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  1. Article: Comparison of sterol and fatty acid profiles of chytrids and their hosts reveals trophic upgrading of nutritionally inadequate phytoplankton by fungal parasites

    gerphagnon, Mélanie / Agha, Ramsy / Martin-Creuzburg, Dominik / Bec, Alexandre / Gachon, Claire / Wolinska, Justyna

    Environmental microbiology, 21(3):949-58

    2018  

    Abstract: Chytrids are ubiquitous fungal parasites in aquatic ecosystems, infecting representatives of all major phytoplankton groups. They repack carbon from inedible phytoplankton hosts into easily ingested chytrid propagules (zoospores), rendering this carbon ... ...

    Institution Leibniz-Institut für Gewässerökologie und Binnenfischerei
    Abstract Chytrids are ubiquitous fungal parasites in aquatic ecosystems, infecting representatives of all major phytoplankton groups. They repack carbon from inedible phytoplankton hosts into easily ingested chytrid propagules (zoospores), rendering this carbon accessible to zooplankton. Grazing on zoospores may circumvent bottlenecks in carbon transfer imposed by the dominance of inedible or poorly nutritious phytoplankton (mycoloop). We explored qualitative aspects of the mycoloop by analysing lipid profiles (fatty acids, sterols) of two chytrids infecting two major bloom‐forming phytoplankton taxa of contrasting nutritional value: the diatom Asterionella formosa and the filamentous cyanobacterium Planktothrix agardhii. The polyunsaturated fatty acid composition of chytrids largely reflected that of their hosts, highlighting their role as conveyors of otherwise inaccessible essential lipids to higher trophic levels. We also showed that chytrids are capable of synthesizing sterols, thus providing a source of these essential nutrients for grazers even when sterols are absent in their phytoplankton hosts. Our findings reveal novel qualitative facets of the mycoloop, showing that parasitic chytrids, in addition to making carbon and essential lipids available from inedible sources, also upgrade their host's biochemical composition by producing sterols de novo, thereby enhancing carbon and energy fluxes in aquatic food webs.
    Language English
    Document type Article
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  2. Article ; Online: Food quality shapes gradual phenotypic plasticity in ectotherms facing temperature variability.

    Van Baelen, Marine / Bec, Alexandre / Sperfeld, Erik / Frizot, Nathan / Koussoroplis, Apostolos-Manuel

    Ecology

    2024  Volume 105, Issue 4, Page(s) e4263

    Abstract: Organisms exhibit reversible physiological adjustments as a response to rapidly changing environments. Yet such plasticity of the phenotype is gradual and may lag behind environmental fluctuations, thereby affecting long-term average performance of the ... ...

    Abstract Organisms exhibit reversible physiological adjustments as a response to rapidly changing environments. Yet such plasticity of the phenotype is gradual and may lag behind environmental fluctuations, thereby affecting long-term average performance of the organisms. By supplying energy and essential compounds for optimal tissue building, food determines the range of possible phenotypic changes and potentially the rate at which they occur. Here, we assess how differences in the dietary supply of essential lipids modulate the phenotypic plasticity of an ectotherm facing thermal fluctuations. We use three phytoplankton strains to create a gradient of polyunsaturated fatty acid and sterol supply for Daphnia magna under constant and fluctuating temperatures. We used three different fluctuation periodicities to unravel the temporal dynamics of gradual plasticity and its long-term consequences for D. magna performance measured as juvenile somatic growth rate. In agreement with gradual plasticity theory, we show that in D. magna, fluctuation periodicity determines the differential between observed growth rates and those expected from constant conditions. Most importantly, we show that diet modulates both the size and the direction of the growth rate differential. Overall, we demonstrate that the nutritional context is essential for predicting ectotherm consumers' performance in fluctuating thermal environments.
    MeSH term(s) Animals ; Temperature ; Adaptation, Physiological ; Phenotype ; Food ; Food Quality ; Daphnia/physiology
    Language English
    Publishing date 2024-02-22
    Publishing country United States
    Document type Journal Article
    ZDB-ID 2010140-5
    ISSN 1939-9170 ; 0012-9658
    ISSN (online) 1939-9170
    ISSN 0012-9658
    DOI 10.1002/ecy.4263
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  3. Article ; Online: Utilization of basal resources in a forested headwater stream: a combined stable isotope and fatty acid approach

