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Holmstrup M, Sørensen JG, Dai W, Krogh PH, Schmelz RM, Slotsbo S. Analysis of heat and cold tolerance of a freeze-tolerant soil invertebrate distributed from temperate to Arctic regions: evidence of selection for extreme cold tolerance. J Comp Physiol B 2022; 192:435-445. [PMID: 35312816 DOI: 10.1007/s00360-022-01433-w] [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: 10/14/2021] [Revised: 03/01/2022] [Accepted: 03/07/2022] [Indexed: 10/18/2022]
Abstract
Tolerance to thermal extremes is critical for the geographic distributions of ectotherm species, many of which are probably going to be modified by future climatic changes. To predict species distributions it is important to understand the potential of species to adapt to changing thermal conditions. Here, we tested whether the thermal tolerance traits of a common freeze-tolerant potworm were correlated with climatic conditions and if adaptation to extreme cold constrains the evolutionary potential for high temperature tolerance. Further, we tested if evolution of thermal tolerance traits is associated with costs in other fitness traits (body size and reproduction). Lastly, we tested if slopes of temperature-survival curves (i.e., the sensitivity distribution) are related to tolerance itself. Using 24 populations of the potworm, Enchytraeus albidus Henle (Enchytraeidae), collected from a wide range of climatic conditions, we established a common garden experiment in which we determined high and low temperature tolerance (using survival as endpoint), average reproductive output and adult body size. Heat tolerance was not related to environmental temperatures whereas lower lethal temperature was about 10 °C lower in Arctic populations than in populations from temperate regions. Reproduction was not related to environmental temperature, but was negatively correlated with cold tolerance. One explanation for the trade-off between cold tolerance and reproduction could be that the more cold-hardy populations need to channel energy to large glycogen reserves at the expense of less energy expenditure for reproduction. Adult body size was negatively related to environmental temperature. Finally, the slopes of temperature-survival curves were significantly correlated with critical temperature limits for heat and cold tolerance; i.e., slopes increased with thermal tolerance. Our results suggest that relatively heat-sensitive populations possess genetic variation, leaving room for improved heat tolerance through evolutionary processes, which may alleviate the effects of a warmer future climate in the Arctic. On the other hand, we observed relatively narrow sensitivity distributions (i.e., less variation) in the most heat tolerant populations. Taken together, our results suggest that both cold and heat tolerance can only be selected for (and improved) until a certain limit has been reached.
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Affiliation(s)
- Martin Holmstrup
- Department of Ecoscience, Section of Terrestrial Ecology, Aarhus University, Vejlsøvej 25, 8600, Silkeborg, Denmark.
| | - Jesper G Sørensen
- Department of Biology, Section of Genetics, Ecology and Evolution, Aarhus University, Ny Munkegade 116, Building 1540, 8000, Aarhus C, Denmark
| | - Wencai Dai
- Department of Ecoscience, Section of Terrestrial Ecology, Aarhus University, Vejlsøvej 25, 8600, Silkeborg, Denmark
| | - Paul Henning Krogh
- Department of Ecoscience, Section of Terrestrial Ecology, Aarhus University, Vejlsøvej 25, 8600, Silkeborg, Denmark
| | - Rüdiger M Schmelz
- IFAB, Institute for Applied Soil Biology, Tomberg 24a, 22337, Hamburg, Germany
| | - Stine Slotsbo
- Department of Ecoscience, Section of Terrestrial Ecology, Aarhus University, Vejlsøvej 25, 8600, Silkeborg, Denmark
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Dai W, Slotsbo S, Holmstrup M. Thermal optimum for mass production of the live feed organism Enchytraeus albidus. J Therm Biol 2021; 97:102865. [PMID: 33863429 DOI: 10.1016/j.jtherbio.2021.102865] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Revised: 01/12/2021] [Accepted: 01/24/2021] [Indexed: 11/27/2022]
Abstract
Live feed organisms are essential for the larval stages of many fish species grown in aquaculture, and juvenile fish reared on live feeds often exhibit higher survival and growth than those reared on formulated feed. The terrestrial enchytraeid (white worm), Enchytraeus albidus, has potential as a sustainable source of live feed because it can easily be mass produced, feeds on a wide range of organic waste materials and has high contents of protein and long-chain poly-unsaturated fatty acids. In the present study, we observed the effect of temperature on population growth over five months using soil microcosms. At the outset, each microcosm was supplied with approximately the same number of cocoons. Hatched enchytraeids were given rolled oats ad libitum as feed. We followed the population growth at seven temperatures in the range of 4-25 °C and investigated body composition in order to find optimal temperature for mass production. Results showed that E. albidus has a broad thermal optimum range and displays almost similar biomass production in the range of 15-22 °C with specific growth rates between 6.5 and 6.8%. In this temperature range, protein contents were 40-45%, glycogen contents 20-25% and total fatty acid contents 15-20% of dry weight. The temperature had a highly significant effect on fatty acid composition. In particular, the abundance of omega-3 fatty acids (18:3ω3 and 20:5ω3) was largest at low temperature. For what concerns achievable density of worms in mass cultures, our results surpassed previous results and showed that densities close to 100 g L-1 substrate are realistic. Maximum production of biomass can likely reach 80 g live worms L-1 month-1 at temperatures between 15 and 22 °C.
