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Huber ED, Hintz LL, Wilmoth B, McKenna JR, Hintz WD. Coping with stress: Salt type, concentration, and exposure history limit life history tradeoffs in response to road salt salinization. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 949:174998. [PMID: 39053528 DOI: 10.1016/j.scitotenv.2024.174998] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2024] [Revised: 06/22/2024] [Accepted: 07/22/2024] [Indexed: 07/27/2024]
Abstract
Substantial increases in the salinity of freshwater ecosystems has occurred around the globe from causes such as climate change, industrial operations, and the application of road deicing salts. We know very little about how plastic responses in life history traits or rapid evolution of new traits among freshwater organisms could promote stability in ecological communities affected by salinization. We performed a cohort life history analysis from birth to death with 180 individuals of a ubiquitous freshwater zooplankter to understand how life history traits are affected by exposure to two common salt types causing salinization-sodium chloride (NaCl) and calcium chloride (CaCl2)-across two environmentally relevant concentrations. We also tested if a multi-generational exposure history to high salinity altered life-history responses. We tracked and measured lifespan, time to maturation, brood size, brood interval, and body size. We found smaller brood sizes but slightly longer lifespans occurred at a low concentration of NaCl (230 mg Cl-/L). The longer lifespans led to more, albeit smaller broods, which generated a similar lifetime reproductive output compared to the no-salt control populations. At higher concentrations of NaCl and CaCl2, we found lifetime reproductive output was reduced by 23 % to 83 % relative to control populations because no tradeoff among life history traits occurred. In CaCl2, we observed shorter life spans, longer time intervals between smaller broods, and smaller body sizes leading to reduced lifetime reproductive output. We also found that a multi-generational exposure to the salt types did not convey any advantages for lifetime reproductive output. In some cases, the exposure history worsened the life history trait responses suggesting maladaptation. Our findings suggest that life history tradeoffs for freshwater species can occur in response to salinization, but these tradeoffs will largely depend on salt type and concentration, which will have implications for biodiversity and ecological stability.
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Affiliation(s)
- Eric D Huber
- Department of Environmental Sciences and Lake Erie Center, The University of Toledo, 6200 Bay Shore Rd., Oregon, OH, USA
| | - Leslie L Hintz
- Department of Environmental Sciences and Lake Erie Center, The University of Toledo, 6200 Bay Shore Rd., Oregon, OH, USA
| | - Bayley Wilmoth
- Department of Environmental Sciences and Lake Erie Center, The University of Toledo, 6200 Bay Shore Rd., Oregon, OH, USA
| | - Jorden R McKenna
- Department of Environmental Sciences and Lake Erie Center, The University of Toledo, 6200 Bay Shore Rd., Oregon, OH, USA
| | - William D Hintz
- Department of Environmental Sciences and Lake Erie Center, The University of Toledo, 6200 Bay Shore Rd., Oregon, OH, USA.
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Cochran JK, Orr SE, Funk DH, Figurskey AC, Reiskind MH, Buchwalter DB. Variation in Freshwater Insect Osmoregulatory Traits: A Comparative Approach. ECOLOGICAL AND EVOLUTIONARY PHYSIOLOGY 2024; 97:164-179. [PMID: 38875141 DOI: 10.1086/730689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2024]
Abstract
AbstractFreshwater salinity regimes vary naturally and are changing in response to anthropogenic activities. Few insect species tolerate saline waters, and biodiversity losses are associated with increasing salinity in freshwater. We used radiotracers (22Na, 35SO4, and 45Ca) to examine ion uptake rates across concentration gradients in mayflies (Ephemeroptera), caddis flies (Trichoptera), and mosquitoes (Diptera) and made observations for some traits in seven other taxa representing mayflies, stone flies (Plecoptera), true flies (Diptera), and true bugs (Hemiptera). We further assessed the permeability of the cuticle to 3H2O influx and 22Na efflux when faced with deionized water in these same taxa. We hypothesized a relationship between uptake rates and reported saline tolerances, but our data did not support this hypothesis, likely because acclimatory responses were not part of this experimental approach. However, we found several common physiological traits across the taxa studied, including (i) ionic uptake rates that were always positively correlated with dissolved concentrations, (ii) generally low Ca uptake rates relative to other freshwater taxa, (iii) greater Na loss than Na uptake in dilute conditions, (iv) ion uptake that was more variable in ion-rich conditions than in dilute conditions, and (v) 3H2O influx that occurs quickly (but this rapidly exchangeable pool of body water accounts for a surprisingly small percentage of the water content of species tested). There remains much to learn about the physiology of these important organisms in the face of changing salinity regimes worldwide.
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Cochran JK, Banks C, Buchwalter DB. Respirometry reveals major lineage-based differences in the energetics of osmoregulation in aquatic invertebrates. J Exp Biol 2023; 226:jeb246376. [PMID: 37767711 PMCID: PMC10629685 DOI: 10.1242/jeb.246376] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Accepted: 09/08/2023] [Indexed: 09/29/2023]
Abstract
All freshwater organisms are challenged to control their internal balance of water and ions in strongly hypotonic environments. We compared the influence of external salinity on the oxygen consumption rates (ṀO2) of three species of freshwater insects, one snail and two crustaceans. Consistent with available literature, we found a clear decrease in ṀO2 with increasing salinity in the snail Elimia sp. and crustaceans Hyalella azteca and Gammarus pulex (r5=-0.90, P=0.03). However, we show here for the first time that metabolic rate was unchanged by salinity in the aquatic insects, whereas ion transport rates were positively correlated with higher salinities. In contrast, when we examined the ionic influx rates in the freshwater snail and crustaceans, we found that Ca uptake rates were highest under the most dilute conditions, while Na uptake rates increased with salinity. In G. pulex exposed to a serially diluted ion matrix, Ca uptake rates were positively associated with ṀO2 (r5=-0.93, P=0.02). This positive association between Ca uptake rate and ṀO2 was also observed when conductivity was held constant but Ca concentration was manipulated (1.7-17.3 mg Ca l-1) (r5=0.94, P=0.05). This finding potentially implicates the cost of calcium uptake as a driver of increased metabolic rate under dilute conditions in organisms with calcified exoskeletons and suggests major phyletic differences in osmoregulatory physiology. Freshwater insects may be energetically challenged by higher salinities, while lower salinities may be more challenging for other freshwater taxa.
