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Les articles de Delphine Nicolas
de Delphine Nicolas, Baptiste Testi, Dušan Jesenšek, Kim Leban, Alain J. Crivelli
In Ecohydrology, (en ligne) (October, 2025), 100705
En ligne : www.sciencedirect.com[...]
Temporal data series of water temperature collected at various locations in the Upper Soča river basin, a pristine area in Slovenia, from 1996 to 2022, were analyzed to assess any trends as potential effects of the global change. Different temperature metrics were calculated to study more especially eventual impacts on trout species known as present in the target sites: the endemic marble trout (Salmo marmoratus), the introduced common trout (Salmo trutta) and hybrid trout (S. marmoratus x S. trutta). Significant trends were observed in more than half of the streams considered, indicating a general warming of water temperatures across the entire Upper Soča basin. The high regional coherence found for streams in the three watersheds (Soča, Bača and Idrijca) studied suggested regional synchrony and an overall predominant climatic influence. However, a greater variation was observed in spring and summer, suggesting the implications of additional local factors. The majority of the monitored sites (n = 18 out of 25) experienced an increase in the annual mean temperature (+ 0.04 °C per year on average), especially in summer (+0.1 °C per year on average for 19 sites) when flows were lower. Thermal conditions remained favourable for salmonids in all sites. However, temperatures above 15 °C or even 19 °C are expected to be increasingly recorded, enhancing periods with stressful conditions for salmonids, at first for the endemic S. marmoratus.
de Justine Boutry, Mathieu Douhard, Klara Asselin, Antoine M. Dujon, Jordan Meliani, Olivier De Backer, Delphine Nicolas, Aaron G. Schultz, Peter A. Biro, Christa Beckmann, et al.
In Ecology and Evolution, 15(9) (September, 2025), e72003
En ligne : onlinelibrary.wiley.com[...]
Offspring sex ratio has been proposed as an indicator of the risk of developing certain cancers in humans, but offspring sex ratio may also be a consequence of the disease. In this study, we investigate this subject using the zebrafish, Danio rerio, as a model system. First, we explore whether inducing skin cancer at an early stage of the host's life (embryonic stage) has the potential to influence sex determination and/or sex-specific mortality. Second, we investigate whether the sex ratio in offspring produced by tumor-bearing adult females differs from that of healthy females. Third, we compare the survival (until sexual maturity) of offspring produced by cancerous and non-cancerous females. We found that skin cancer did not influence sex determination and the sex ratio of the offspring. However, consistent with previous studies on other model systems, the survival of offspring was higher when mothers were cancerous, suggesting that diseased females allocate more resources to current reproductive effort compared to their healthy counterparts. This study makes a significant contribution to our understanding of the ecological and evolutionary consequences of host-tumor interactions in animals.
de Audrey Arnal, Erika Burioli, Lisa Jacquin, Sophie Labrut, Stéphane Duchon, Marie Rossignol, Delphine Nicolas, Beata Ujvari, Antoine Dujon, Jordan Meliani, et al.
In Ecotoxicology and Environmental Safety, 301 (August, 2025), 118449
En ligne : www.sciencedirect.com[...]
Malathion is a widely used pesticide with potentially oncogenic properties and may have deleterious effects on organism health and fitness. Although malathion use is now restricted in the European Union, it remains widely used for public health campaigns in other parts of the world, particularly for mosquito control. Understanding its sublethal and long-term effects is thus essential, both for evaluating its ecotoxicological impacts and for anticipating resistance mechanisms. However, empiric data on its effects in wild organisms - especially in invertebrates - remain limited. Here, we quantitatively investigated whether larval exposure to environmentally realistic concentrations of malathion could affect mosquito tissue structure and gene expression profiles of adult Aedes aegypti (yellow fever mosquitoes), using both RNA-seq and histological approaches. Results show no neoplastic or pre-neoplastic lesions in adults exposed to malathion during larval development, contrary to previous studies in other organisms showing carcinogenic effects of malathion. However, our differential gene expression analyses revealed significant changes in genes related to mitochondrial function, energy metabolism, and detoxification pathways, suggesting significant physiological impacts of malathion in adults after early-life pesticide exposure. Notably, females exhibited stronger transcriptomic responses than males, including the upregulation of genes involved in detoxification (e.g., P450 cytochromes), olfactory perception, and stress response, with potential consequences for resistance mechanisms. Our findings underscore the ability of mosquitoes to mount transient molecular responses to environmental pollutants, potentially contributing to the long-term selection of metabolic resistance traits – an outcome with important implications for vector control strategies.
de Théo Deremarque, Rodolphe Elie Gozlan, Ravo Ravaozafindrasoa, Giuliano Mucci, Lucie Delalex, Jean-Michel Foissy, Michael Cagnant, Mathieu Clair, Justina Givens, Fabienne Justy, et al.