    Labed-Veydert, Tiphaine / Bec, Alexandre / Perrière, Fanny / Desvilettes, Christian

    Aquat Sci. 2023 Jan., v. 85, no. 1 p.13-13

    2023  

    Abstract: In mountainous areas, forest headwater streams are characterized by a predominantly heterotrophic functioning resulting from massive seasonal allochthonous litter input. However, autochthonous primary production can contribute significantly to energy ... ...

    Abstract In mountainous areas, forest headwater streams are characterized by a predominantly heterotrophic functioning resulting from massive seasonal allochthonous litter input. However, autochthonous primary production can contribute significantly to energy fluxes when canopies are open and in exposed stream reaches. Understanding whether this contribution tends to be limited to a supplementary supply of essential nutrients such as polyunsaturated fatty acids (PUFAs) or whether it supports the whole food web is a central theme in freshwater ecology. We carried out seasonal monitoring in a forest stream near its main source during the period of increasing secondary production (April-November). Combining stable isotopes (¹³C-¹⁵N) and fatty acid analyses, we found that autochthonous primary production constituted the leading resource for five specific macroinvertebrate taxa in spring and summer. The leaf litter deposits were monospecific (Fagus sylvatica) and proved to be poorly used. In contrast, fine benthic organic matter (FBOM), mostly produced from leaf litter degradation, provided a significant source of quality food used by primary consumers (Gammarus pulex, Ecdyonorus sp. and Leuctra spp.). Our data analysis confirms that epilithic and epixylic biofilms (associated with FBOM) were the source of the essential PUFAs (20:4ω6 and 20:5ω3), assimilated by the macroinvertebrate studied. Furthermore, at some period, the predatory taxa (Isoperla ambigua and Rhyacophila spp.) also derived 20:4ω6 and 20:5ω3 from the direct ingestion of microalgae. Despite their formal functional feeding group, all the macroinvertebrate taxa tended to be opportunistic omnivores that relied on all available resources.
    Keywords Fagus sylvatica ; Gammarus pulex ; Isoperla ; Leuctra ; Rhyacophila ; biofilm ; energy ; fatty acids ; food webs ; forests ; ingestion ; limnology ; macroinvertebrates ; microalgae ; mountains ; organic matter ; plant litter ; primary productivity ; spring ; stable isotopes ; streams ; summer ; water
    Language English
    Dates of publication 2023-01
    Size p. 13.
    Publishing place Springer International Publishing
    Document type Article ; Online
    ZDB-ID 1464021-1
    ISSN 1420-9055 ; 1015-1621
    ISSN (online) 1420-9055
    ISSN 1015-1621
    DOI 10.1007/s00027-022-00906-y
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  4. Article ; Online: Dietary sterol availability modulates heat tolerance of Daphnia

    Koussoroplis, Apostolos‐Manuel / Sperfeld, Erik / Pincebourde, Sylvain / Bec, Alexandre / Wacker, Alexander

    Freshwater Biology. 2023 Mar., v. 68, no. 3 p.452-461

    2023  

    Abstract: The increasing frequency and intensity of summer heatwaves are pushing freshwater zooplankton towards their upper thermal tolerance limits. At the same time, higher temperatures and prolonged water column stratification can favour the dominance of ... ...