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Affiliation(s)
- Jamie K. Cochran
- Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695, USA
| | - Catelyn Banks
- North Carolina School of Science and Mathematics, 1219 Broad St, Durham, NC 27705, USA
| | - David B. Buchwalter
- Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695, USA
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4
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Orr SE, Collins LB, Jima DD, Buchwalter DB. Salinity-induced ionoregulatory changes in the gill proteome of the mayfly, Neocloeon triangulifer. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2023; 316:120609. [PMID: 36368556 DOI: 10.1016/j.envpol.2022.120609] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Revised: 10/06/2022] [Accepted: 11/04/2022] [Indexed: 06/16/2023]
Abstract
Ecologists have observed declines in the biodiversity of sensitive freshwater organisms in response to increasing concentrations of major ions (salinization). Yet, how changing salinities physiologically challenge aquatic organisms, such as mayflies, remains remarkably understudied. Moreover, it is not well understood the degree to which species respond and acclimate to salinity changes. Our lab is developing the Baetid mayfly, N. triangulifer, as a model organism for physiological research. We have previously described acclimatory changes in both ion flux rates and altered mRNA transcript levels in response to chronic exposures to elevated major ion concentrations at the whole animal level. In the present study, we use shotgun proteomics to identify the specific proteins associated with apical ion transport and how their abundance changes in response to chronic salinity exposures in gills. Gills were isolated from the penultimate nymphal stage of N. triangulifer reared under control culture conditions, elevated NaCl (157 mg L-1 Na), elevated CaCl2 (121 mg L-1 Ca), elevated Ca/MgSO4 (735 mg L-1 SO4). These conditions mirrored those from previously published physiological work. We also acutely exposed nymphs to dilute (50% dilution of culture water with deionized water) to explore proteomic changes in the gills in response to dilute conditions. We report 710 unique peptide sequences among treatment groups, including important apical ion transporters such as Ca-ATPase, Na/K ATPase, and V-ATPase. Treatment with elevated NaCl and Ca/MgSO4 appeared to cause more significant differential protein expression (452 and 345, respectively) compared to CaCl2 and dilute groups (134 and 17, respectively). Finally, we demonstrated the breadth of physiological functions in gills by exploring non-transport related pathways found in our dataset, including ATP synthesis, calcium signaling, and oxidative stress response. We discuss our results in the context of freshwater salinization and the challenges of working with non-model species without fully sequenced and annotated genomes.
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Affiliation(s)
- Sarah E Orr
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, 27695, USA
| | - Leonard B Collins
- Molecular Education, Technology and Research Innovation Center, North Carolina State University, Raleigh, NC, 27695, USA
| | - Dereje D Jima
- Center for Human Health and the Environment, North Carolina State University, Raleigh, NC, 27695, USA; Bioinformatics Research Center, North Carolina State University, Raleigh, NC, 27695, USA
| | - David B Buchwalter
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, 27695, USA.
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Fanelli RM, Cashman MJ, Porter AJ. Identifying Key Stressors Driving Biological Impairment in Freshwater Streams in the Chesapeake Bay Watershed, USA. ENVIRONMENTAL MANAGEMENT 2022; 70:926-949. [PMID: 36207606 PMCID: PMC9622507 DOI: 10.1007/s00267-022-01723-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Accepted: 09/15/2022] [Indexed: 06/16/2023]
Abstract
Biological communities in freshwater streams are often impaired by multiple stressors (e.g., flow or water quality) originating from anthropogenic activities such as urbanization, agriculture, or energy extraction. Restoration efforts in the Chesapeake Bay watershed, USA seek to improve biological conditions in 10% of freshwater tributaries and to protect the biological integrity of existing healthy watersheds. To achieve these goals, resource managers need to better understand which stressors are most likely driving biological impairment. Our study addressed this knowledge gap through two approaches: 1) reviewing and synthesizing published multi-stressor studies, and 2) examining 303(d) listed impairments linked to biological impairment as identified by jurisdiction regulatory agencies (the states within the watershed and the District of Columbia). Results identified geomorphology (i.e., physical habitat), salinity, and toxic contaminants as important for explaining variability in benthic community metrics in the literature review. Geomorphology (i.e., physical habitat and sediment), salinity, and nutrients were the most reported stressors in the jurisdictional impairment analysis. Salinity is likely a major stressor in urban and mining settings, whereas geomorphology was commonly reported in agricultural settings. Toxic contaminants, such as pesticides, were rarely measured; more research is needed to quantify the extent of their effects in the region. Flow alteration was also highlighted as an important urban stressor in the literature review but was rarely measured in the literature or reported by jurisdictions as a cause of impairment. These results can be used to prioritize stressor monitoring by managers, and to improve stressor identification methods for identifying causes of biological impairment.
