxicology, University of California Davis, Davis, CA 95616, USA
| | - Juergen Schmitz
- Institute of Experimental Pathology, Center for Molecular Biology of Inflammation (ZMBE), University of Münster, 48149 Münster, Germany
| | - Scott P Kelly
- Department of Biology, York University, Toronto, ON, Canada, M3J 1P3
| | - Patricia A Wright
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1
| | - Andrew Whitehead
- Department of Environmental Toxicology, Center for Population Biology, Coastal and Marine Sciences Institute, University of California Davis, Davis, CA 95616, USA
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7
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Livingston MD, Bhargav VV, Turko AJ, Wilson JM, Wright PA. Widespread use of emersion and cutaneous ammonia excretion in Aplocheiloid killifishes. Proc Biol Sci 2018; 285:rspb.2018.1496. [PMID: 30111602 DOI: 10.1098/rspb.2018.1496] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Accepted: 07/17/2018] [Indexed: 11/12/2022] Open
Abstract
The invasion of land required amphibious fishes to evolve new strategies to avoid toxic ammonia accumulation in the absence of water flow over the gills. We investigated amphibious behaviour and nitrogen excretion strategies in six phylogenetically diverse Aplocheiloid killifishes (Anablepsoides hartii, Cynodonichthys hildebrandi, Rivulus cylindraceus, Kryptolebias marmoratus, Fundulopanchax gardneri, and Aplocheilus lineatus) in order to determine if a common strategy evolved. All species voluntarily emersed (left water) over several days, and also in response to environmental stressors (low O2, high temperature). All species were ammoniotelic in water and released gaseous ammonia (NH3 volatilization) during air exposure as the primary route for nitrogen excretion. Metabolic depression, urea synthesis, and/or ammonia accumulation during air exposure were not common strategies used by these species. Immunostaining revealed the presence of ammonia-transporting Rhesus proteins (Rhcg1 and Rhcg2) in the skin of all six species, indicating a shared mechanism for ammonia volatilization. We also found Rhcg in the skin of several other fully aquatic fishes, implying that cutaneous ammonia excretion is not exclusive to amphibious fishes. Overall, our results demonstrate that similar nitrogen excretion strategies while out of water were used by all killifish species tested; possibly the result of shared ancestral amphibious traits, phenotypic convergence, or a combination of both.
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Affiliation(s)
- Michael D Livingston
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada N1G 2W1
| | - Vikram V Bhargav
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada N1G 2W1
| | - Andy J Turko
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada N1G 2W1
| | - Jonathan M Wilson
- Department of Biology, Wilfrid Laurier University, ON, Canada N2 L 3C5
| | - Patricia A Wright
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada N1G 2W1
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8
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Heffell Q, Turko AJ, Wright PA. Plasticity of skin water permeability and skin thickness in the amphibious mangrove rivulus Kryptolebias marmoratus. J Comp Physiol B 2017; 188:305-314. [PMID: 28940028 DOI: 10.1007/s00360-017-1123-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 08/29/2017] [Accepted: 09/11/2017] [Indexed: 01/29/2023]
Abstract
The skin of amphibious fishes is a multipurpose organ, important for gas and ion exchange and nitrogen excretion when fish are out of water (emersed). We tested the hypothesis that skin permeability is altered to maintain water balance through changes in water permeability and skin thickness during salinity acclimation and/or when fish emerse, using the euryhaline, amphibious fish Kryptolebias marmoratus as a model. We first recorded the behaviour of fish out of water to determine which part of the cutaneous surface was in contact with the substrate. Fish spent about 70% of their time on their ventral surface when out of water. Osmotic permeability of the skin was assessed in fish acclimated to 0.3 or 45‰ using 3H2O fluxes in an in vitro micro-Ussing chamber setup. In freshwater-acclimated fish, 3H2O influx across the skin was significantly higher compared to hypersaline-acclimated fish, with no significant changes in efflux. Prolonged emersion (7 days) resulted in an increase in skin 3H2O influx, but not efflux in fish acclimated to a moist 45‰ substrate. In a separate experiment, dorsal epidermal skin thickness increased while the ventral dermis thickness decreased in fish emersed for over a week. However, there was no link between regional skin thickness and water flux in our experiments. Taken together, these findings suggest that K. marmoratus alter skin permeability to maximize water uptake while emersed in hypersaline conditions, adjustments that probably help them survive months of emersion during the dry season when drinking to replace water loss is not possible.
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Affiliation(s)
- Quentin Heffell
- Department of Integrative Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada
| | - Andy J Turko
- Department of Integrative Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada
| | - Patricia A Wright
- Department of Integrative Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada.
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9
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Wright PA, Turko AJ. Amphibious fishes: evolution and phenotypic plasticity. ACTA ACUST UNITED AC 2017; 219:2245-59. [PMID: 27489213 DOI: 10.1242/jeb.126649] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2016] [Accepted: 06/29/2016] [Indexed: 12/25/2022]
Abstract
Amphibious fishes spend part of their life in terrestrial habitats. The ability to tolerate life on land has evolved independently many times, with more than 200 extant species of amphibious fishes spanning 17 orders now reported. Many adaptations for life out of water have been described in the literature, and adaptive phenotypic plasticity may play an equally important role in promoting favourable matches between the terrestrial habitat and behavioural, physiological, biochemical and morphological characteristics. Amphibious fishes living at the interface of two very different environments must respond to issues relating to buoyancy/gravity, hydration/desiccation, low/high O2 availability, low/high CO2 accumulation and high/low NH3 solubility each time they traverse the air-water interface. Here, we review the literature for examples of plastic traits associated with the response to each of these challenges. Because there is evidence that phenotypic plasticity can facilitate the evolution of fixed traits in general, we summarize the types of investigations needed to more fully determine whether plasticity in extant amphibious fishes can provide indications of the strategies used during the evolution of terrestriality in tetrapods.