    Abstract The increasing frequency and intensity of summer heatwaves are pushing freshwater zooplankton towards their upper thermal tolerance limits. At the same time, higher temperatures and prolonged water column stratification can favour the dominance of cyanobacteria in phytoplankton. Even when not toxic or grazing resistant, these prokaryotes lack phytosterols as essential precursors for cholesterol, the main sterol in animal tissues. Cholesterol plays a crucial role in the physiological adaptation of ectotherms to high temperature. Therefore, the shift to cyanobacteria‐dominated systems may increase the vulnerability of zooplankton to heatwaves by intensifying cholesterol limitation. Here, we used death time curves that take into consideration the intensity and duration of a thermal challenge and a dynamic model to study the effects of cholesterol limitation on the heat tolerance of the keystone species Daphnia magna and to simulate the cumulative mortality that could occur in a fluctuating environment over several days of heatwave. We show that increasing cholesterol limitation does not affect the slope between time‐to‐immobilisation and temperature, but does decrease the maximal temperature that Daphnia can withstand by up to 0.74°C. This seemingly small difference is sufficient to halve the time individuals can survive heat stress. Our simulations predicted that, when facing heatwaves over several days, the differences in survival caused by cholesterol limitation build up rapidly. Considering the anticipated intensity and duration of future (2070–2099) heatwaves, cholesterol limitation could increase mortality by up to 45% and 72% under low and medium greenhouse gas emission scenarios, respectively. These results suggest that the increasing risk of cholesterol limitation due to more frequent cyanobacterial blooms could compromise the resistance of zooplankton populations to future heatwaves. More generally, this study shows the importance of considering the nutritional context in any attempt to predict ectotherm mortality with increasing temperatures in the field.
    Keywords Daphnia magna ; animals ; cholesterol ; death ; dynamic models ; ectothermy ; freshwater ; greenhouse gas emissions ; heat stress ; heat tolerance ; keystone species ; limnology ; mortality ; phytoplankton ; phytosterols ; prokaryotic cells ; risk ; summer ; temperature ; toxicity ; zooplankton
    Language English
    Dates of publication 2023-03
    Size p. 452-461.
    Publishing place John Wiley & Sons, Ltd
    Document type Article ; Online
    Note JOURNAL ARTICLE
    ZDB-ID 121180-8
    ISSN 0046-5070
    ISSN 0046-5070
    DOI 10.1111/fwb.14037
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  5. Article ; Online: The energetic cost of facing cyanotoxins: a case study on Daphnia magna

    Ruiz, Thomas / Koussoroplis, Apostolos-Manuel / Latour, Delphine / Bec, Alexandre

    Aquat Ecol. 2023 Mar., v. 57, no. 1 p.15-20

    2023  

    Abstract: Under the effects of global change, toxic cyanobacterial proliferations increase and subsequently threaten freshwater ecosystems and the services they provide. Zooplankton consumers, a key trophic level of freshwater ecosystems, are particularly impaired ...

    Abstract Under the effects of global change, toxic cyanobacterial proliferations increase and subsequently threaten freshwater ecosystems and the services they provide. Zooplankton consumers, a key trophic level of freshwater ecosystems, are particularly impaired by cyanotoxins, but populations regularly exposed to cyanobacteria can develop tolerance against toxins. While the physiological processes involved in this tolerance have been extensively studied, their consequences for consumers’ energetics remain poorly explored, impeding predictions of energy flow from zooplankton up to higher trophic levels. Here, we explored the metabolic response of Daphnia magna exposed to toxic and non-toxic strains of cyanobacteria to define the energy dedicated to cyanotoxins resistance mechanisms. We showed that resting metabolic rate (RMR) of individuals exposed to toxins increased by up to 60%, reflecting the energy requirement involved by cyanotoxin resistance processes. By quantifying the energy dedicated to resistance mechanisms, RMR constitutes an interesting metric to estimate overall capacity of individual zooplankters to actively handle cyanotoxins. Moreover, RMR responds more promptly to cyanotoxins than growth thus being adequate to assess short-term cyanotoxins constraints (< 72 h). Overall, we showed that cyanotoxins resistance constitutes an energy leak in freshwater ecosystems. Quantifying this leak of energy may help anticipate alterations of energy flow within food web in response to cyanobacterial proliferation and, ultimately, enhance our predictions of freshwater ecosystem structure and functions in a context of global change.
    Keywords Cyanobacteria ; Daphnia magna ; biochemical pathways ; case studies ; cyanobacterial toxins ; energy flow ; freshwater ; freshwater ecosystems ; global change ; metabolism ; toxicity ; trophic levels ; zooplankton
    Language English
    Dates of publication 2023-03
    Size p. 15-20.
    Publishing place Springer Netherlands
    Document type Article ; Online
    ZDB-ID 1411979-1
    ISSN 1573-5125 ; 1386-2588
    ISSN (online) 1573-5125
    ISSN 1386-2588
    DOI 10.1007/s10452-022-09990-6
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  6. Article: Questioning the roles of resources nutritional quality in ecology