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Affiliation(s)
- Rosemary M Fanelli
- U.S. Geological Survey, South Atlantic Water Science Center, Raleigh, NC, USA.
| | - Matthew J Cashman
- U.S. Geological Survey, Maryland-D.C.-Delaware Water Science Center, Baltimore, MD, USA
| | - Aaron J Porter
- U.S. Geological Survey, Virginia-West Virginia Water Science Center, Richmond, VA, USA
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Hills KA, Hyne RV, Kefford BJ. Bicarbonate alone does not totally explain the toxicity from major ions of coal bed derived waters to freshwater invertebrates. ECOTOXICOLOGY (LONDON, ENGLAND) 2022; 31:967-975. [PMID: 35701565 PMCID: PMC9300549 DOI: 10.1007/s10646-022-02552-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Accepted: 04/27/2022] [Indexed: 06/15/2023]
Abstract
Concentrations of major ions in coal mine discharge waters and unconventional hydrocarbon produced waters derived from coal bed methane (CBM) production, are potentially harmful to freshwater ecosystems. Bicarbonate is a major constituent of produced waters from CBM and coal mining. However, little is known about the relative toxicity of differing ionic proportions, especially bicarbonate, found in these CBM waters. As all freshwater invertebrates tested are more acutely sensitive to sodium bicarbonate (NaHCO3) than sodium chloride (NaCl) or synthetic sea water, we tested the hypotheses that toxicity of CBM waters are driven by bicarbonate concentration, and waters containing a higher proportion of bicarbonate are more toxic to freshwater invertebrates than those with less bicarbonate. We compared the acute (96 h) lethal toxicity to six freshwater invertebrate species of NaHCO3 and two synthetic CBM waters, with ionic proportions representative of water from CBM wells across New South Wales (NSW) and Queensland (Qld), in Australia. The ranking of LC50 values expressed as total salinity was consistent with the hypotheses. However, when toxicity was expressed as bicarbonate concentration, the hypothesis that the toxicity of coal bed waters would be explained by bicarbonate concentration was not well supported, and other ionic components were either ameliorating or exacerbating the NaHCO3 toxicity. Our findings showed NaHCO3 was more toxic than NaCl and that the NaHCO3 proportion of synthetic CBM waters drives toxicity, however other ions are altering the toxicity of bicarbonate.
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Affiliation(s)
- Kasey A Hills
- Centre for Applied Water Sciences, Institute for Applied Ecology, University of Canberra, Bruce, ACT, 2601, Australia
- New South Wales Environmental Protection Authority, Locked Bag 5022, Parramatta, NSW, 2124, Australia
| | - Ross V Hyne
- Department of Planning, Industry and Environment, Environment Protection Science, Lidcombe Laboratories, Lidcombe, NSW, 2141, Australia
| | - Ben J Kefford
- Centre for Applied Water Sciences, Institute for Applied Ecology, University of Canberra, Bruce, ACT, 2601, Australia.
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Cochran JK, Buchwalter DB. The acclimatory response of the mayfly Neocloeon triangulifer to dilute conditions is linked to the plasticity of sodium transport. Proc Biol Sci 2022; 289:20220529. [PMID: 35892216 PMCID: PMC9326274 DOI: 10.1098/rspb.2022.0529] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Relative to a growing body of knowledge about the negative consequences of freshwater salinization, little is known about how aquatic insects respond to progressively ion-poor conditions. Here, we examined life-history and physiological acclimation in Neocloeon triangulifer by rearing nymphs from 1-day post-egg hatch to adulthood across a gradient of decreasing Na concentrations (15, 8, 4, 2 and 1 mg l-1 Na). We found no significant changes in survival, growth, development time and whole-body Na content across these treatments. Radiotracer data revealed that nymphs acclimated to their dilute exposures by increasing their rates of Na uptake and were able to maintain a relatively narrow range of uptake rates (±s.e.m.) of 38.5 ± 4.2 µg Na g-1 h-1 across all treatments. By contrast, the Na uptake rates observed in naive nymphs were much more concentration dependent. This acclimatory response is partially explained by differences in ionocyte counts on the gills of nymphs reared under different salinities. Acclimated nymphs were surprisingly less retentive of their sodium composition when subjected to deionized water challenge. By contrasting our findings with a previous N. triangulifer salinity acclimation study, we show a physiological affinity for dilute conditions in this emerging mayfly model.
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Affiliation(s)
- Jamie K. Cochran
- Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695, USA
| | - David B. Buchwalter
- Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695, USA
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8
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Fair H, Lanno R, Smiley PC. Tolerance of glacial-melt stoneflies (Plecoptera) and morphological responses of chloride cells to stream salinity. CHEMOSPHERE 2022; 293:133655. [PMID: 35051519 DOI: 10.1016/j.chemosphere.2022.133655] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 01/13/2022] [Accepted: 01/14/2022] [Indexed: 06/14/2023]
Abstract
Aquatic insects within glacial-melt streams are adapted to low dissolved inorganic ion concentrations. Increases in ion concentrations in glacial-melt streams are predicted with increasing air temperatures, which may impact future aquatic insect survival in these streams. We hypothesized that stonefly (Plecoptera) naiads from glacial-melt streams acclimated to different conductivity would differ in survival, median lethal concentrations, and chloride cell responses to elevated conductivity above that expected in our study streams. We conducted field bioassays in remote glacial-melt streams in southwestern China in 2015 and exposed representative stonefly naiads (Chloroperlidae, Nemouridae, Taeniopterygidae) from stream sites differing in conductivity to experimental conductivity ranging from 11 to 20,486 μS/cm for up to 216 h. We examined survivorship, calculated 96-h median lethal concentrations, and measured chloride cell responses with scanning electron microscopy. Chloroperlidae survival after 120 and 216 h did not differ (P > 0.05) among conductivity treatments. The combined Nemouridae/Taeniopterygidae survival after 120 and 216 h was the least (P < 0.05) in conductivity treatments >16,349 μS/cm. Taeniopterygidae survival after 120 h was also the least (P < 0.05) in conductivity treatments >16,349 μS/cm. The 96-h median lethal concentrations did not differ (P > 0.05) between the combined Nemouridae/Taeniopterygidae group (2306 μS/cm) and Taeniopterigydae (2002 μS/cm) and were lower (P < 0.05) than the 96-h median lethal concentration for Chloroperlidae (8167 μS/cm). Chloroperlidae caviform cell number, density, and area decreased (P < 0.05) with increasing conductivity. Taeniopterygidae caviform cell count decreased (P < 0.05) with increasing conductivity, but cell density and area did not. Chloroperlidae and Taeniopterygidae coniform cell characteristics and Nemouridae bulbiform cell characteristics were not affected by conductivity. Our results suggest that Chloroperlidae, Nemouridae, and Taeniopterygidae from glacial-melt streams in China may be able to tolerate moderate increases in conductivity (i.e., 100 to 200 μS/cm).