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Affiliation(s)
- Patricia A Wright
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
| | - Andy J Turko
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
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10
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Blair S, Wilkie M, Edwards S. Rh glycoprotein immunoreactivity in the skin and its role in extrabranchial ammonia excretion by the sea lamprey (Petromyzon marinus) in fresh water. CAN J ZOOL 2017. [DOI: 10.1139/cjz-2016-0120] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Aquatic organisms employ various strategies to excrete ammonia across the gills, skin, and (or) renal routes. During three different stages of their life cycle, we hypothesized that the basal vertebrate sea lamprey (Petromyzon marinus L., 1758) used the skin as a route for ammonia excretion. Measurements of ammonia excretion using divided flux chambers revealed that extrabranchial sites (skin plus renal) of ammonia excretion were quantitatively more important in larval sea lampreys, but following metamorphosis, the gills became the dominant route of excretion in juvenile sea lampreys. Despite the greater relative importance of the skin in the larval stage, Rh glycoprotein isoforms Rhbg, Rhcg1, and Rhcg2 were detected in the skin in all three sea lamprey life stages examined, but the patterns of expression were dependent on the life stage. We conclude that, during the relatively sedentary filter-feeding larval stage, extrabranchial routes play an equally important role as the gill in facilitating ammonia excretion. However, the gills by virtue of their extensive branchial vasculature become the dominant route of ammonia excretion following metamorphosis because of the need to offload greater amounts of ammonia arising from higher rates of basal ammonia production and the potential to excrete higher amounts of ammonia following ingestion of protein-rich blood in the parasitic stage.
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Affiliation(s)
- S.D. Blair
- Department of Biology, Appalachian State University, Boone, NC 28608, USA
- Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada
| | - M.P. Wilkie
- Department of Biology, Wilfrid Laurier University, Waterloo, ON N2L 3C5, Canada
- Department of Biology, Mount Allison University, Sackville, NB E4L 1G7, Canada
| | - S.L. Edwards
- Department of Biology, Appalachian State University, Boone, NC 28608, USA
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11
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Turko AJ, Wright PA. Evolution, ecology and physiology of amphibious killifishes (Cyprinodontiformes). JOURNAL OF FISH BIOLOGY 2015; 87:815-835. [PMID: 26299792 DOI: 10.1111/jfb.12758] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Accepted: 06/24/2015] [Indexed: 06/04/2023]
Abstract
The order Cyprinodontiformes contains an exceptional diversity of amphibious taxa, including at least 34 species from six families. These cyprinodontiforms often inhabit intertidal or ephemeral habitats characterized by low dissolved oxygen or otherwise poor water quality, conditions that have been hypothesized to drive the evolution of terrestriality. Most of the amphibious species are found in the Rivulidae, Nothobranchiidae and Fundulidae. It is currently unclear whether the pattern of amphibiousness observed in the Cyprinodontiformes is the result of repeated, independent evolutions, or stems from an amphibious common ancestor. Amphibious cyprinodontiforms leave water for a variety of reasons: some species emerse only briefly, to escape predation or capture prey, while others occupy ephemeral habitats by living for months at a time out of water. Fishes able to tolerate months of emersion must maintain respiratory gas exchange, nitrogen excretion and water and salt balance, but to date knowledge of the mechanisms that facilitate homeostasis on land is largely restricted to model species. This review synthesizes the available literature describing amphibious lifestyles in cyprinodontiforms, compares the behavioural and physiological strategies used to exploit the terrestrial environment and suggests directions and ideas for future research.
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Affiliation(s)
- A J Turko
- Department of Integrative Biology, University of Guelph, 488 Gordon Street, Guelph, ON, N1G 2W1, Canada
| | - P A Wright
- Department of Integrative Biology, University of Guelph, 488 Gordon Street, Guelph, ON, N1G 2W1, Canada
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12
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Avise JC, Tatarenkov A. Population genetics and evolution of the mangrove rivulus Kryptolebias marmoratus, the world's only self-fertilizing hermaphroditic vertebrate. JOURNAL OF FISH BIOLOGY 2015; 87:519-538. [PMID: 26223378 DOI: 10.1111/jfb.12741] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 06/09/2015] [Indexed: 05/20/2023]
Abstract
The mangrove rivulus, Kryptolebias marmoratus (Rivulidae, Cyprinodontiformes), is phylogenetically embedded within a large clade of oviparous (egg laying) and otherwise mostly gonochoristic (separate sex) killifish species in the circumtropical suborder Aplocheiloidei. It is unique in its reproductive mode: K. marmoratus is essentially the world's only vertebrate species known to engage routinely in self-fertilization as part of a mixed-mating strategy of selfing plus occasional outcrossing with gonochoristic males. This unique form of procreation has profound population-genetic and evolutionary-genetic consequences that are the subject of this review.
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Affiliation(s)
- J C Avise
- Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, U.S.A
| | - A Tatarenkov
- Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, U.S.A
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13
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Larsen EH, Deaton LE, Onken H, O'Donnell M, Grosell M, Dantzler WH, Weihrauch D. Osmoregulation and Excretion. Compr Physiol 2014; 4:405-573. [DOI: 10.1002/cphy.c130004] [Citation(s) in RCA: 127] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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14
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Chew SF, Ip YK. Excretory nitrogen metabolism and defence against ammonia toxicity in air-breathing fishes. JOURNAL OF FISH BIOLOGY 2014; 84:603-38. [PMID: 24438022 DOI: 10.1111/jfb.12279] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
With the development of air-breathing capabilities, some fishes can emerge from water, make excursions onto land or even burrow into mud during droughts. Air-breathing fishes have modified gill morphology and morphometry and accessory breathing organs, which would tend to reduce branchial ammonia excretion. As ammonia is toxic, air-breathing fishes, especially amphibious ones, are equipped with various strategies to ameliorate ammonia toxicity during emersion or ammonia exposure. These strategies can be categorized into (1) enhancement of ammonia excretion and reduction of ammonia entry, (2) conversion of ammonia to a less toxic product for accumulation and subsequent excretion, (3) reduction of ammonia production and avoidance of ammonia accumulation and (4) tolerance of ammonia at cellular and tissue levels. Active ammonia excretion, operating in conjunction with lowering of ambient pH and reduction in branchial and cutaneous NH₃ permeability, is theoretically the most effective strategy to maintain low internal ammonia concentrations. NH₃ volatilization involves the alkalization of certain epithelial surfaces and requires mechanisms to prevent NH₃ back flux. Urea synthesis is an energy-intensive process and hence uncommon among air-breathing teleosts. Aestivating African lungfishes detoxify ammonia to urea and the accumulated urea is excreted following arousal. Reduction in ammonia production is achieved in some air-breathing fishes through suppression of amino acid catabolism and proteolysis, or through partial amino acid catabolism leading to alanine formation. Others can slow down ammonia accumulation through increased glutamine synthesis in the liver and muscle. Yet, some others develop high tolerance of ammonia at cellular and tissue levels, including tissues in the brain. In summary, the responses of air-breathing fishes to ameliorate ammonia toxicity are many and varied, determined by the behaviour of the species and the nature of the environment in which it lives.