    Danger, Michael / Bec, Alexandre / Spitz, Jérôme / Perga, Marie‐Elodie

    Oikos. 2022 July, v. 2022, no. 7

    2022  

    Abstract: Our understanding of ecosystem functioning is strongly linked to the study of predator–prey relationships and food web structures. However, trophic ecology has often focused on identifying taxonomic relationships and quantifying the biomass or energy ... ...

    Abstract Our understanding of ecosystem functioning is strongly linked to the study of predator–prey relationships and food web structures. However, trophic ecology has often focused on identifying taxonomic relationships and quantifying the biomass or energy ingested by consumers, but has often failed to integrate the importance of the nutritional quality of resources in ecological dynamics. Underlying this gap is the multi‐dimensional nature of resource quality which has hampered any consensus on the definition of resource nutritional quality. In this special issue, we aimed at gathering a subset of articles exemplifying the diversity of variables by which resources quality is quantified, the diversity of research topics that can be tackled in ecology – from physiological or evolutionary aspects to ecosystem processes – and propose some perspectives on the integration of nutritional quality within broader ecological concepts. Using a semi‐automated literature analysis, we map the current landscape of the ‘resources nutritional quality' research of the last 30 years. We depict how it has been quantified through physical, biological or chemical indicators, the use of these parameters being largely dependent on the type of ecosystem studied and on the investigated ecological process. We then position the articles published in this special issue of Oikos within this landscape, showing they cover a small but relatively well representative subset of the domains of resources quality‐related issues. Articles in this special issue browse a range of individual and population‐level approaches (embracing evolutionary questions) to community related questions, include methodological issues and ecosystem‐wide approaches using trophic quality indicators as tracers of resources origin. Based on these studies and on the literature review, we identify a non‐exhaustive list of challenges and perspectives of research that we consider of highest priority in the large topic of trophic ecology.
    Keywords biomass ; ecosystems ; energy ; food webs ; landscapes ; nutritive value
    Language English
    Dates of publication 2022-07
    Publishing place Blackwell Publishing Ltd
    Document type Article
    Note JOURNAL ARTICLE
    ZDB-ID 207359-6
    ISSN 0030-1299
    ISSN 0030-1299
    DOI 10.1111/oik.09503
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  7. Article: Upstream/downstream food quality differences in a Caribbean Island River

    Frotté, Lou / Bec, Alexandre / Hubas, Cédric / Perrière, Fanny / Cordonnier, Sébastien / Bezault, Etienne / Monti, Dominique

    Aquatic ecology. 2022 Mar., v. 56, no. 1

    2022  

    Abstract: Caribbean rivers are inhabited by native macrofauna with a diadromous life cycle. The factors influencing the upstream migration of diadromous species are not well understood. Suggested primary factors include species density, habitat suitability and ... ...

    Abstract Caribbean rivers are inhabited by native macrofauna with a diadromous life cycle. The factors influencing the upstream migration of diadromous species are not well understood. Suggested primary factors include species density, habitat suitability and food availability. We hypothesized that food quality could be a key parameter in the upstream migration of macrocrustaceans. We sampled the main shrimp species and their potential food sources along an altitudinal gradient in the Grand Carbet River of Guadeloupe. Lipid analyses of the different food items reveal that biofilm and drifting organic matter are main sources of eicosapentaenoic acid (EPA). Biofilm is richer in EPA upstream, while drifting material is richer in EPA downstream. These opposed altitudinal gradients are reflected in shrimp lipids depending on whether they feed on biofilm or drifting organic matter. In addition, low EPA levels in shrimp suggest that dietary EPA could be a limiting factor in this system and that this differential altitudinal distribution of EPA could influence shrimp settlement.
    Keywords altitude ; biofilm ; diadromous fish ; eicosapentaenoic acid ; fauna ; food availability ; food quality ; habitats ; organic matter ; rivers ; shrimp ; Caribbean ; Guadeloupe
    Language English
    Dates of publication 2022-03
    Size p. 311-317.
    Publishing place Springer Netherlands
    Document type Article
    ZDB-ID 1411979-1
    ISSN 1573-5125 ; 1386-2588
    ISSN (online) 1573-5125
    ISSN 1386-2588
    DOI 10.1007/s10452-021-09887-w
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  8. Article ; Online: Nutritional context modulates the salinity tolerance of freshwater invertebrates