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Affiliation(s)
- Heather Fair
- Environmental Science Graduate Program, Ohio State University, Columbus, OH, USA.
| | - Roman Lanno
- Environmental Science Graduate Program, Ohio State University, Columbus, OH, USA; Department of Evolution, Ecology, and Organismal Biology, Ohio State University, Columbus, OH, USA
| | - Peter C Smiley
- USDA Agricultural Research Service, Soil Drainage Research Unit, Columbus, OH, USA
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Zhao M, Wang CY, Sun L, He Z, Yang PL, Liao HJ, Feng Y. Edible Aquatic Insects: Diversities, Nutrition, and Safety. Foods 2021; 10:3033. [PMID: 34945584 PMCID: PMC8700862 DOI: 10.3390/foods10123033] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Revised: 11/26/2021] [Accepted: 12/02/2021] [Indexed: 01/22/2023] Open
Abstract
Edible insects have great potential to be human food; among them, aquatic insects have unique characteristics and deserve special attention. Before consuming these insects, the nutrition and food safety should always be considered. In this review, we summarized the species diversity, nutrition composition, and food safety of edible aquatic insects, and also compared their distinguished characteristics with those of terrestrial insects. Generally, in contrast with the role of plant feeders that most terrestrial edible insect species play, most aquatic edible insects are carnivorous animals. Besides the differences in physiology and metabolism, there are differences in fat, fatty acid, limiting/flavor amino acid, and mineral element contents between terrestrial and aquatic insects. Furthermore, heavy metal, pesticide residue, and uric acid composition, concerning food safety, are also discussed. Combined with the nutritional characteristics of aquatic insects, it is not recommended to eat the wild resources on a large scale. For the aquatic insects with large consumption, it is better to realize the standardized cultivation before they can be safely eaten.
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Affiliation(s)
- Min Zhao
- Key Laboratory of Breeding and Utilization of Resource Insects of National Forestry and Grassland Administration, Research Institute of Resource Insects, Chinese Academy of Forestry, Kunming 650224, China; (M.Z.); (C.-Y.W.); (L.S.); (Z.H.); (P.-L.Y.)
| | - Cheng-Ye Wang
- Key Laboratory of Breeding and Utilization of Resource Insects of National Forestry and Grassland Administration, Research Institute of Resource Insects, Chinese Academy of Forestry, Kunming 650224, China; (M.Z.); (C.-Y.W.); (L.S.); (Z.H.); (P.-L.Y.)
| | - Long Sun
- Key Laboratory of Breeding and Utilization of Resource Insects of National Forestry and Grassland Administration, Research Institute of Resource Insects, Chinese Academy of Forestry, Kunming 650224, China; (M.Z.); (C.-Y.W.); (L.S.); (Z.H.); (P.-L.Y.)
| | - Zhao He
- Key Laboratory of Breeding and Utilization of Resource Insects of National Forestry and Grassland Administration, Research Institute of Resource Insects, Chinese Academy of Forestry, Kunming 650224, China; (M.Z.); (C.-Y.W.); (L.S.); (Z.H.); (P.-L.Y.)
| | - Pan-Li Yang
- Key Laboratory of Breeding and Utilization of Resource Insects of National Forestry and Grassland Administration, Research Institute of Resource Insects, Chinese Academy of Forestry, Kunming 650224, China; (M.Z.); (C.-Y.W.); (L.S.); (Z.H.); (P.-L.Y.)
| | - Huai-Jian Liao
- Institute of Leisure Agriculture, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China
| | - Ying Feng
- Key Laboratory of Breeding and Utilization of Resource Insects of National Forestry and Grassland Administration, Research Institute of Resource Insects, Chinese Academy of Forestry, Kunming 650224, China; (M.Z.); (C.-Y.W.); (L.S.); (Z.H.); (P.-L.Y.)
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10
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Silver S, Donini A. Physiological responses of freshwater insects to salinity: molecular-, cellular- and organ-level studies. J Exp Biol 2021; 224:272480. [PMID: 34652452 DOI: 10.1242/jeb.222190] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Salinization of freshwater is occurring throughout the world, affecting freshwater biota that inhabit rivers, streams, ponds, marshes and lakes. There are many freshwater insects, and these animals are important for ecosystem health. These insects have evolved physiological mechanisms to maintain their internal salt and water balance based on a freshwater environment that has comparatively little salt. In these habitats, insects must counter the loss of salts and dilution of their internal body fluids by sequestering salts and excreting water. Most of these insects can tolerate salinization of their habitats to a certain level; however, when exposed to salinization they often exhibit markers of stress and impaired development. An understanding of the physiological mechanisms for controlling salt and water balance in freshwater insects, and how these are affected by salinization, is needed to predict the consequences of salinization for freshwater ecosystems. Recent research in this area has addressed the whole-organism response, but the purpose of this Review is to summarize the effects of salinization on the osmoregulatory physiology of freshwater insects at the molecular to organ level. Research of this type is limited, and pursuing such lines of inquiry will improve our understanding of the effects of salinization on freshwater insects and the ecosystems they inhabit.