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Affiliation(s)
- S F Chew
- Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Republic of Singapore
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15
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The skin of fish as a transport epithelium: a review. J Comp Physiol B 2013; 183:877-91. [DOI: 10.1007/s00360-013-0761-4] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Accepted: 04/23/2013] [Indexed: 01/17/2023]
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16
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Cooper CA, Wilson JM, Wright PA. Marine, freshwater and aerially acclimated mangrove rivulus (Kryptolebias marmoratus) use different strategies for cutaneous ammonia excretion. Am J Physiol Regul Integr Comp Physiol 2013; 304:R599-612. [PMID: 23389109 DOI: 10.1152/ajpregu.00228.2012] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Rhesus (Rh) glycoproteins are ammonia gas (NH(3)) channels known to be involved in ammonia transport in animals. Because of the different osmoregulatory and ionoregulatory challenges faced by teleost fishes in marine and freshwater (FW) environments, we hypothesized that ammonia excretion strategies would differ between environments. Also, we hypothesized that cutaneous NH(3) volatilization in air-acclimated fish is facilitated by base secretion. To test these hypotheses, we used the skin of the euryhaline amphibious mangrove rivulus (Kryptolebias marmoratus). The skin excretes ammonia and expresses Rh glycoproteins. Serosal-to-mucosal cutaneous ammonia flux was saturable (0-16 mmol/l ammonia, K(m) of 6.42 mmol/l). In FW, ammonia excretion increased in response to low mucosal pH but decreased with pharmacological inhibition of Na(+)/H(+) exchangers (NHE) and H(+) ATPase. Conversely, in brackish water (BW), lowering the mucosal pH significantly decreased ammonia excretion. Inhibitors of NHE also decreased ammonia excretion in BW fish. Immunofluorescence microscopy demonstrated that both the Rh isoform, Rhcg1, and NHE3 proteins colocalized in Na(+)/K(+) ATPase expressing mitochondrion-rich cells in the gills, kidney, and skin. We propose that the mechanisms of cutaneous ammonia excretion in FW K. marmoratus are consistent with the model for branchial ammonia excretion in FW teleost fish. NH(4)(+) excretion appeared to play a stronger role in BW. NH(4)(+) excretion in BW may be facilitated by apical NHE and/or diffuse through paracellular pathways. In aerially acclimated fish, inhibition of NHE and H(+) ATPase, but not the Cl(-)/HCO(3)(-) exchanger, significantly affected cutaneous surface pH, suggesting that direct base excretion is not critical for NH(3) volatilization. Overall, K. marmoratus use different strategies for excreting ammonia in three different environments, FW, BW, and air, and Rh glycoproteins and NHE are integral to all.
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Dhiyebi HA, O'Donnell MJ, Wright PA. Water chemistry in the microenvironment of rainbow trout Oncorhynchus mykiss embryos is affected by development, the egg capsule and crowding. JOURNAL OF FISH BIOLOGY 2013; 82:444-457. [PMID: 23398061 DOI: 10.1111/j.1095-8649.2012.03491.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The hypothesis tested was that embryonic metabolism affects the water chemistry in the boundary layer. In addition, embryo crowding would further compound the metabolic effect on the water chemistry in the boundary layer. As development progressed, the magnitude of the boundary layer gradients for O(2) and pH, but not for NH4(+), increased. The presence of the egg capsule hindered the diffusion of O(2) into and H(+) and NH4(+) out of the embryo. The magnitude of the O(2), pH and NH4(+) boundary layer gradient was significantly increased when embryos were surrounded by either sham embryos or live embryos. The majority of this crowding effect on embryo boundary layers was due to changes in water flow rather than due to metabolism directly. These results clearly show that the microenvironment adjacent to the developing rainbow trout Oncorhynchus mykiss embryo becomes more stagnant as development progresses in the presence of the egg capsule and is further intensified with embryo crowding.
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Affiliation(s)
- H A Dhiyebi
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada.
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Taylor DS. Twenty-four years in the mud: what have we learned about the natural history and ecology of the mangrove rivulus, Kryptolebias marmoratus? Integr Comp Biol 2012; 52:724-36. [PMID: 22576816 PMCID: PMC3501094 DOI: 10.1093/icb/ics062] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Although first described in 1880, Kryptolebias marmoratus avoided scientific scrutiny until 1961, when it was identified as the only known selfing hermaphroditic vertebrate. The subsequent intense interest in this fish as a laboratory animal, continuing to this day, might explain the paucity of wild collections, but our collective knowledge now suggests that the inherent difficulty of wild collection is more a matter of "looking in all the wrong places." Long thought to be rare in the mangroves, and it is rare in certain human-impacted habitats, K. marmoratus can be quite abundant, but in microhabitats not typically targeted by ichthyologists: ephemeral pools at higher elevations in the swamp, crab burrows, and other fossorial or even terrestrial haunts. Field studies of this enigmatic fish have revealed almost amphibious behaviors. During emersion these fish tolerate extended dry periods. In water, they are exposed to temperature extremes, high levels of hydrogen sulfide, and depleted dissolved oxygen. Finally, their catholic diet and a geographically variable sex life completes a portrait of an unusual animal. A clearer picture is emerging of adult life, with initial population density estimates now known and some indication of high population turnover in burrows, but juvenile habitat and adult oviposition sites remain unknown.