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Affiliation(s)
- Wencai Dai
- Section for Terrestrial Ecology, Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600, Silkeborg, Denmark
| | - Stine Slotsbo
- Section for Terrestrial Ecology, Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600, Silkeborg, Denmark
| | - Martin Holmstrup
- Section for Terrestrial Ecology, Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600, Silkeborg, Denmark; Aarhus University Centre for Circular Bioeconomy, Department of Agroecology, Blichers Allé 20, DK-8830, Tjele, Denmark.
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Žagar A, Holmstrup M, Simčič T, Debeljak B, Slotsbo S. Comparing Enchytraeus albidus populations from contrasting climatic environments suggest a link between cold tolerance and metabolic activity. Comp Biochem Physiol A Mol Integr Physiol 2018; 224:35-41. [DOI: 10.1016/j.cbpa.2018.05.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2018] [Revised: 05/24/2018] [Accepted: 05/24/2018] [Indexed: 10/14/2022]
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de Boer TE, Roelofs D, Vooijs R, Holmstrup M, Amorim MJB. Population-specific transcriptional differences associated with freeze tolerance in a terrestrial worm. Ecol Evol 2018; 8:3774-3786. [PMID: 29686857 PMCID: PMC5901168 DOI: 10.1002/ece3.3602] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Revised: 10/13/2017] [Accepted: 10/13/2017] [Indexed: 12/25/2022] Open
Abstract
Enchytraeus albidus is a terrestrial earthworm widespread along the coasts of northern Europe and the Arctic. This species tolerates freezing of body fluids and survives winters in a frozen state. Their acclimatory physiological mechanisms behind freeze tolerance involve increased fluidity of membrane lipids during cold exposure and accumulation of cryoprotectants (glucose) during the freezing process. Gene regulatory processes of these physiological responses have not been studied, partly because no gene expression tools were developed. The main aim of this study was to understand whether the freeze tolerance mechanisms have a transcriptomic basis in E. albidus. For that purpose, first the transcriptome of E. albidus was assembled with RNAseq data. Second, two strains from contrasting thermal environments (Germany and Greenland) were compared by mapping barcoded RNAseq data onto the assembled transcriptome. Both of these strains are freeze tolerant, but Greenland is extremely freeze tolerant. Results showed more plastic responses in the Greenland strain as well as higher constitutive expression of particular stress response genes. These altered transcriptional networks are associated with an adapted homeostasis coping with prolonged freezing conditions in Greenland animals. Previously identified physiological alterations in freeze‐tolerant strains of E. albidus are underpinned at the transcriptome level. These processes involve anion transport in the hemolymph, fatty acid metabolism, metabolism, and transport of cryoprotective sugars as well as protection against oxidative stress. Pathway analysis supported most of these processes, and identified additional differentially expressed pathways such as peroxisome and Toll‐like receptor signaling. We propose that the freeze‐tolerant phenotype is the consequence of genetic adaptation to cold stress and may have driven evolutionary divergence of the two strains.