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Affiliation(s)
- Sydney Silver
- Department of Biology, York University, Toronto, ON M3J 1P3, Canada
| | - Andrew Donini
- Department of Biology, York University, Toronto, ON M3J 1P3, Canada
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11
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Orr SE, Negrão Watanabe TT, Buchwalter DB. Physiological plasticity and acclimatory responses to salinity stress are ion-specific in the mayfly, Neocloeon triangulifer. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2021; 286:117221. [PMID: 33975217 DOI: 10.1016/j.envpol.2021.117221] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Revised: 04/09/2021] [Accepted: 04/20/2021] [Indexed: 06/12/2023]
Abstract
Freshwater salinization is a rapidly emerging ecological issue and is correlated with significant declines in aquatic biodiversity. It remains unclear how changing salinity regimes affect the physiology of sensitive aquatic insects. We used the parthenogenetic mayfly, Neocloeon triangulifer, to ask how ionic exposure history alters physiological processes and responses to subsequent major ion exposures. Using radiotracers (22Na, 35SO4, and 45Ca), we observed that mayflies chronically reared in elevated sodium or sulfate (157 mg L-1 Na or 667 mg L-1 SO4) had 2-fold (p < 0.0001) and 8-fold (p < 0.0001) lower ion uptake rates than mayflies reared in dilute control water (16 mg L-1 Na and 23 mg L-1 SO4) and subsequently transferred to elevated salinities, respectively. These acclimatory ion transport changes provided protection in 96-h toxicity bioassays for sodium, but not sulfate. Interestingly, calcium uptake was uniformly much lower and minimally influenced by exposure history, but was poorly tolerated in the toxicity bioassays. With qRT-PCR, we observed that the expression of many ion transporter genes in mayflies was influenced by elevated salinity in an ion-specific manner (general upregulation in response to sulfate, downregulation in response to calcium). Elevated sodium exposure had minimal influence on the same genes. Finally, we provide novel light microscopic evidence of histomorphological changes within the epithelium of the Malpighian tubules (insect primary excretory system) that undergoes cellular degeneration and necrosis secondary to calcium toxicity. We conclude that physiological plasticity to salinity stress is ion-specific and provide evidence for ion-specific toxicity mechanisms in N. triangulifer.
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Affiliation(s)
- Sarah E Orr
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, 27607, USA
| | - Tatiane Terumi Negrão Watanabe
- Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, 27607, USA
| | - David B Buchwalter
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, 27607, USA.
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12
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Assessing the Impacts of Chloride and Sulfate Ions on Macroinvertebrate Communities in Ohio Streams. WATER 2021. [DOI: 10.3390/w13131815] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Salinization of freshwaters is a growing concern, especially in urban catchments. Existing aquatic life criteria for chloride (230 mg/L; a US standard) or total dissolved solids (1500 mg/L; specific to Ohio) do not protect sensitive species, and standards for sulfate have yet to be promulgated on the national level. To help identify water quality thresholds for protection and restoration, species sensitivity distributions were compiled for chloride and sulfate based on field observations of macroinvertebrate communities co-located with water quality samples obtained from rivers and streams throughout Ohio. Additionally, attainment of biological benchmarks for macroinvertebrate communities found in headwater streams were modeled against chloride and sulfate using Bayesian logistic regression. The hazard concentration based on statewide data for chloride was 52 mg/L. The hazard concentration for sulfate based on data from the Western Allegheny Plateau ecoregion was 152 mg/L. The median effect levels from logistic regression for chloride and sulfate varied by ecoregion. Mayfly taxa were disproportionately represented in taxa comprising the lower 5th percentile of the species sensitivity distributions for chloride. However, logistic regression models of individual taxa response (as presence/absence) revealed that some taxa considered sensitive to pollution in general were highly tolerant of chloride. For 166 taxa showing directional response to chloride, 91 decreased and 75 increased. For the 97 individual taxa showing directional responses to sulfate, 81 decreased. Of the 16 taxa showing an increase, 6 are considered tolerant of pollution, 9 facultative and 1 moderately intolerant, the latter being taxa in the dipteran family Tipulidae. The hazard concentrations are useful as protective thresholds for existing high-quality waters. The logistic regression model of attainment can be used to inform management goals conditional on site-specific information.
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13
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Lambret P, Janssens L, Stoks R. The impact of salinity on a saline water insect: Contrasting survival and energy budget. JOURNAL OF INSECT PHYSIOLOGY 2021; 131:104224. [PMID: 33736984 DOI: 10.1016/j.jinsphys.2021.104224] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Revised: 02/09/2021] [Accepted: 03/09/2021] [Indexed: 06/12/2023]
Abstract
Water salinity is a major driver of aquatic insects' distribution. Saline species are usually generalists with high survival and performance at both low and high salinity levels. Yet, costs of high salinity may be underestimated as these are most often measured in terms of larval life history traits, while effects of larval stressors may only be detectable when looking at physiological traits and traits in the adult stage. Here, we assessed the lethal and sublethal physiological effects of embryonic and larval exposure to a range of salinity levels in the damselfly Lestes macrostigma, both during and after metamorphosis. This species inhabits temporary freshwaters where salinity increases during the drying phase. Salinity had no effect on egg hatching success within the range 2-9.5 g/L sea salt (conductivity range 3.45-14.52 mS/cm). With increasing salinity (up to 16 g/L, 23.35 mS/cm), growth rate decreased and larvae took longer to emerge and did so at a smaller size. Larval survival to metamorphosis increased with salinity up to 8 g/L (12.45 mS/cm) and then declined at 16 g/L. Exposure to salinity in the larval stage had no effect across metamorphosis on both the adult thorax muscle mass and flight performance, and the investment in immune function. Increasing salinity in the larval stage also had no effect on the energy available but increased the energy consumption in the adult stage, resulting in a lower net energy budget. These negative sublethal effects of increasing salinity hence bridged metamorphosis and contrasted with the mortality data, suggesting that the higher mortality at the low salinity levels selected for larvae with the best body condition. Our results highlight the importance of taking into account other life-history and physiological traits, besides mortality, ideally across different life stages, to better understand and predict consequences of increasing salinization on freshwater insects.