In Water Biology and Security, (en ligne) (May, 2025), 100423
En ligne : www.sciencedirect.com[...]
eDNA-based methods offer a non-invasive, easy-to-use approach for monitoring aquatic biodiversity, particularly for tracking invasive or cryptic species. While Illumina sequencing is commonly used, few studies have explored pairing eDNA sampling with Nanopore sequencing, a third-generation technology that allows for on-site sequencing but with a higher error rate. Here, we compared the performance of both technologies in detecting the invasive host-parasite complex Pseudorasbora parva-Sphaerothecum destruens. Water samples were collected from sites in Camargue and Corsica (Southern France), followed by DNA extraction, PCR amplification, and sequencing using either Illumina or Nanopore. Both technologies showed similar detection rates of P. parva, but only when Nanopore sequencing was performed under optimal conditions. However, for S. destruens, results varied: Illumina failed to detect the parasite, while Nanopore identified its DNA in multiple sites. We suggest that this discrepancy may be due to the different bioinformatic approaches used to process the reads and/or the higher error rate of Nanopore sequencing which could result in misassignments during species identification.
de Amélie Hoste, Raphaël Lagarde, Elsa Amilhat, Colin Bouchard, Paco Bustamante, Adrian Covaci, Elisabeth Faliex, Emmanuelle Migne, Giulia Poma, Claire Tetrel, et al.
In Environmental Science and Pollution Research, (en ligne) (January, 2025)
En ligne : doi.org[...]
Coastal lagoons are diverse habitats with significant ecological gradients, which provide crucial ecosystem services but face threats from human activities such as invasive species and pollution. Among the species inhabiting the lagoons, the critically endangered European eel (Anguilla anguilla) is an emblematic species strongly impacted by contamination and parasitism. Several indicators were developed to assess the quality of eel at a large geographic scale. Most indicators are based on the concentration of individual pollutant and/or abundance of parasites separately without considering individual variations. This study assessed the quality of 59 eels captured at three different sites inside a Mediterranean lagoon complex (the Camargue, South of France), by integrating multiple degradation factors (POPs, TEs, and A. crassus infestation) and considering individual eel characteristics (length, age, growth rate, and sex). Using multivariate TOPSIS analysis including these degradation factors, this study found that eel quality decreased with age but did not significantly vary between sites. When focusing on each degradation factor, A. crassus infestation rates were lower in older eels, independently to the site; however, the POPs and TEs contaminations were lower in the Grandes Cabanes site compared to the Vaccarès and Fumemorte sites even if smaller and younger eels were more contaminated by POPs. These findings reveal the fine-scale spatial variability in eel quality, with TOPSIS analysis providing a robust method to rank and score scenarios. This approach enhances the understanding of habitat degradation sources affecting eel contamination and parasitic infestation, supporting more effective strategies for sustainable habitat management.
de Jacques Panfili, Delphine Nicolas, Khady Diop, Alain J. Crivelli
In Marine and Freshwater Research, 75(18) (December, 2024)
En ligne : www.publish.csiro.au[...]
The invasive wels catfish is spreading to many European waterbodies and is the subject of controversy concerning its environmental impact.The objective was to investigate its life-history traits (growth and reproduction) for the first time in southern France. A culling action was used to assess the key life-history traits, using sections of pectoral spines for age and growth estimations, and gonad macroscopic examination for the reproduction parameters. The biggest individual was a 227-cm male. The age was accurately estimated from clear translucent marks on spines, with a maximum of 13years for both sexes. The growth appeared to be extremely rapid and was the highest at old ages recorded from both the native and the invasive distribution range. The length and age at first sexual maturity, 70.1cm for 4–5-year-old females, and 54.1cm for 2–3-year-old males, were the lowest recorded in Europe, indicating an early maturity. The life-history parameters (rapid growth, early maturation, high fecundity) showed a very high potential for adaptation and colonisation. The cost and management required to regulate the species appear not easily feasible, particularly when combined with its high growth rate.
de Théo Deremarque, Rodolphe Elie Gozlan, Ravo Ravaozafindrasoa, Giuliano Mucci, Lucie Delalex, Jean-Michel Foissy, Michael Cagnant, Mathieu Clair, Justina Givens, Fabienne Justy, et al.