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Affiliation(s)
| | - Dick Roelofs
- Department of Ecological Science Faculty of Earth and Life Sciences VU University, Amsterdam Amsterdam The Netherlands
| | - Riet Vooijs
- Department of Ecological Science Faculty of Earth and Life Sciences VU University, Amsterdam Amsterdam The Netherlands
| | | | - Mónica J B Amorim
- Department of Biology and CESAM (Centre for Environmental and Marine Studies) University of Aveiro Aveiro Portugal
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Czechowski P, White D, Clarke L, McKay A, Cooper A, Stevens MI. Age-related environmental gradients influence invertebrate distribution in the Prince Charles Mountains, East Antarctica. ROYAL SOCIETY OPEN SCIENCE 2016; 3:160296. [PMID: 28083092 PMCID: PMC5210674 DOI: 10.1098/rsos.160296] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2016] [Accepted: 11/17/2016] [Indexed: 05/22/2023]
Abstract
The potential impact of environmental change on terrestrial Antarctic ecosystems can be explored by inspecting biodiversity patterns across large-scale gradients. Unfortunately, morphology-based surveys of Antarctic invertebrates are time-consuming and limited by the cryptic nature of many taxa. We used biodiversity information derived from high-throughput sequencing (HTS) to elucidate the relationship between soil properties and invertebrate biodiversity in the Prince Charles Mountains, East Antarctica. Across 136 analysed soil samples collected from Mount Menzies, Mawson Escarpment and Lake Terrasovoje, we found invertebrate distribution in the Prince Charles Mountains significantly influenced by soil salinity and/or sulfur content. Phyla Tardigrada and Arachnida occurred predominantly in low-salinity substrates with abundant nutrients, whereas Bdelloidea (Rotifera) and Chromadorea (Nematoda) were more common in highly saline substrates. A significant correlation between invertebrate occurrence, soil salinity and time since deglaciation indicates that terrain age indirectly influences Antarctic terrestrial biodiversity, with more recently deglaciated areas supporting greater diversity. Our study demonstrates the value of HTS metabarcoding to investigate environmental constraints on inconspicuous soil biodiversity across large spatial scales.
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Affiliation(s)
- Paul Czechowski
- Australian Centre for Ancient DNA, University of Adelaide, Adelaide, South Australia 5005, Australia
- Antarctic Biological Research Initiative, Bolivar, South Australia 5110, Australia
- Author for correspondence: Paul Czechowski e-mail:
| | - Duanne White
- Institute for Applied Ecology, University of Canberra, Canberra, Australian Capital Territory 2601, Australia
| | - Laurence Clarke
- Australian Centre for Ancient DNA, University of Adelaide, Adelaide, South Australia 5005, Australia
- Australian Antarctic Division, Kingston, Tasmania 7050, Australia
- Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tasmania 7001, Australia
| | - Alan McKay
- Plant and Soil Health, South Australian Research and Development Institute, Waite Campus, Urrbrae, South Australia 5064, Australia
| | - Alan Cooper
- Australian Centre for Ancient DNA, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Mark I. Stevens
- South Australian Museum, Science Centre, Adelaide, South Australia 5000, Australia
- School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, South Australia 5001, Australia
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Patrício-Silva AL, Amorim MJB. Effect of freeze-thaw cycles and 4-nonylphenol on cellular energy allocation in the freeze-tolerant enchytraeid Enchytraeus albidus. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2016; 23:3548-3555. [PMID: 26490934 DOI: 10.1007/s11356-015-5593-1] [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: 05/20/2015] [Accepted: 10/08/2015] [Indexed: 06/05/2023]
Abstract
Due to climate change and intense anthropogenic activity, organisms from cold regions are often exposed to combined effects of temperature fluctuations and contaminants. In this investigation, we assessed the lipid, protein, and carbohydrate energy budgets; the energy available (Ea); consumed (Ec); and cellular energy allocation (CEA) of the freeze-tolerant Enchytraeus albidus, when exposed to sublethal concentrations of 4-nonylphenol (a lipophilic contaminant) for 7 days, followed by exposure to different temperature regimes (continuous 2 °C, continuous -4 °C, and daily freeze-thaw cycles (FTC) (2 to -4 °C) for additional 10 days. Results showed that a pre-exposure to 4-nonylphenol (4-NP) induced important changes in the worms' energy budgets and CEA and increased mortality with most severe effects observed for the FTC events. For FTC, lipids were the most accumulated energy source, whereas during freezing (-4 °C), proteins were the most used. FTC caused the highest Ec, indicating the higher energy requirements for organisms when shifting between freezing and thawing events. This is also in line with the higher mortality observed in FTC compared to continuous -4 °C or 2 °C. Worms exposed to continuous freezing presented relatively stable and positive levels of Ea and low levels of Ec, possibly related with the decrease in metabolism.
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Affiliation(s)
- Ana L Patrício-Silva
- Department of Biology & CESAM (Centre for Environmental and Marine Studies), University of Aveiro, 3810-193, Aveiro, Portugal
| | - Mónica J B Amorim
- Department of Biology & CESAM (Centre for Environmental and Marine Studies), University of Aveiro, 3810-193, Aveiro, Portugal.