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Affiliation(s)
- D. Scott Taylor
- Brevard County Environmentally Endangered Lands Program, 91 East Drive, Melbourne, FL 32904, USA
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Wright PA. Environmental physiology of the mangrove rivulus, Kryptolebias marmoratus, a cutaneously breathing fish that survives for weeks out of water. Integr Comp Biol 2012; 52:792-800. [PMID: 22693260 PMCID: PMC3501097 DOI: 10.1093/icb/ics091] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The mangrove rivulus (Kryptolebias marmoratus) is an excellent model species for understanding the physiological mechanisms that fish use in coping with extreme environmental conditions, particularly cutaneous exchange during prolonged exposure to air. Their ability to self-fertilize and produce highly homozygous lineages provides the potential for examining environmental influences on structures and related functions without the complications of genetic variation. Over the past 10 years or so, we have gained a broader understanding of the mechanisms K. marmoratus use to maintain homeostasis when out of water for days to weeks. Gaseous exchange occurs across the skin, as dramatic remodeling of the gill reduces its effective surface area for exchange. Ionoregulation and osmoregulation are maintained in air by exchanging Na(+), Cl(-), and H(2)O across skin that contains a rich population of ionocytes. Ammonia excretion occurs in part by cutaneous NH(3) volatilization facilitated by ammonia transporters on the surface of the epidermis. Finally, new evidence indicates that cutaneous angiogenesis occurs when K. marmoratus are emersed for a week, suggesting a higher rate of blood flow to surface vessels. Taken together, these and other findings demonstrate that the skin of K. marmoratus takes on all the major functions attributed to fish gills, allowing them to move between aquatic and terrestrial environments with ease. Future studies should focus on variation in response to environmental changes between homozygous lineages to identify the genetic underpinnings of physiological responses.
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Affiliation(s)
- Patricia A Wright
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada N1G 2W1.
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Ellison A, Wright P, Taylor DS, Cooper C, Regan K, Currie S, Consuegra S. Environmental diel variation, parasite loads, and local population structuring of a mixed-mating mangrove fish. Ecol Evol 2012; 2:1682-95. [PMID: 22957172 PMCID: PMC3434939 DOI: 10.1002/ece3.289] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2012] [Revised: 05/06/2012] [Accepted: 05/08/2012] [Indexed: 11/13/2022] Open
Abstract
Genetic variation within populations depends on population size, spatial structuring, and environmental variation, but is also influenced by mating system. Mangroves are some of the most productive and threatened ecosystems on earth and harbor a large proportion of species with mixed-mating (self-fertilization and outcrossing). Understanding population structuring in mixed-mating species is critical for conserving and managing these complex ecosystems. Kryptolebias marmoratus is a unique mixed-mating vertebrate inhabiting mangrove swamps under highly variable tidal regimes and environmental conditions. We hypothesized that geographical isolation and ecological pressures influence outcrossing rates and genetic diversity, and ultimately determine the local population structuring of K. marmoratus. By comparing genetic variation at 32 microsatellites, diel fluctuations of environmental parameters, and parasite loads among four locations with different degrees of isolation, we found significant differences in genetic diversity and genotypic composition but little evidence of isolation by distance. Locations also differed in environmental diel fluctuation and parasite composition. Our results suggest that mating system, influenced by environmental instability and parasites, underpins local population structuring of K. marmoratus. More generally, we discuss how the conservation of selfing species inhabiting mangroves and other biodiversity hotspots may benefit from knowledge of mating strategies and population structuring at small spatial scales.
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Affiliation(s)
- Amy Ellison
- IBERS, Aberystwyth UniversityPenglais Campus, Aberystwyth SY23 3DA, United Kingdom
| | - Patricia Wright
- Department of Integrative Biology, University of GuelphGuelph, ON, N1G 2W1, Canada
| | - D Scott Taylor
- Brevard County Environmentally Endangered Lands ProgramMelbourne, Florida 32904
| | - Chris Cooper
- Department of Integrative Biology, University of GuelphGuelph, ON, N1G 2W1, Canada
| | - Kelly Regan
- Department of Integrative Biology, University of GuelphGuelph, ON, N1G 2W1, Canada
| | - Suzie Currie
- Department of Biology, Mount Allison UniversitySackville, NB, E4L 1G7, Canada
| | - Sofia Consuegra
- IBERS, Aberystwyth UniversityPenglais Campus, Aberystwyth SY23 3DA, United Kingdom
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21
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Wright PA, Wood CM. Seven things fish know about ammonia and we don't. Respir Physiol Neurobiol 2012; 184:231-40. [PMID: 22910326 DOI: 10.1016/j.resp.2012.07.003] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2012] [Revised: 07/03/2012] [Accepted: 07/04/2012] [Indexed: 01/01/2023]
Abstract
In this review we pose the following seven questions related to ammonia and fish that represent gaps in our knowledge. 1. How is ammonia excretion linked to sodium uptake in freshwater fish? 2. How much does branchial ammonia excretion in seawater teleosts depend on Rhesus (Rh) glycoprotein-mediated NH(3) diffusion? 3. How do fish maintain ammonia excretion rates if branchial surface area is reduced or compromised? 4. Why does high environmental ammonia change the transepithelial potential across the gills? 5. Does high environmental ammonia increase gill surface area in ammonia tolerant fish but decrease gill surface area in ammonia intolerant fish? 6. How does ammonia contribute to ventilatory control? 7. What do Rh proteins do when they are not transporting ammonia? Mini reviews on each topic, which are able to present only partial answers to each question at present, are followed by further questions and/or suggestions for research approaches targeted to uncover answers.
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Affiliation(s)
- Patricia A Wright
- Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.