In Fishes, 9(12) (December, 2024), 477
En ligne : www.mdpi.com[...]
The spread of non-native species threatens biodiversity and exacerbates societal challenges like food security. To address this, effective conservation programs require detection methods that are easy to implement, accurate, and non-invasive. Over the past 15 years, environmental DNA (eDNA) techniques have gained popularity, surpassing traditional sampling methods. In this context, our study focused on tracking the invasive host–pathogen complex Pseudorasbora parva and Sphaerothecum destruens using eDNA metabarcoding. We collected water samples from freshwater canals over five months in the Camargue region, and once in Corsica Island, both in southern France. Total DNA was extracted from filtered water samples, and PCR-amplicons were sequenced using Illumina or Nanopore technologies. Our results revealed a high detection rate of P. parva in lentic ecosystems, aligning with habitat preferences of this small freshwater fish. Additionally, the detection rate in Camargue increased in May and June, likely due to the peak of the spawning season, which leads to more DNA being released into the environment (i.e., concentration and interaction of individuals). While eDNA successfully detected this invasive fish, we were unable to detect its cryptic fungal parasite, S. destruens, highlighting the challenges of identifying intracellular and cryptic fungal pathogens through eDNA methods.
de Amélie Hoste, Colin Bouchard, Jean-Christophe Poggiale, Delphine Nicolas
In Journal of Fish Biology, Online version (October, 2024)
En ligne : onlinelibrary.wiley.com[...]
Since the 1980s, the European eel (Anguilla anguilla) has declined by over 90% in recruitment across its European and North African distribution area. This diadromous fish spawns at sea and migrates into continental waters, where it grows for three to more than 30 years, depending on habitat conditions and location. During their growth, different habitat use tactics can locally influence the life-history traits of eels, including their survival rates. Thus, the spatio-temporal dimension of this species is crucial for management. Based on a rare Mediterranean long-term survey of more than 20 years (2001–2022) in an artificial drainage canal connected to a vast brackish lagoon (the Vaccarès lagoon), we aimed to study the dynamics of one subpopulation's life-history traits. We used Bayesian multistate capture-mark-recapture (CMR) models to assess the temporal variability in survival and abundance at both seasonal and inter-annual scales, considering life-stage structure. High survival rates and low detection probabilities were found for the undifferentiated and female yellow stages. In contrast, female silver eels exhibited lower survival rates and higher capture probabilities. Estimating detection probabilities and survival rates enabled accurate assessment of relative abundance across different life stages and time periods. Our findings indicated a substantial decrease in the abundance of undifferentiated and female yellow eels in the early 2000s, whereas the abundance of female silver eels remained consistently low yet stable throughout the study period. Considering the life stage seemed essential to study the dynamics of the eel during its continental growing period. The present results will provide key elements to propose and implement suitable sustainable environmental management strategies for eel conservation.Estimating migration speed of glass eels during their colonization of a Mediterranean lagoon
de Colin Bouchard, Delphine Nicolas
In Journal of Fish Biology, 103(5) (November, 2023), 9
En ligne : onlinelibrary.wiley.com[...]