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Silva ALP, Amorim MJB, Holmstrup M. Salinity changes impact of hazardous chemicals in Enchytraeus albidus. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2015; 34:2159-2166. [PMID: 25943329 DOI: 10.1002/etc.3058] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2014] [Revised: 12/19/2014] [Accepted: 04/27/2015] [Indexed: 06/04/2023]
Abstract
Supralittoral ecosystems are among the most challenging environments for soil organisms, particularly when salinity fluctuations are involved, frequently combined with the presence of contaminants as a result of intense anthropogenic activities. Knowledge of how salinity influences the effect of contaminants in supralittoral species is crucial for determining the safety factors required when extrapolating results from optimal laboratory conditions to these natural ecosystems. The present study therefore evaluated the effects of 2 metals (copper and cadmium) and 2 organic compounds (carbendazim and 4-nonylphenol) in the absence or presence of 15‰ NaCl in the potworm Enchytraeus albidus, a model organism for ecotoxicology studies commonly found in supralittoral ecosystems, The potworms had a higher reproduction in saline soil than in control soil. Moreover, the effects of copper and carbendazim on reproduction were smaller than when they were tested in nonsaline soil. Potworms exposed to nonsaline soils also had significantly higher tissue concentrations of metals, which partly explains the effects on reproduction. The influence of salinity on effects of 4-nonylphenol was, however, less clear; effects on survival decreased in saline soil, but effects on reproduction were highest in saline soil. The latter slightly correlated with tissue concentrations of the chemical. The present study provides the first evidence that soil salinity has a significant influence on the impact of contaminants evaluated with the enchytraeid reproduction test.
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Affiliation(s)
- Ana L Patrício Silva
- Department of Biology and Center for Environmental and Marine Studies, University of Aveiro, Aveiro, Portugal
| | - Mónica J B Amorim
- Department of Biology and Center for Environmental and Marine Studies, University of Aveiro, Aveiro, Portugal
| | - Martin Holmstrup
- Department of Bioscience, Aarhus University, Silkeborg, Denmark
- Arctic Research Center, Aarhus University, Aarhus, Denmark
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Pereira CS, Lopes I, Sousa JP, Chelinho S. Effects of NaCl and seawater induced salinity on survival and reproduction of three soil invertebrate species. CHEMOSPHERE 2015; 135:116-122. [PMID: 25930052 DOI: 10.1016/j.chemosphere.2015.03.094] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Revised: 02/27/2015] [Accepted: 03/25/2015] [Indexed: 06/04/2023]
Abstract
The increase of global mean temperature is raising serious concerns worldwide due to its potential negative effects such as droughts and melting of glaciers and ice caps leading to sea level rise. Expected impacts on soil compartment include floodings, seawater intrusions and use of saltwater for irrigation, with unknown effects on soil ecosystems and their inhabitants. The present study aimed at evaluating the effects of salinisation on soil ecosystems due to sea level rise. The reproduction and mortality of three standard soil invertebrate species (Folsomia candida, Enchytraeus crypticus, Hypoaspis aculeifer) in standard artificial OECD soil spiked with serial dilutions of seawater/gradient of NaCl were evaluated according to standard guidelines. An increased sensitivity was observed in the following order: H. aculeifer≪E. crypticus≈F. candida consistent with the different exposure pathways: springtails and enchytraeids are exposed by ingestion and contact while mites are mainly exposed by ingestion due to a continuous and thick exoskeleton. Although small differences were observed in the calculated effect electrical conductivity values, seawater and NaCl induced the same overall effects (with a difference in the enchytraeid tests where a higher sensitivity was found in relation to NaCl). The adverse effects described in the present study are observed on soils not considered saline. Therefore, the actual limit to define saline soils (4000 μS cm(-1)) does not reflect the existing knowledge when considering soil fauna.
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Affiliation(s)
- C S Pereira
- CFE - Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, 3000-456 Coimbra, Portugal.