    Ruiz, Thomas / Koussoroplis, Apostolos-Manuel / Felten, Vincent / Bec, Alexandre

    Aquat Ecol. 2022 Dec., v. 56, no. 4 p.905-915

    2022  

    Abstract: Food quality is known as a major driver of organisms’ performances, but the way it may modulate the response of consumers to environmental stressors now appears as critical issue of trophic ecology. Here we evaluated whether and how food quality mediates ...

    Abstract Food quality is known as a major driver of organisms’ performances, but the way it may modulate the response of consumers to environmental stressors now appears as critical issue of trophic ecology. Here we evaluated whether and how food quality mediates the salinity tolerance of the model organism Daphnia magna to assess the resistance of zooplankton populations to salinization, which constitutes a serious threat for freshwater ecosystems worldwide. We showed that diets lacking highly unsaturated fatty acids (HUFA) and sterols reduce the salinity tolerance range of daphnids by more than 30%. Our measurements of individual metabolic rate coupled with the quantification of consumers NaCl body content revealed that this reduction in salinity tolerance arises either from an increased energetic cost of iono-/osmo-regulation when food quality declines or from a lower resistance to NaCl when consumers lack sterols and highly unsaturated fatty acids (HUFA). While improving individual salt tolerance, these two mechanisms may have opposite consequences at ecosystem scale and need to be fully considered when predictions of consumers responses to multifactorial stresses are induced by global change.
    Keywords Daphnia magna ; ecosystems ; food quality ; freshwater ; global change ; metabolism ; salt tolerance ; sterols ; zooplankton
    Language English
    Dates of publication 2022-12
    Size p. 905-915.
    Publishing place Springer Netherlands
    Document type Article ; Online
    ZDB-ID 1411979-1
    ISSN 1573-5125 ; 1386-2588
    ISSN (online) 1573-5125
    ISSN 1386-2588
    DOI 10.1007/s10452-022-09975-5
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  9. Article: Early spring food resources and the trophic structure of macroinvertebrates in a small headwater stream as revealed by bulk and fatty acid stable isotope analysis

    Labed-Veydert, Tiphaine / Koussoroplis, Apostolos-Manuel / Bec, Alexandre / Desvilettes, Christian

    Hydrobiologia. 2021 Dec., v. 848, no. 21

    2021  

    Abstract: Energy and organic matter flow in forested headwater stream trophic webs is generally more dependent on allochthonous than autochthonous organic matter. However, we propose that autochthonous organic matter significantly contributes to the development of ...