Migration speed can have important evolutionary consequences as it can affect the timing of arrival, remaining energy reserves, and habitat choice. Environmental conditions and individual phenotypic traits can impact the migration speed of individuals. In this way, estimating migration speed is of particular importance, especially for species under strong management strategies and colonizing highly diversified habitats, as is the case for the European eel. However, estimating the migration speed of glass eels, which is the life stage when eels colonize continental habitats, presents challenges due to typically low re-capture probabilities and difficulties in tagging individuals. Using recruitment time series at two sites, one at the sea connection and another inland, we estimated the temporal lag between the two migration peaks to compute migration speed. Because we worked on the Mediterranean coasts and in a lagoon, the weak tidal amplitudes may inhibit individuals from efficiently performing the selective tidal stream transport. We obtained migration speed values coherent with the few values available in the literature for Atlantic estuaries. The values we obtained that are lower than those obtained for Atlantic estuaries are also coherent with the weak tides along the Mediterranean coasts and lead to necessary further studies to understand the migratory behavior of glass eels in such hydro-systems.
de Paul Castagné, Ivan Paz-Vinas, Stéphanie Boulêtreau, Jessica Ferriol, Geraldine Loot, Charlotte Veyssière, Robert Arlinghaus, Robert Britton, Marlène Chiarello, Emili Garcia-Berthou, et al.
In Biodiversity and conservation, Online April (April, 2023)
En ligne : link.springer.com[...]
Biological invasions are a major component of global change worldwide. But paradoxically, an invasive species might also have threatened populations within its native range. Designing efficient management policies is needed to prevent and mitigate range expansions of invasive alien species (IAS) in non-native areas, while protecting them within their native range. Characterizing genetic variation patterns for IAS populations and deciphering the links between their native and introduced populations is helpful to (i) assess the genetic state of both native and non-native populations, (ii) reveal potential invasion pathways, (iii) define IAS management strategies in invaded areas, and (iv) identify native populations requiring conservation measures. The European catfish (Silurus glanis) is the largest European predatory fish. Introduced since the seventies from Eastern to Western Europe, it has colonized many waterbodies. Yet, little is known about the genetic status of non-native populations and the invasion pathways used by the species. Besides, some native populations are threatened, requiring conservation actions. Here, we describe current patterns of genetic variability of native and non-native S. glanis populations across Europe. Using microsatellite markers, we first assessed genetic variation within and between native and non-native populations. Second, we performed genetic clustering analyses to determine the genetic structure of multiple catfish populations across Europe and highlight their potential links. We revealed that native populations are more genetically diverse than non-native populations, and highlight complex introduction pathways involving several independent sources of introduction, which likely explain the invasion success of this large predatory fish across western Europe.Impacts of environmental conditions and management of sluice gates on glass eel migration
de Colin Bouchard, Olivier Boutron, Jordane Labremon, Hilaire Drouineau, Patrick Lambert, Delphine Nicolas
In Estuarine, Coastal and Shelf Science, Online (November, 2022), 108139
En ligne : www.sciencedirect.com[...]
Anthropogenic barriers such as tidal gates impair animal migration and ecological continuity. For migratory fishes, barriers may alter or impeach both upstream and downstream migrations. Juveniles of European eels, namely glass eels, have to pass those barriers when migrating upstream, whereas they have limited swimming capacities and are dependent on several environmental variables. Hydrological conditions, which can be modified by barrier management, are critical for glass eels. Here, we investigated the links between hydrological conditions and barrier management and the recruitment of glass eels at a connection between the Mediterranean Sea and a lagoon. To do that, we modeled the recruitment of glass eels over ten seasons accounting for temporal variations and co-variable effects. We modeled three aspects of recruitment: presence, level, and composition. We found that monthly and inter-annual effects explained the main part of the variations in glass eel recruitment but accounting for environmental effects improved our models, with a positive effect of temperature, for instance. We associated low levels of catches and recruitment of rather old individuals to high water flow rates when water flows out of the lagoon. Those results call for further studies on how sluice gate management may improve glass eel recruitment and seem to indicate that local stakeholders should adjust the number of open gates depending on the water level on both sides of the barrier.
de Colin Bouchard, Hilaire Drouineau, Patrick Lambert, Olivier Boutron, Delphine Nicolas
In ICES Journal of Marine Science, 79(6) (August, 2022), 1874-1887
En ligne : doi.org[...]