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Affiliation(s)
- Philippe Lambret
- Tour du Valat, Research Institute for the Conservation of Mediterranean Wetlands, Le Sambuc, 13200 Arles, France; Evolutionary Stress Ecology and Ecotoxicology, KU Leuven, Deberiotstraat 32, 3000 Leuven, Belgium.
| | - Lizanne Janssens
- Evolutionary Stress Ecology and Ecotoxicology, KU Leuven, Deberiotstraat 32, 3000 Leuven, Belgium
| | - Robby Stoks
- Evolutionary Stress Ecology and Ecotoxicology, KU Leuven, Deberiotstraat 32, 3000 Leuven, Belgium
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14
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Griffith MB, Lazorchak JM, Haring H. Uptake of Sulfate from Ambient Water by Freshwater Animals. WATER 2020; 12:1-1496. [PMID: 32704397 PMCID: PMC7376752 DOI: 10.3390/w12051496] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
To better understand how the sulfate (SO4 2-) anion may contribute to the adverse effects associated with elevated ionic strength or salinity in freshwaters, we measured the uptake and efflux of SO4 2- in four freshwater species: the fathead minnow (Pimephales promelas, Teleostei: Cyprinidae), paper pondshell (Utterbackia imbecillis, Bivalvia: Unionidae), red swamp crayfish (Procambarus clarkii, Crustacea: Cambaridae), and two-lined mayfly (Hexagenia bilineata, Insecta: Ephemeridae). Using δ( 34 S/ 32 S) stable isotope ratios and the concentrations of S and SO4 2-, we measured the SO4 2- influx rate (J in ), net flux (J net ), and efflux rate (Jout) during a 24 h exposure period. For all four species, the means of J in for SO4 2- were positive, and J in was significantly greater than 0 at both target SO4 2- concentrations in the fish and mollusk and at the lower SO4 2- concentration in the crayfish. The means of J out and J net were much more variable than those for J in , but several species by target SO4 2- concentration combinations for J out and J net , were negative, which suggests the net excretion of SO4 2- by the animals. The results of our experiments suggest a greater regulation of SO4 2- in freshwater animals than has been previously reported.
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Affiliation(s)
- Michael B. Griffith
- U.S. Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment, Cincinnati, OH 45268, USA
- U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Measurement and Modeling, Cincinnati, OH 45268, USA
| | - James M. Lazorchak
- U.S. Environmental Protection Agency, Office of Research and Development, Center for Environmental Measurement and Modeling, Cincinnati, OH 45268, USA
- U.S. Environmental Protection Agency, Office of Research and Development, National Exposure Research Laboratory, Cincinnati, OH 45268, USA
| | - Herman Haring
- Pegasus Technical Services, Inc., Cincinnati, OH 45268, USA
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15
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Orr SE, Buchwalter DB. It's all about the fluxes: Temperature influences ion transport and toxicity in aquatic insects. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2020; 221:105405. [PMID: 32014642 DOI: 10.1016/j.aquatox.2020.105405] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2019] [Revised: 12/30/2019] [Accepted: 01/04/2020] [Indexed: 06/10/2023]
Abstract
Many freshwater ecosystems are becoming saltier and/or warmer, but our understanding of how these factors interact and affect the physiology and life history outcomes of most aquatic species remain unknown. We hypothesize that temperature modulates ion transport rates. Since ion transport is energetically expensive, increases in salinity and/or temperature may influence ion flux rates and ultimately, organismal performance. Radiotracer (22Na+, 35SO4-2, and 45Ca2+) experiments with lab-reared mayflies (N. triangulifer) and other field-collected insects showed that increasing temperature generally increased ion transport rates. For example, increasing temperature from 15 °C to 25 °C, increased 22Na+ uptake rates by two-fold (p < 0.0001) and 35SO4-2 uptake rates by four-fold (p < 0.0001) in the caddisfly, Hydropsyche sparna. Smaller changes in 22Na+ and 35SO4-2 uptake rates were observed in the mayflies, Isonychia sayi and Maccaffertium sp., suggesting species-specific differences in the thermal sensitivity of ion transport. Finally, we demonstrated that the toxicity of SO4 was influenced by temperature profoundly in a 96-h bioassay. Under the saltiest conditions (1500 mg L-1 SO4), mayfly survival was 78 % at 15 °C, but only 44 % at 25 °C (p < 0.0036). Conceivably, the energetic cost of osmoregulation in warmer, saltier environments may cause significant major ion toxicity in certain freshwater insects.
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Affiliation(s)
- Sarah E Orr
- North Carolina State University, United States
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16
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Ciparis S, Rhyne G, Stephenson T. Exposure to Elevated Concentrations of Major Ions Decreases Condition Index of Freshwater Mussels: Comparison of Metrics. ACTA ACUST UNITED AC 2019. [DOI: 10.31931/fmbc.v22i2.2019.98-108] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Serena Ciparis
- U.S. Fish and Wildlife Service, Virginia Field Office, Gloucester, VA 23061 USA
| | - Garrett Rhyne
- Department of Fish and Wildlife Conservation, Virginia Tech, Blacksburg, VA 24061 USA
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17
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Mangahas RS, Murray RL, McCauley SJ. Chronic Exposure to High Concentrations of Road Salt Decreases the Immune Response of Dragonfly Larvae. Front Ecol Evol 2019. [DOI: 10.3389/fevo.2019.00376] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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18
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Bracewell S, Verdonschot RCM, Schäfer RB, Bush A, Lapen DR, Van den Brink PJ. Qualifying the effects of single and multiple stressors on the food web structure of Dutch drainage ditches using a literature review and conceptual models. THE SCIENCE OF THE TOTAL ENVIRONMENT 2019; 684:727-740. [PMID: 30981441 DOI: 10.1016/j.scitotenv.2019.03.497] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Revised: 03/31/2019] [Accepted: 03/31/2019] [Indexed: 05/12/2023]
Abstract
In September 2017, a workshop was held at Wageningen University and Research to determine the current state of knowledge of multiple stressor effects on aquatic ecosystems and to assess how to improve prediction of these effects. We developed a theoretical framework that integrates species-level responses to stressors to predict how these effects propagate through higher levels of biological organisation. Here, we present the application of the framework for drainage ditch ecosystems in the Netherlands. We used food webs to assess single and multiple stressor effects of common stressors on ditch communities. We reviewed the literature for the effects of targeted stressors (nutrients, pesticides, dredging and mowing, salinization, and siltation) on each functional group present in the food web and qualitatively assessed the relative sensitivity of groups. Using this information, we created a stressor-response matrix of positive and negative direct effects of each stressor-functional group combination. Fungicides, salinization, and sedimentation were identified as particularly detrimental to most groups, although destructive management practices, such as dredging with almost complete community removal, would take precedence depending on frequency. Using the stressor-response matrix we built, first, a series of conceptual null models of single stressor effects on food web structure and, second, a series of additive null models to illustrate potential paired-stressor effects. We compared these additive null models with published studies of the same pairs of combined single stressors to explore more complex interactions. Our approach serves as a first-step to considering multiple stressor scenarios in systems that are understudied or data-poor and as a baseline from which more complex models that include indirect effects and quantitative data may be developed. We make specific suggestions for appropriate management strategies that could be taken to support the biodiversity of these systems for individual stressors and their combined impacts.