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Wilkie MP, Pamenter ME, Duquette S, Dhiyebi H, Sangha N, Skelton G, Smith MD, Buck LT. The relationship between NMDA receptor function and the high ammonia tolerance of anoxia-tolerant goldfish. ACTA ACUST UNITED AC 2012; 214:4107-20. [PMID: 22116753 DOI: 10.1242/jeb.057513] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Acute ammonia toxicity in vertebrates is thought to be characterized by a cascade of deleterious events resembling those associated with anoxic/ischemic injury in the central nervous system. A key event is the over-stimulation of neuronal N-methyl-D-aspartate (NMDA) receptors, which leads to excitotoxic cell death. The similarity between the responses to acute ammonia toxicity and anoxia suggests that anoxia-tolerant animals such as the goldfish (Carassius auratus Linnaeus) may also be ammonia tolerant. To test this hypothesis, the responses of goldfish were compared with those of the anoxia-sensitive rainbow trout (Oncorhynchus mykiss Walbaum) during exposure to high external ammonia (HEA). Acute toxicity tests revealed that goldfish are ammonia tolerant, with 96 h median lethal concentration (LC(50)) values of 199 μmol l(-1) and 4132 μmol l(-1) for NH(3) and total ammonia ([T(Amm)]=[NH(3)]+[NH(4)(+)]), respectively. These values were ~5-6 times greater than corresponding NH(3) and T(Amm) LC(50) values measured in rainbow trout. Further, the goldfish readily coped with chronic exposure to NH(4)Cl (3-5 mmol l(-1)) for 5 days, despite 6-fold increases in plasma [T] to ~1300 μmol l(-1) and 3-fold increases in brain [T(Amm)] to 6700 μmol l(-1). Muscle [T(Amm)] increased by almost 8-fold from ~900 μmol kg(-1) wet mass (WM) to greater than 7000 μmol kg(-1) WM by 48 h, and stabilized. Although urea excretion rates (J(Urea)) increased by 2-3-fold during HEA, the increases were insufficient to offset the inhibition of ammonia excretion that occurred, and increases in urea were not observed in the brain or muscle. There was a marked increase in brain glutamine concentration at HEA, from ~3000 μmol kg(-1) WM to 15,000 μmol kg(-1) WM after 48 h, which is consistent with the hypothesis that glutamine production is associated with ammonia detoxification. Injection of the NMDA receptor antagonists MK801 (0.5-8 mg kg(-1)) or ethanol (1-8 mg kg(-1)) increased trout survival time by 1.5-2.0-fold during exposure to 2 mmol l(-1) ammonia, suggesting that excitotoxic cell death contributes to ammonia toxicity in this species. In contrast, similar doses of MK801 or ethanol had no effect on ammonia-challenged (8-9.5 mmol l(-1) T(Amm)) goldfish survival times, suggesting that greater resistance to excitotoxic cell death contributes to the high ammonia-tolerance of the goldfish. Whole-cell recordings measured in isolated brain slices of goldfish telencephalon during in vitro exposure to 5 mmol l(-1) or 10 mmol l(-1) T(Amm) reversibly potentiated NMDA receptor currents. This observation suggested that goldfish neurons may not be completely resistant to ammonia-induced excitotoxicity. Subsequent western blot and densitometric analyses revealed that NMDA receptor NR1 subunit abundance was 40-60% lower in goldfish exposed to 3-5 mmol l(-1) T(Amm) for 5 days, which was followed by a restoration of NR1 subunit abundance after 3 days recovery in ammonia-free water. We conclude that the goldfish brain may be protected from excitotoxicity by downregulating the abundance of functional NMDA receptors during periods when it experiences increased internal ammonia.
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Affiliation(s)
- Michael P Wilkie
- Department of Biology, Wilfrid Laurier University, Waterloo, ON, Canada.
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23
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Cutaneous vasoregulation during short- and long-term aerial acclimation in the amphibious mangrove rivulus, Kryptolebias marmoratus. Comp Biochem Physiol B Biochem Mol Biol 2012; 161:268-74. [DOI: 10.1016/j.cbpb.2011.12.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Revised: 12/05/2011] [Accepted: 12/05/2011] [Indexed: 11/22/2022]
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24
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Behaviour drives morphology: voluntary emersion patterns shape gill structure in genetically identical mangrove rivulus. Anim Behav 2011. [DOI: 10.1016/j.anbehav.2011.03.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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25
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LeBlanc DM, Wood CM, Fudge DS, Wright PA. A Fish Out of Water: Gill and Skin Remodeling Promotes Osmo- and Ionoregulation in the Mangrove KillifishKryptolebias marmoratus. Physiol Biochem Zool 2010; 83:932-49. [DOI: 10.1086/656307] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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26
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Ip YK, Chew SF. Ammonia production, excretion, toxicity, and defense in fish: a review. Front Physiol 2010; 1:134. [PMID: 21423375 PMCID: PMC3059970 DOI: 10.3389/fphys.2010.00134] [Citation(s) in RCA: 170] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2010] [Accepted: 09/06/2010] [Indexed: 12/20/2022] Open
Abstract
Many fishes are ammonotelic but some species can detoxify ammonia to glutamine or urea. Certain fish species can accumulate high levels of ammonia in the brain or defense against ammonia toxicity by enhancing the effectiveness of ammonia excretion through active NH4+transport, manipulation of ambient pH, or reduction in ammonia permeability through the branchial and cutaneous epithelia. Recent reports on ammonia toxicity in mammalian brain reveal the importance of permeation of ammonia through the blood-brain barrier and passages of ammonia and water through transporters in the plasmalemma of brain cells. Additionally, brain ammonia toxicity could be related to the passage of glutamine through the mitochondrial membranes into the mitochondrial matrix. On the other hand, recent reports on ammonia excretion in fish confirm the involvement of Rhesus glycoproteins in the branchial and cutaneous epithelia. Therefore, this review focuses on both the earlier literature and the up-to-date information on the problems and mechanisms concerning the permeation of ammonia, as NH(3), NH4+ or proton-neutral nitrogenous compounds, across mitochondrial membranes, the blood-brain barrier, the plasmalemma of neurons, and the branchial and cutaneous epithelia of fish. It also addresses how certain fishes with high ammonia tolerance defend against ammonia toxicity through the regulation of the permeation of ammonia and related nitrogenous compounds through various types of membranes. It is hoped that this review would revive the interests in investigations on the passage of ammonia through the mitochondrial membranes and the blood-brain barrier of ammonotelic fishes and fishes with high brain ammonia tolerance, respectively.