Understanding spatio-temporal dynamics of glass eel recruitment is necessary to characterize eel population status and the stock of future elvers. Despite numerous studies that have characterized recruitment across Europe, multiple systems along the Mediterranean coasts need a deeper look. We built a Bayesian State-Space Model to investigate the temporal variations in glass eel recruitment in the Rhône delta (France). The model was suited to address the spatial heterogeneity due to the complexity of this system constituted by numerous entrance pathways. Over 13 years, we found inter-annual variations without a particular trend. Here, an overall migration peak occurred in February–March for the system, but substantial spatial variations in the resulting recruitment were visible. Spatial variations in the inter-annual dynamics and migration peak pointed out the necessity to account for spatial heterogeneity in the dynamics of glass eel recruitment. The highlighted inter-annual variations are consistent with analysis of coincident time-series in other sites in Europe (e.g. WGEEL), and the migration peak’s timing is similar to peaks observed in other estuaries. Spatial variations in the migration peak suggest a potential effect of local environment conditions on the recruitment. Our model provided a suitable approach to investigate temporal variations while accounting for spatial heterogeneity.Cancer Susceptibility as a Cost of Reproduction and Contributor to Life History Evolution
de Antoine M. Dujon, Justine Boutry, Sophie Tissot, Jean-François Lemaître, Amy M. Boddy, Anne-Lise Gérard, Alexandra Alvergne, Audrey Arnal, Orsolya Vincze, Delphine Nicolas, et al.
In Frontiers in Ecology and Evolution, Online (May, 2022), 18
En ligne : www.frontiersin.org[...]
Reproduction is one of the most energetically demanding life-history stages. As a result, breeding individuals often experience trade-offs, where energy is diverted away from maintenance (cell repair, immune function) toward reproduction. While it is increasingly acknowledged that oncogenic processes are omnipresent, evolving and opportunistic entities in the bodies of metazoans, the associations among reproductive activities, energy expenditure, and the dynamics of malignant cells have rarely been studied. Here, we review the diverse ways in which age-specific reproductive performance (e.g., reproductive aging patterns) and cancer risks throughout the life course may be linked via trade-offs or other mechanisms, as well as discuss situations where trade-offs may not exist. We argue that the interactions between host–oncogenic processes should play a significant role in life-history theory, and suggest some avenues for future research.
de Anastasios Bounas, Giorgos Catsadorakis, Irene Koutseri, Harris Nikolaou, Delphine Nicolas, Myrsini Malakou, Alain Jean Crivelli
In Knowledge and Management of Aquatic Ecosystems, 422 (2021), 28
En ligne : www.kmae-journal.org[...]
Freshwater fish declines are triggered by a suite of anthropogenic threats, including habitat degradation, climate and land use change, biological invasions, pollution and overfishing. Robust monitoring schemes are needed to understand and detect any effects of different factors on freshwater fish abundance and to be able to predict and respond to potential stressors. Here, we used standardized biomass-per-unit-effort (BPUE) data deriving from gillnet sampling over a 34-year period in the two Prespa Lakes and determined species trends using general additive models coupled with structural change models. Furthermore, the influence of seven environmental variables was assessed for each fish species using an analytical approach based on random forests. We showed that the total annual BPUE is increasing in Lake Mikri Prespa whereas it is stable in Megali Prespa and that the relative BPUE of introduced species in the former is increasing through the years. Differences in the lakes' trophic status were reflected in species trend patterns. Random forests showed that air temperature, the introduction of the invasive Lepomis gibbosus, predation and water management played a role in shaping species biomass in Mikri Prespa whereas abiotic factors are the main drivers of biomass changes in Megali Prespa. Our results provide empirical evidence on the importance of long-term monitoring in distinguishing between direct and indirect effects of large-scale stressors on fish abundance as well as insights towards sustaining the integrity of fish communities.
de Guillaume Marchessaux, Delphine Nicolas, Alain Jean Crivelli, Silke Befeld, Pascal Contournet, Delphine Thibault
In BioInvasions Records, 9(3) (2020), 471-481
En ligne : www.reabic.net[...]
The introduced ctenophore Mnemiopsis leidyi A. Agassiz, 1865 was observed in the Vaccarès Lagoon (River Rhône delta, southeast France) for the first time in 2016. Large blooms had been observed during the summer in 2016, with monthly zooplankton community monitoring carried out from November 2016 to October 2017. This was done to better understand the dynamics of this ctenophore within this brackish Lagoon. In parallel, we report the first record of Mnemiopsis leidyi in another Mediterranean lagoon near Camargue delta (Estomac Lagoon) in 2019.
de Khalid Rind, Quentin Rodriguez‐Barucg, Delphine Nicolas, Patricia Cucchi, Jehan-Hervé Lignot
In Journal of Fish Biology, On line (12/03/2020), 13
En ligne : onlinelibrary.wiley.com[...]