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Affiliation(s)
- Sally Bracewell
- Department of Aquatic Ecology and Water Quality Management, Wageningen University and Research, P.O. Box 47, 6700 AA Wageningen, the Netherlands.
| | - Ralf C M Verdonschot
- Wageningen Environmental Research, Wageningen University and Research, PO Box 47, 6700 AA, Wageningen, the Netherlands
| | - Ralf B Schäfer
- Institute for Environmental Sciences, University of Koblenz-Landau, Fortstrasse 7, 76829 Landau, Germany
| | - Alex Bush
- Environment Canada, Canadian Rivers Institute, Department of Biology, University of New Brunswick, PO Box 4400, Fredericton, New Brunswick E3B 5A3, Canada
| | - David R Lapen
- Ottawa Research and Development Centre, Agriculture and Agri-Food Canada, 960 Carling Ave., Ottawa, Ontario, K1A 0C6, Canada
| | - Paul J Van den Brink
- Department of Aquatic Ecology and Water Quality Management, Wageningen University and Research, P.O. Box 47, 6700 AA Wageningen, the Netherlands; Wageningen Environmental Research, Wageningen University and Research, PO Box 47, 6700 AA, Wageningen, the Netherlands
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Jackson JK, Funk DH. Temperature affects acute mayfly responses to elevated salinity: implications for toxicity of road de-icing salts. Philos Trans R Soc Lond B Biol Sci 2018; 374:rstb.2018.0081. [PMID: 30509923 DOI: 10.1098/rstb.2018.0081] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/23/2018] [Indexed: 11/12/2022] Open
Abstract
Salinity in freshwater ecosystems has increased significantly at numerous locations throughout the world, and this increase often reflects the use or production of salts from road de-icing, mining/oil and gas drilling activities, or agricultural production. When related to de-icing salts, highest salinity often occurs in winter when water temperature is often low relative to mean annual temperature at a site. Our study examined acute (96 h) responses to elevated salinity (NaCl) concentrations at five to seven temperature treatments (5-25°C) for four mayfly species (Baetidae: Neocloeon triangulifer, Procloeon fragile; Heptageniidae: Maccaffertium modestum; Leptophlebiidae: Leptophlebia cupida) that are widely distributed across eastern North America. Based on acute LC50s at 20°C, P. fragile was most sensitive (LC50 = 767 mg l-1, 1447 µS cm-1), followed by N. triangulifer (2755 mg l-1, 5104 µS cm-1), M. modestum (2760 mg l-1, 5118 µS cm-1) and L. cupida (4588 mg l-1, 8485 µS cm-1). Acute LC50s decreased as temperature increased for all four species (n = 5-7, R 2 = 0.65-0.88, p = 0.052-0.002). Thus, acute salt toxicity is strongly temperature dependent for the mayfly species we tested, which suggests that brief periods of elevated salinity during cold seasons or in colder locations may be ecologically less toxic than predicted by standard 20 or 25°C laboratory bioassays.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.
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Affiliation(s)
- John K Jackson
- Stroud Water Research Center, 970 Spencer Road, Avondale, PA 19311, USA
| | - David H Funk
- Stroud Water Research Center, 970 Spencer Road, Avondale, PA 19311, USA
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20
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Cañedo-Argüelles M, Kefford B, Schäfer R. Salt in freshwaters: causes, effects and prospects - introduction to the theme issue. Philos Trans R Soc Lond B Biol Sci 2018; 374:rstb.2018.0002. [PMID: 30509904 DOI: 10.1098/rstb.2018.0002] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/25/2018] [Indexed: 01/07/2023] Open
Abstract
Humans are globally increasing the salt concentration of freshwaters (i.e. freshwater salinization), leading to significant effects at the population, community and ecosystem level. The present theme issue focuses on priority research questions and delivers results that contribute to shaping the future research agenda on freshwater salinization as well as fostering our capacity to manage salinization. The issue is structured along five topics: (i) the estimation of future salinity and evaluation of the relative contribution of the different drivers; (ii) the physiological responses of organisms to alterations in ion concentrations with a specific focus on the osmophysiology of freshwater insects and the responses of different organisims to seawater intrusion; (iii) the impact of salinization on ecosystem functioning, also considering the connections between riparian and stream ecosystems; (iv) the role of context in moderating the response to salinization. The contributions scrutinise the role of additional stressors, biotic interactions, the identify of the ions and their ratios, as well as of the biogeographic and evolutionary context; and (v) the public discourse on salinization and recommendations for management and regulation. In this paper we introduce the general background of salinization, outline research gaps and report key findings from the contributions to this theme issue.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.