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Affiliation(s)
- Yuen K Ip
- Department of Biological Sciences, National University of Singapore Singapore, Republic of Singapore.
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27
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Tatarenkov A, Ring BC, Elder JF, Bechler DL, Avise JC. Genetic composition of laboratory stocks of the self-fertilizing fish Kryptolebias marmoratus: a valuable resource for experimental research. PLoS One 2010; 5:e12863. [PMID: 20877576 PMCID: PMC2943930 DOI: 10.1371/journal.pone.0012863] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2010] [Accepted: 08/24/2010] [Indexed: 11/19/2022] Open
Abstract
The hermaphroditic Mangrove Killifish, Kryptolebias marmoratus, is the world's only vertebrate that routinely self-fertilizes. As such, highly inbred and presumably isogenic "clonal" lineages of this androdioecious species have long been maintained in several laboratories and used in a wide variety of experiments that require genetically uniform vertebrate specimens. Here we conduct a genetic inventory of essentially all laboratory stocks of the Mangrove Killifish held worldwide. At 32 microsatellite loci, these stocks proved to show extensive interline differentiation as well as some intraline variation, much of which can be attributed to post-origin de novo mutations and/or to the segregation of polymorphisms from wild progenitors. Our genetic findings also document that many of the surveyed laboratory strains are not what they have been labeled, apparently due to the rather frequent mishandling or unintended mixing of various laboratory stocks over the years. Our genetic inventory should help to clarify much of this confusion about the clonal identities and genetic relationships of laboratory lines, and thereby help to rejuvenate interest in K. marmoratus as a reliable vertebrate model for experimental research that requires or can capitalize upon "clonal" replicate specimens.
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Affiliation(s)
- Andrey Tatarenkov
- Department of Ecology and Evolutionary Biology, University of California Irvine, Irvine, California, United States of America
| | - Brian C. Ring
- Department of Biology, Valdosta State University, Valdosta, Georgia, United States of America
| | - John F. Elder
- Department of Biology, Valdosta State University, Valdosta, Georgia, United States of America
| | - David L. Bechler
- Department of Biology, Valdosta State University, Valdosta, Georgia, United States of America
| | - John C. Avise
- Department of Ecology and Evolutionary Biology, University of California Irvine, Irvine, California, United States of America
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Wright PA, Wood CM. A new paradigm for ammonia excretion in aquatic animals: role of Rhesus(Rh) glycoproteins. J Exp Biol 2009; 212:2303-12. [DOI: 10.1242/jeb.023085] [Citation(s) in RCA: 283] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
SUMMARY
Ammonia excretion at the gills of fish has been studied for 80 years, but the mechanism(s) involved remain controversial. The relatively recent discovery of the ammonia-transporting function of the Rhesus (Rh) proteins, a family related to the Mep/Amt family of methyl ammonia and ammonia transporters in bacteria, yeast and plants, and the occurrence of these genes and glycosylated proteins in fish gills has opened a new paradigm. We provide background on the evolution and function of the Rh proteins, and review recent studies employing molecular physiology which demonstrate their important contribution to branchial ammonia efflux. Rhag occurs in red blood cells,whereas several isoforms of both Rhbg and Rhcg occur in many tissues. In the branchial epithelium, Rhcg appears to be localized in apical membranes and Rhbg in basolateral membranes. Their gene expression is upregulated during exposure to high environmental ammonia or internal ammonia infusion, and may be sensitive to synergistic stimulation by ammonia and cortisol. Rhcg in particular appears to be coupled to H+ excretion and Na+uptake mechanisms. We propose a new model for ammonia excretion in freshwater fish and its variable linkage to Na+ uptake and acid excretion. In this model, Rhag facilitates NH3 flux out of the erythrocyte, Rhbg moves it across the basolateral membrane of the branchial ionocyte, and an apical “Na+/NH +4 exchange complex” consisting of several membrane transporters (Rhcg, V-type H+-ATPase, Na+/H+ exchanger NHE-2 and/or NHE-3, Na+ channel) working together as a metabolon provides an acid trapping mechanism for apical excretion. Intracellular carbonic anhydrase(CA-2) and basolateral Na+/HCO –3cotransporter (NBC-1) and Na+/K+-ATPase play indirect roles. These mechanisms are normally superimposed on a substantial outward movement of NH3 by simple diffusion, which is probably dependent on acid trapping in boundary layer water by H+ ions created by the catalysed or non-catalysed hydration of expired metabolic CO2. Profitable areas for future investigation of Rh proteins in fish are highlighted: their involvement in the mechanism of ammonia excretion across the gills in seawater fish, their possible importance in ammonia excretion across the skin, their potential dual role as CO2 transporters,their responses to feeding, and their roles in early life stages prior to the full development of gills.