Three-spined sticklebacks (Gasterosteus aculeatus L.) living at the southern limit of the species distribution range could possess specific morphological and physiological traits that enable these fish to live at the threshold of their physiological capacities. Morphological analysis was carried out on samples of sticklebacks living in different saline habitats of the Camargue area (Rhone delta, northern Mediterranean coast) obtained from 1993 to 2017. Salinity acclimation capacities were also investigated using individuals from freshwater-low salinity drainage canals and from mesohaline–euryhaline lagoons. Fish were maintained in laboratory conditions at salinity values close to those of their respective habitats: low salinity (LS, 5‰) or seawater (SW, 30‰). Fish obtained from a mesohaline brackish water lagoon (BW, 15‰) were acclimated to SW or LS. Oxygen consumption rates and branchial Na+/K+-ATPase (NKA) activity (indicator of fish osmoregulatory capacity) were measured in these LS or SW control fish and in individuals subjected to abrupt SW or LS transfers. At all the studied locations, only the low-plated “leiurus” morphotype showed no spatial or temporal variations in their body morphology. Gill rakers were only longer and denser in fish sampled from the LS–freshwater (FW) drainage canals. All fish presented similar physiological capacities. Oxygen consumption rates were not influenced by salinity challenge except in SW fish transferred to LS immediately and 1 h after transfer. However, and as expected, gill NKA activity was salinity dependent. Sticklebacks of the Camargue area sampled from habitats with contrasted saline conditions are homogenously euryhaline, have low oxygen consumption rates and do not appear to experience significantly greater metabolic costs when challenged with salinity. However, an observed difference in gill raker length and density is most probably related to the nutritional condition of their habitat, indicating that individuals can rapidly acclimatize to different diets.Estimating biodiversity changes in the Camargue wetlands: An expert knowledge approach
de Sara Fraixedas, Thomas Galewski, Sofia Ribeiro-Lopes, Jonathan Loh, Jacques Blondel, Hugo Fontes, Patrick Grillas, Philippe Lambret, Delphine Nicolas, Anthony Olivier, et al.
In PLOS ONE, 14(10) (24 oct. 2019), e0224235
En ligne : journals.plos.org[...]
Mediterranean wetlands are critical strongholds for biodiversity and the provision of ecosystem functions and services; yet, they are being severely degraded by a number of socio-economic drivers and pressures, including climate change. Moreover, we still lack comprehensive understanding of the extent to which biodiversity loss in Mediterranean wetlands will accelerate change in ecosystem processes. Here, we evaluate how changes in biodiversity can alter the ecosystem of the Camargue (southern France). We collected data on species presence/absence, trends and abundance over a 40-year period by combining observations from the scholarly literature with insights derived from expert knowledge. In total, we gathered more than 1500 estimates of presence/absence, over 1400 estimates of species abundance, and about 1400 estimates of species trends for eight taxonomic groups, i.e. amphibians, reptiles, breeding birds, fish, mammals, dragonflies (odonates), orthopterans and vascular plants. Furthermore, we used information on recently arrived species and invasive species to identify compositional changes across multiple taxa. Complementing targeted literature searches with expert knowledge allowed filling important gaps regarding the status and trends of biodiversity in the Camargue. Species trend data revealed sharp population declines in amphibians, odonates and orthopterans, while birds and plants experienced an average increase in abundance between the 1970s and the 2010s. The general increasing trends of novel and invasive species is suggested as an explanation for the changing abundance of birds and plants. While the observed declines in certain taxa reflect the relative failure of the protection measures established in the Camargue, the increasing exposure to novel and invasive species reveal major changes in the community structure of the different taxonomic groups. This study is the first attempt to assess changes in biodiversity in the Camargue using an expert knowledge approach, and can help manage the uncertainties and complexities associated with rapid social-ecological change in other Mediterranean wetlands.