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Affiliation(s)
- Miguel Cañedo-Argüelles
- Grup de recerca FEHM (Freshwater Ecology, Hydrology and Management), Departament de Biologia Evolutiva, Ecologia i Ciència Ambientals, Universitat de Barcelona, Avda Diagonal 643, 08028 Barcelona, Spain
| | - Ben Kefford
- Institute for Applied Ecology, University of Canberra, Australian Capital Territory 2601, Australia
| | - Ralf Schäfer
- Department of Quantitative Landscape Ecology, University Koblenz-Landau, Fortstr. 7, 76829 Landau, Germany
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21
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Buchwalter D, Scheibener S, Chou H, Soucek D, Elphick J. Are sulfate effects in the mayfly Neocloeon triangulifer driven by the cost of ion regulation? Philos Trans R Soc Lond B Biol Sci 2018; 374:rstb.2018.0013. [PMID: 30509915 DOI: 10.1098/rstb.2018.0013] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/22/2018] [Indexed: 01/27/2023] Open
Abstract
Elevated major ion concentrations in streams are commonly observed as a consequence of resource extraction, de-icing and other anthropogenic activities. Ecologists report biodiversity losses associated with increasing salinity, with mayflies typically being highly responsive to increases of different major ions. In this study, we evaluated the performance of the mayfly Neocloeon triangulifer reared for its entire larval phase in a gradient of sulfate concentrations. Two natural waters were amended with SO4 as a blend of CaSO4 and MgSO4 and exposures ranged from 5 to 1500 mg l-1 SO4. Survival (per cent successful emergence to the subimago stage) was significantly reduced at the highest SO4 concentration in both waters, while development was significantly delayed at 667 mg l-1 SO4 Final sub-adult body weights were consistent across treatments, except at the highest treatment concentration. Despite evidence for sulfate uptake rates increasing with exposure concentrations and not being saturated at even extremely high SO4 concentrations, total body sulfur changed little in subimagos. Together, these results suggest that elevated SO4 imposes an energetic demand associated with maintaining homeostasis that is manifested primarily as reduced growth rates and associated developmental delays. We identified two genes related to sulfate transport in N. trianguliferThis article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.
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Affiliation(s)
- David Buchwalter
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, USA
| | - Shane Scheibener
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, USA
| | - Hsuan Chou
- Department of Biological Sciences, North Carolina State University, Raleigh, NC, USA
| | - David Soucek
- Illinois Natural History Survey, Champaign, IL, USA
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22
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Kefford BJ. Why are mayflies (Ephemeroptera) lost following small increases in salinity? Three conceptual osmophysiological hypotheses. Philos Trans R Soc Lond B Biol Sci 2018; 374:rstb.2018.0021. [PMID: 30509920 DOI: 10.1098/rstb.2018.0021] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/25/2018] [Indexed: 11/12/2022] Open
Abstract
The salinity of many freshwaters is increasing globally as a result of human activities. Associated with this increase in salinity are losses of Ephemeroptera (mayfly) abundance and richness. The salinity concentrations at which Ephemeroptera decline in nature are lower than their internal salinity or haemolymph osmolality. Many species also suffer substantial mortality in single species laboratory toxicity tests at salinities lower than their internal salinity. These findings are problematic as conventional osmoregulation theory suggests that freshwater animals should not experience stress where external osmolality is greater than haemolymph osmolality. Here I explore three hypotheses to explain salt sensitivity in Ephemeroptera. These conceptual hypotheses are based on the observations that as the external sodium ion (Na+) concentration increases so does the Na+ turnover rate (both uptake and elimination rates increase). Sulphate ([Formula: see text]) uptake in mayflies also increases with increasing external [Formula: see text] although, unlike Na+, its rate of increase decreases with increasing external [Formula: see text] The first hypothesis is premised on ion turnover being energetically costly. The first hypothesis proposes that individuals must devote a greater proportion of their energy to ion homeostasis at the expense of other uses including growth and development. Lethal levels of salinity presumably result from individuals not being able to devote enough energy to maintain ion homeostasis without critical loss of other vital functions. The second hypothesis is premised on the uptake of Na+ exchanged for (an outgoing) H+, leading to (localized) loss of pH regulation. The third hypothesis is premised on localized Na+ toxicity or poisoning with increased Na turnover as salinity increases. None of the proposed hypotheses is without potential problems, yet all are testable, and research effort should be focused at attempting to falsify them.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.
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Affiliation(s)
- Ben J Kefford
- Institute for Applied Ecology, University of Canberra, Canberra, Australian Capital Territory 2601, Australia
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Glover CN. Defence mechanisms: the role of physiology in current and future environmental protection paradigms. CONSERVATION PHYSIOLOGY 2018; 6:coy012. [PMID: 29564135 PMCID: PMC5848810 DOI: 10.1093/conphys/coy012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2017] [Revised: 02/09/2018] [Accepted: 02/22/2018] [Indexed: 05/13/2023]
Abstract
Ecological risk assessments principally rely on simplified metrics of organismal sensitivity that do not consider mechanism or biological traits. As such, they are unable to adequately extrapolate from standard laboratory tests to real-world settings, and largely fail to account for the diversity of organisms and environmental variables that occur in natural environments. However, an understanding of how stressors influence organism health can compensate for these limitations. Mechanistic knowledge can be used to account for species differences in basal biological function and variability in environmental factors, including spatial and temporal changes in the chemical, physical and biological milieu. Consequently, physiological understanding of biological function, and how this is altered by stressor exposure, can facilitate proactive, predictive risk assessment. In this perspective article, existing frameworks that utilize physiological knowledge (e.g. biotic ligand models, adverse outcomes pathways and mechanistic effect models), are outlined, and specific examples of how mechanistic understanding has been used to predict risk are highlighted. Future research approaches and data needs for extending the incorporation of physiological information into ecological risk assessments are discussed. Although the review focuses on chemical toxicants in aquatic systems, physical and biological stressors and terrestrial environments are also briefly considered.
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Affiliation(s)
- Chris N Glover
- Faculty of Science and Technology and Athabasca River Basin Research Institute, Athabasca University, Canada
- Department of Biological Sciences, CW 405, Biological Sciences Bldg. University of Alberta Edmonton, Alberta, Canada T6G 2E9
- Corresponding author: 1 University Drive, Athabasca, Alberta, Canada T9S 3A3. Tel: +(587) 985 8007.
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