    Abstract Energy and organic matter flow in forested headwater stream trophic webs is generally more dependent on allochthonous than autochthonous organic matter. However, we propose that autochthonous organic matter significantly contributes to the development of primary consumers during periods when the riparian canopy is open. We determined bulk stable isotope signatures, fatty acid (FA) composition and carbon stable isotope ratios of individual FA (δ¹³CFA) of basal organic sources and nine major macroinvertebrate taxa sampled in a first-order forest stream (Massif Central, France) in early spring before the onset of vegetation growth. Our results from a Bayesian mixing model showed that most of the energy channeled to invertebrate consumers came from biofilm, bryophytes and fine benthic detrital particles (FBOM), and little from beech leaf litter. Estimates from a model using proportions of assimilated sources and δ¹³CFA signatures showed that the most common FAs (i.e. 16:0, 18:3ω3) were derived from organic sources proportionally relative to their assimilation by macroinvertebrates. In addition, it was clear that long-chain PUFAs (ARA and EPA) were obtained only from autochthonous sources through flexible feeding strategies. Our study highlights the dependence of stream macroinvertebrates on autochthonous primary production (including bryophytes) for their long-chain PUFA requirement.
    Keywords Bayesian theory ; Fagus ; aquatic invertebrates ; biofilm ; canopy ; energy ; forests ; macroinvertebrates ; organic matter ; plant litter ; primary productivity ; spring ; stable isotopes ; streams ; France
    Language English
    Dates of publication 2021-12
    Size p. 5147-5167.
    Publishing place Springer International Publishing
    Document type Article
    ZDB-ID 214428-1
    ISSN 1573-5117 ; 0018-8158
    ISSN (online) 1573-5117
    ISSN 0018-8158
    DOI 10.1007/s10750-021-04699-3
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  10. Article: Microalgal food sources greatly improve macroinvertebrate growth in detritus‐based headwater streams: Evidence from an instream experiment

    Labed‐Veydert, Tiphaine / Danger, Michael / Felten, Vincent / Bec, Alexandre / Laviale, Martin / Cellamare, Maria / Desvilettes, Christian

    Freshwater biology. 2022 Aug., v. 67, no. 8

    2022  

    Abstract: In forested headwater streams, inconspicuous food resources such as epilithic microalgae can play a major role owing to their content of long chain polyunsaturated fatty acids (PUFAs) that are essential for macroinvertebrate development. Yet, the use of ... ...

    Abstract In forested headwater streams, inconspicuous food resources such as epilithic microalgae can play a major role owing to their content of long chain polyunsaturated fatty acids (PUFAs) that are essential for macroinvertebrate development. Yet, the use of these resources and their consequences for consumers and life‐history traits remain scarcely studied, especially for non‐herbivorous taxa. Using instream mesocosms, we aimed to understand how two macroinvertebrate species, a shredder detritivore (Gammarus pulex) and a scraper (Rhithrogena semicolorata), use available organic resources under light versus shaded conditions (high and low amounts of phototrophic biofilm, respectively). We specifically focused on the origin of carbon (C) and essential lipids (PUFAs, sterols) assimilated by the two species and the effects of these compounds on their survival and growth. When autotrophic biofilms were available (mesocosms exposed to light), both species experienced significantly higher growth than in mesocosms placed in the dark. In Rhithrogena nymphs, the survival and imago emergence rates were positively affected by access to autotrophic biofilms. Using stable isotope analysis (δ¹³C and δ¹⁵N), we demonstrated that under dark conditions both macroinvertebrates assimilated C of detrital origin. Under light conditions, most of the C assimilated by R. semicolorata was derived from autotrophic biofilms and around 11% from fine detrital particles (FPOM). Gammarus pulex derived part of its C from detrital sources (mainly FPOM) and from autotrophic biofilms. The results of isotopic analyses (δ¹³C) on fatty acids (FAs) and sterols showed that the scraper Rhithrogena was entirely dependent on autotrophic biofilms to meet its dietary FAs and sterol requirements. In contrast, detrital sources were quantitatively important for G. pulex both in terms of C and sterol supply, irrespective of the conditions tested. For these consumers, microalgae seemed to be a complementary food source, but yet essential to cover a large part of their requirements in long‐chain PUFAs. This study clearly confirmed the ecological importance of autotrophic biofilms for two functional feeding groups of macroinvertebrates in headwater streams providing new insights on the trophic origin of sterols and long‐chain PUFAs in their diet.
    Keywords Gammarus pulex ; Rhithrogena ; biofilm ; carbon ; complementary foods ; detritivores ; diet ; imagos ; life history ; limnology ; macroinvertebrates ; microalgae ; stable isotopes ; sterols ; water
    Language English
    Dates of publication 2022-08
    Size p. 1380-1394.
    Publishing place John Wiley & Sons, Ltd
    Document type Article
    Note JOURNAL ARTICLE
    ZDB-ID 121180-8
    ISSN 0046-5070
    ISSN 0046-5070
    DOI 10.1111/fwb.13924
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