| | - I Lopes
- Department of Biology and CESAM, University of Aveiro, 3810-193 Aveiro, Portugal
| | - J P Sousa
- CFE - Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, 3000-456 Coimbra, Portugal
| | - S Chelinho
- CFE - Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, 3000-456 Coimbra, Portugal
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Fisker KV, Bouvrais H, Overgaard J, Schöttner K, Ipsen JH, Holmstrup M. Membrane properties of Enchytraeus albidus originating from contrasting environments: a comparative analysis. J Comp Physiol B 2015; 185:389-400. [DOI: 10.1007/s00360-015-0895-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2014] [Revised: 12/11/2014] [Accepted: 01/22/2015] [Indexed: 01/02/2023]
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Fisker KV, Holmstrup M, Malte H, Overgaard J. Effect of repeated freeze-thaw cycles on geographically different populations of the freeze-tolerant worm Enchytraeus albidus (Oligochaeta). J Exp Biol 2014; 217:3843-52. [PMID: 25214492 DOI: 10.1242/jeb.105650] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Freeze-tolerant organisms survive internal ice formation; however, the adaptations to repeated freeze-thaw cycles are often not well investigated. Here we report how three geographically different populations of Enchytraeus albidus (Germany, Iceland and Svalbard) respond to three temperature treatments - constant thawed (0°C), constant freezing (-5°C) and fluctuating temperature (0 to -5°C) - over a period of 42 days. Survival varied between treatments and populations such that enchytraeids from arctic locations had a higher survival following prolonged freeze periods compared with temperate populations. However, enchytraeids from temperate locations had the same survival rate as arctic populations when exposed to repeated freeze-thaw events. Across all populations, metabolic rate decreased markedly in frozen animals (-5°C) compared with thawed controls (0°C). This decrease is likely due to the lower temperature of frozen animals, but also to the transition to the frozen state per se. Animals exposed to repeated freeze-thaw events had an intermediate metabolic rate and freeze-thaw events were not associated with pronounced excess energetic costs. Overwintering under either condition was not associated with a decrease in lipid content; however, during exposure to constant freezing and repeated freeze-thaw events there was a noticeable decrease in carbohydrate stores over time. Thus, animals exposed to constant freezing showed a decrease in glycogen stores, while both glucose and glycogen content decreased over time when the organisms were exposed to repeated freezing. The results therefore suggest that carbohydrate resources are important as a fuel for E. albidus during freezing whereas lipid resources are of marginal importance.
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Affiliation(s)
- Karina Vincents Fisker
- Zoophysiology, Department of Bioscience, Aarhus University, Building 131, DK-8000 Aarhus C, Denmark Section of Soil Fauna Ecology and Ecotoxicology, Department of Bioscience, Aarhus University, Vejlsøvej 25, DK-8600 Silkeborg, Denmark
| | - Martin Holmstrup
- Section of Soil Fauna Ecology and Ecotoxicology, Department of Bioscience, Aarhus University, Vejlsøvej 25, DK-8600 Silkeborg, Denmark
| | - Hans Malte
- Zoophysiology, Department of Bioscience, Aarhus University, Building 131, DK-8000 Aarhus C, Denmark
| | - Johannes Overgaard
- Zoophysiology, Department of Bioscience, Aarhus University, Building 131, DK-8000 Aarhus C, Denmark
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Silva AP, Holmstrup M, Amorim M. Worms from the Arctic are better adapted to freezing and high salinity than worms from temperate regions: Oxidative stress responses in Enchytraeus albidus. Comp Biochem Physiol A Mol Integr Physiol 2013; 166:582-9. [DOI: 10.1016/j.cbpa.2013.09.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Revised: 09/03/2013] [Accepted: 09/03/2013] [Indexed: 01/23/2023]
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Roles of carbohydrate reserves for local adaptation to low temperatures in the freeze tolerant oligochaete Enchytraeus albidus. J Comp Physiol B 2013; 184:167-77. [PMID: 24154838 DOI: 10.1007/s00360-013-0788-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2013] [Revised: 10/10/2013] [Accepted: 10/10/2013] [Indexed: 10/26/2022]
Abstract
Geographic variation in cold tolerance and associated physiological adaptations were investigated in the freeze tolerant enchytraeid Enchytraeus albidus (Oligochaeta). Specimens from Svalbard, Greenland (Nuuk), Iceland (Hólar and Mossfellsbær) and continental Europe [Norway (Bergen), Sweden (Kullen) and Germany] were reared in the laboratory in a common-garden experiment. The aim was to test for variations in minimum lethal temperature, freeze duration tolerance, carbohydrate reserves and metabolic rate among the populations. Cold tolerance was related to environmental temperature of the respective location. Populations from the coldest climatic regions were able to tolerate freezing down to at least -15 °C and endured being frozen at -5 °C for 27-48 days, respectively. Populations from milder climates had a lower freeze duration tolerance (about -9 °C) and endured -5 °C for a shorter period (between 9 and 16 days). Glucose accumulation and glycogen reserves varied significantly between populations, but was not related directly to cold tolerance. Metabolic rate varied significantly between populations, but was not significantly related to cold tolerance. The metabolic rates at -2 °C of frozen and unfrozen worms from Germany and Svalbard were tested. The metabolic depression due to freezing of these populations was relatively small (<50 %), suggesting that the large carbohydrate accumulations may also be important as fuel during long-term freezing at moderately low temperatures. Differences in metabolic depression may partly explain the difference in cold tolerance of these two populations, however, the mechanisms behind local adaptation to low winter temperatures in these enchytraeid populations seem more complex than earlier studies have indicated.
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