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Affiliation(s)
- Patricia A. Wright
- Department of Integrative Biology, University of Guelph, Guelph, ON, N1G 2W1,Canada
| | - Chris M. Wood
- Department of Biology, McMaster University, Hamilton, ON, L8S 4K1,Canada
- Division of Marine Biology and Fisheries, Rosenstiel School of Marine Atmospheric Science, University of Miami, Miami, FL 33149, USA
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29
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Weihrauch D, Wilkie MP, Walsh PJ. Ammonia and urea transporters in gills of fish and aquatic crustaceans. J Exp Biol 2009; 212:1716-30. [PMID: 19448081 DOI: 10.1242/jeb.024851] [Citation(s) in RCA: 184] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The diversity of mechanisms of ammonia and urea excretion by the gills and other epithelia of aquatic organisms, especially fish and crustaceans, has been studied for decades. Although the decades-old dogma of ;aquatic species excrete ammonia' still explains nitrogenous waste excretion for many species, it is clear that there are many mechanistic variations on this theme. Even within species that are ammonoteles, the process is not purely ;passive', often relying on the energizing effects of proton and sodium-potassium ATPases. Within the ammonoteles, Rh (Rhesus) proteins are beginning to emerge as vital ammonia conduits. Many fishes are also known to be capable of substantial synthesis and excretion of urea as a nitrogenous waste. In such species, members of the UT family of urea transporters have been identified as important players in urea transport across the gills. This review attempts to draw together recent information to update the mechanisms of ammonia and urea transport by the gills of aquatic species. Furthermore, we point out several potentially fruitful avenues for further research.
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Affiliation(s)
- Dirk Weihrauch
- Department of Biological Sciences, University of Manitoba, 190 Dysart Road, Winnipeg, MB, R3T 2N2 Canada
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30
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Hung CC, Nawata CM, Wood CM, Wright PA. Rhesus glycoprotein and urea transporter genes are expressed in early stages of development of rainbow trout (Oncorhynchus mykiss). JOURNAL OF EXPERIMENTAL ZOOLOGY. PART A, ECOLOGICAL GENETICS AND PHYSIOLOGY 2008; 309:262-8. [PMID: 18404668 DOI: 10.1002/jez.456] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2023]
Abstract
The objective of this study was to determine if the genes for the putative ammonia transporters, Rhesus glycoproteins (Rh) and the facilitated urea transporter (UT) were expressed during early development of rainbow trout, Oncorhynchus mykiss Walbaum. We predicted that the Rh isoforms Rhbg, Rhcg1 and Rhcg2 would be expressed shortly after fertilization but UT expression would be delayed based on the ontogenic pattern of nitrogen excretion. Embryos were collected 3, 14 and 21 days postfertilization (dpf), whereas yolk sac larvae were sampled at 31 dpf and juveniles at 60 dpf (complete yolk absorption). mRNA levels were quantified using quantitative polymerase chain reaction and expressed relative to the control gene, elongation factor 1alpha. All four genes (Rhbg, Rhcg1, Rhcg2, UT) were detected before hatching (25-30 dpf). As predicted, the mRNA levels of the Rh genes, especially Rhcg2, were relatively high early in embryonic development (14 and 21 dpf), but UT mRNA levels remained low until after hatching (31 and 60 dpf). These findings are consistent with the pattern of nitrogen excretion in early stages of trout development. We propose that early expression of Rh genes is critical for the elimination of potentially toxic ammonia from the encapsulated embryo, whereas retention of the comparatively benign urea molecule until after hatch is less problematic for developing tissues and organ systems.
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Affiliation(s)
- Carrie C Hung
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
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31
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Taylor DS, Turner BJ, Davis WP, Chapman BB. A novel terrestrial fish habitat inside emergent logs. Am Nat 2008; 171:263-6. [PMID: 18197778 DOI: 10.1086/524960] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Reports of new habitats for a major group of organisms are rare. Fishes display diverse adaptations for temporary (amphibious) existence on land, but to our knowledge, none have ever been reported regularly living inside emergent logs. Here, we show that the mangrove killifish, Kryptolebias marmoratus, a species previously known to emerse (leave the water) regularly, is now known to emerse and aggregate in large numbers inside decaying mangrove logs that have been "galleried" by terrestrial insects. This behavior has now been documented in both Belize, Central America, and Florida, U.S.A., populations and represents the first known case of fishes entering terrestrial woody material. The dense packing of fish in the narrow log galleries may imply a novel social context in which intraspecific aggressive behaviors are reduced, possibly mediated by the physiological limitations imposed within this restrictive habitat.
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Affiliation(s)
- D Scott Taylor
- Brevard County Environmentally Endangered Lands Program, 91 East Drive, Melbourne, Florida 32904, USA.
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32
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Ong KJ, Stevens ED, Wright PA. Gill morphology of the mangrove killifish (Kryptolebias marmoratus) is plastic and changes in response to terrestrial air exposure. ACTA ACUST UNITED AC 2007; 210:1109-15. [PMID: 17371909 DOI: 10.1242/jeb.002238] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Amphibious mangrove killifish, Kryptolebias marmoratus (formerly Rivulus marmoratus), are frequently exposed to aerial conditions in their natural environment. We tested the hypothesis that gill structure is plastic and that metabolic rate is maintained in response to air exposure. During air exposure, when gills are no longer functional, we predicted that gill surface area would decrease. In the first experiment, K. marmoratus were exposed to either water (control) or air for 1 h, 1 day, 1 week, or 1 week followed by a return to water for 1 week (recovery). Scanning electron micrographs (SEM) and light micrographs of gill sections were taken, and morphometric analyses of lamellar width, lamellar length and interlamellar cell mass (ILCM) height were performed. Following 1 week of air exposure, SEM indicated that there was a decrease in lamellar surface area. Morphometric analysis of light micrographs revealed that there were significant changes in the height of the ILCM, but there were no significant differences in lamellae width and length between any of the treatments. Following 1 week of recovery in water, the ILCM regressed and gill lamellae were similar to control fish, indicating that the morphological changes were reversible. In the second experiment, V(CO(2)) was measured in fish continuously over a 5-day period in air and compared with previous measurements of oxygen uptake (V(O(2))) in water. V(CO(2)) varied between 6 and 10 micromol g(-1) h(-1) and was significantly higher on days 3, 4 and 5 relative to days 1 and 2. In contrast to V(O(2)) in water, V(CO(2)) in air showed no diurnal rhythm over a 24 h period. These findings indicate that K. marmoratus remodel their gill structures in response to air exposure and that these changes are completely reversible. Furthermore, over a similar time frame, changes in V(CO(2)) indicate that metabolic rate is maintained at a rate comparable to that of fish in water, underlying the remarkable ability of K. marmoratus to thrive in both aquatic and terrestrial habitats.