de C. Musseau, S. Vincenzi, D. Jesensek, S. Boulêtreau, F. Santoul, Delphine Nicolas, Alain Jean Crivelli
In Ecology of Freshwater Fish, 27(3) (2018)
The non-native rainbow trout (Oncorhynchus mykiss) has been introduced worldwide for angling purposes and has established self-reproducing populations in many parts of the world. Introduced rainbow trout often have negative effects on the native salmonid species, ranging from decrease abundance, growth, and survival, to their local extinction. Assessing the effects of introduced rainbow trout on the native species is thus crucial to better set up conservation programs. In this study, we investigated the effects of non-native rainbow trout on the diet of native marble trout (Salmo marmoratus) living in the Idrijca River (Slovenia). An impassable waterfall separates the stream in two sectors only a few hundred meters apart: a downstream sector (treatment) in which marble trout live in sympatry (MTs) with rainbow trout (RTs) and an upstream sector (control) in which marble trout live in allopatry (MTa). Specifically, we investigated using stable isotopes the effects of rainbow trout on dietary niche, diet composition, body condition, and lipid content of marble trout. We found dietary niche expansion and niche shift in marble trout living in sympatry with rainbow trout. Compared to MTa, MTs had higher piscivory rate and showed higher body condition and pre-reproduction lipid content. Our results indicate that the presence of rainbow trout did not have negative effects on marble trout diet and condition and that changes in dietary niche of marble trout are likely to be an adaptive response to the presence of rainbow trout and further research is needed to better understand.Physico-chemical thresholds in the distribution of fish species among French lakes
de Vincent Roubeix, Martin Daufresne, Christine Argillier, Julien Dublon, Anthony Maire, Delphine Nicolas, Jean-Claude Raymond, Pierre-Alain Danis
In Knowledge and Management of Aquatic Ecosystems, 418 (2017), 14
En ligne : www.kmae-journal.org[...]
The management of lakes requires the definition of physico-chemical thresholds to be used for ecosystem preservation or restoration. According to the European Water Framework Directive, the limits between physico-chemical quality classes must be set consistently with biological quality elements. One way to do this consists in analyzing the response of aquatic communities to environmental gradients across monitoring sites and in identifying ecological community thresholds, i.e. zones in the gradients where the species turnover is the highest. In this study, fish data from 196 lakes in France were considered to derive ecological thresholds using the multivariate method of gradient forest. The analysis was performed on 25 species and 36 environmental parameters. The results revealed the highest importance of maximal water temperature in the distribution of fish species. Other important parameters included geographical factors, dissolved organic carbon concentration and water transparency, while nutrients appeared to have low influence. In spite of the diversity of species responses to the gradients, community thresholds were detected in the gradients of the most important physico-chemical parameters and of total phosphorus and nitrate concentrations as well. The thresholds identified in such macroecological study may highlight new patterns of species natural distribution and improve niche characterization. Moreover, when factors that may be influenced by human activities are involved, the thresholds could be used to set environmental standards for lake preservation. / La gestion des plans d'eau nécessite la définition de seuils physico-chimiques pour la préservation ou la restauration des écosystèmes. Selon la Directive Cadre européenne sur l'Eau, les limites de classes de qualité physico-chimiques doivent être fixées en cohérence avec les éléments de qualité biologique. Une façon de faire consiste à analyser les réponses des communautés aquatiques aux gradients environnementaux formés par les sites de monitoring et d'identifier des seuils écologiques de communautés, c'est-à-dire des zones dans les gradients où le turnover des espèces est le plus important. Dans cette étude, les données de pêches provenant de 196 plans d'eau ont été considérées pour rechercher des seuils écologiques avec la méthode de gradient forest. L'analyse a porté sur 25 espèces avec 36 paramètres environnementaux. Les résultats ont révélé que la température maximale était le facteur le plus important dans la distribution des espèces de poissons. Les autres paramètres importants étaient les facteurs géographiques, la concentration en carbone organique dissous et la transparence de l'eau alors que les nutriments semblaient avoir peu d'influence. Malgré la diversité de réponses des espèces aux gradients, des seuils de communautés ont été détectés dans les gradients des paramètres physico-chimiques les plus importants ainsi que dans ceux des concentrations en phosphore total et en nitrates. Les seuils identifiés dans une telle étude macroécologique peuvent faire apparaître de nouveaux patrons de distribution naturelle des poissons et améliorer la caractérisation des niches spécifiques. De plus, quand des facteurs influencés par les activités humaines sont impliqués, ces seuils pourraient être utilisés pour fixer des limites pour la protection des plans d'eau.