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Affiliation(s)
- K J Ong
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada
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Tatarenkov A, Gao H, Mackiewicz M, Taylor DS, Turner BJ, Avise JC. Strong population structure despite evidence of recent migration in a selfing hermaphroditic vertebrate, the mangrove killifish (Kryptolebias marmoratus). Mol Ecol 2007; 16:2701-11. [PMID: 17594441 DOI: 10.1111/j.1365-294x.2007.03349.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We employ a battery of 33 polymorphic microsatellite loci to describe geographical population structure of the mangrove killifish (Kryptolebias marmoratus), the only vertebrate species known to have a mixed-mating system of selfing and outcrossing. Significant population genetic structure was detected at spatial scales ranging from tens to hundreds of kilometres in Florida, Belize, and the Bahamas. The wealth of genotypic information, coupled with the highly inbred nature of most killifish lineages due to predominant selfing, also permitted treatments of individual fish as units of analysis. Genetic clustering algorithms, neighbour-joining trees, factorial correspondence, and related methods all earmarked particular killifish specimens as products of recent outcross events that could often be provisionally linked to specific migration events. Although mutation is the ultimate source of genetic diversity in K. marmoratus, our data indicate that interlocality dispersal and outcross-mediated genetic recombination (and probably genetic drift also) play key proximate roles in the local 'clonal' dynamics of this species.
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Affiliation(s)
- Andrey Tatarenkov
- Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA.
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Nawata CM, Hung CCY, Tsui TKN, Wilson JM, Wright PA, Wood CM. Ammonia excretion in rainbow trout (Oncorhynchus mykiss): evidence for Rh glycoprotein and H+-ATPase involvement. Physiol Genomics 2007; 31:463-74. [PMID: 17712040 DOI: 10.1152/physiolgenomics.00061.2007] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Branchial ammonia transport in freshwater teleosts is not well understood. Most studies conclude that NH(3) diffuses out of the gill and becomes protonated to NH(4)(+) in an acidified gill boundary layer. Rhesus (Rh) proteins are new members of the ammonia transporter superfamily and rainbow trout possess genes encoding for Rh30-like1 and Rhcg2. We identified seven additional full-length trout Rh cDNA sequences: one Rhag and two each of Rhbg, Rhcg1, and Rh30-like. The mRNA expression of Rhbg, Rhcg1, and Rhcg2 was examined in trout tissues (blood, brain, eye, gill, heart, intestine, kidney, liver, muscle, skin, spleen) exposed to high external ammonia (HEA; 1.5 mmol/l NH(4)HCO(3), pH 7.95, 15 degrees C). Rhbg was expressed in all tissues, Rhcg1 was expressed in brain, gill, liver, and skin, and Rhcg2 was expressed in gill and skin. Brain Rhbg and Rhcg1 were downregulated, blood Rh30-like and Rhag were downregulated, and skin Rhbg and Rhcg2 were upregulated with HEA. After an initial uptake of ammonia into the fish during HEA, excretion was reestablished, coinciding with upregulations of gill Rh mRNA in the pavement cell fraction: Rhcg2 at 12 and 48 h, and Rhbg at 48 h. NHE2 expression remained unchanged, but upregulated H(+)-ATPase (V-type, B-subunit) and downregulated carbonic anhydrase (CA2) expression and activity were noted in the gill and again expression changes occurred in pavement cells, and not in mitochondria-rich cells. Together, these results indicate Rh glycoprotein involvement in ammonia transport and excretion in the rainbow trout while underscoring the significance of gill boundary layer acidification by H(+)-ATPase.
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Affiliation(s)
- C Michele Nawata
- Department of Biology, McMaster University, Hamilton, Ontario, Canada.
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Hung CYC, Tsui KNT, Wilson JM, Nawata CM, Wood CM, Wright PA. Rhesus glycoprotein gene expression in the mangrove killifish Kryptolebias marmoratus exposed to elevated environmental ammonia levels and air. J Exp Biol 2007; 210:2419-29. [PMID: 17601945 DOI: 10.1242/jeb.002568] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
SUMMARY
The mechanism(s) of ammonia excretion in the presence of elevated external ammonia are not well understood in fish. Recent studies in other organisms have revealed a new class of ammonia transporters, Rhesus glycoprotein genes(Rh genes), which may also play a role in ammonia excretion in fish. The first objective of this study was to clone and characterize Rhgenes in a fish species with a relatively high tolerance to environmental ammonia, the mangrove killifish Kryptolebias marmoratus (formerly Rivulus marmoratus). We obtained full-length cDNAs of three Rh genes in K. marmoratus: RhBG (1736 bp), RhCG1 (1920 bp) and RhCG2 (2021 bp), which are highly homologous with other known Rh gene sequences. Hydropathy analysis revealed that all three Rh genes encode membrane proteins with 10–12 predicted transmembrane domains. RhBG, RhCG1 and RhCG2 are highly expressed in gill tissue, with RhBG also present in skin of K. marmoratus. Exposure to elevated environmental ammonia (2 mmol l–1 NH4HCO3) for 5 days resulted in a modest (+37%) increase in whole-body ammonia levels, whereas gill RhCG2 and skin RhCG1 mRNA levels were upregulated by 5.8- and 7.7-fold, respectively. RhBG mRNA levels were also increased in various tissues, with 3- to 7-fold increases in the liver and skeletal muscle. In a separate group of killifish exposed to air for 24 h, RhCG1 and RhCG2 mRNA levels were elevated by 4- to 6-fold in the skin. Thus, the multifold induction of Rh mRNA levels in excretory tissues (gills and skin) and internal tissues in response to conditions that perturb normal ammonia excretion suggests that RhBG, RhCG1 and RhCG2 may be involved in facilitating ammonia transport in this species. Furthermore, the findings support earlier studies demonstrating that the skin is an important site of ammonia excretion in K. marmoratus.
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Affiliation(s)
- C Y C Hung
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada
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