Centre de Recherche sur la Biodiversité et l'Environnement

The world‘s biodiversity is currently in rapid decline - Europe being no exception - with as principal cause a human-mediated global change. The Natura 2000 network is an important conservation tool for European biodiversity; it is a network of natural and semi-natural sites within Europe with high heritage values due to the exceptional flora and fauna they contain. Here, we evaluated the coverage of 300 threatened species by the Natura 2000 network, and determined potential factors influencing the designation of sites and the structure of the network within a country (social, ecological and demographic national factors). Our analysis was based on a coverage ratio between the Natura 2000 sites and distribution maps of threatened European species. We showed that the distributions of a large proportion of threatened species of mammals, birds and reptiles considered in our study were highly covered (above 90%) by the current Natura 2000 network, demonstrating that the Natura 2000 network also covers species not listed in the annexes of the Nature Directives. However, our results confirm that a large proportion of threatened species (some of them listed on the European annexes), especially fishes, are currently poorly covered by the Natura 2000 network. The coverage of species likely seemed to be highly related to national demographic factors, i.e. the proportion of the national urban population. Our analysis also suggested that the designation of sites depends too strongly on governmental politics, economic and cultural criteria, and interactions between society and the environment. A more effective process might be necessary to ensure the Natura 2000 network reaches its potential as the most important and comprehensive network of protected areas intended to halt the loss of biodiversity in Europe in the near future.

ABSTRACT Aim The urgency for remote, reliable and scalable biodiversity monitoring amidst mounting human pressures on ecosystems has sparked worldwide interest in Passive Acoustic Monitoring (PAM), which can track life underwater and on land. However, we lack a unified methodology to report this sampling effort and a comprehensive overview of PAM coverage to gauge its potential as a global research and monitoring tool. To address this gap, we created the Worldwide Soundscapes project, a collaborative network and growing database comprising metadata from 416 datasets across all realms (terrestrial, marine, freshwater and subterranean). Location Worldwide, 12,343 sites, all ecosystem types. Time Period 1991 to present. Major Taxa Studied All soniferous taxa. Methods We synthesise sampling coverage across spatial, temporal and ecological scales using metadata describing sampling locations, deployment schedules, focal taxa and audio recording parameters. We explore global trends in biological, anthropogenic and geophysical sounds based on 168 selected recordings from 12 ecosystems across all realms. Results Terrestrial sampling is spatially denser (46 sites per million square kilometre—Mkm 2 ) than aquatic sampling (0.3 and 1.8 sites/Mkm 2 in oceans and fresh water) with only two subterranean datasets. Although diel and lunar cycles are well sampled across realms, only marine datasets (55%) comprehensively sample all seasons. Across the 12 ecosystems selected for exploring global acoustic trends, biological sounds showed contrasting diel patterns across ecosystems, declined with distance from the Equator, and were negatively correlated with anthropogenic sounds. Main Conclusions PAM can inform macroecological studies as well as global conservation and phenology syntheses, but representation can be improved by expanding terrestrial taxonomic scope, sampling coverage in the high seas and subterranean ecosystems, and spatio‐temporal replication in freshwater habitats. Overall, this worldwide PAM network holds promise to support cross‐realm biodiversity research and monitoring efforts.

New Caledonia represents an extraordinary ‘laboratory’ for evolutionary biologists. It harbours a high level of species richness and endemism as well as numerous relict groups. Here, I briefly review the various hypotheses that have been proposed to explain New Caledonian biodiversity and discuss the use of the phylogenetic method to test these hypotheses. New Caledonia has long been depicted as a museum of biodiversity, where the ‘long isolation of the territory’ and its ‘climatic stability’ can explain the presence of supposedly old endemic relicts, as well as the high species richness and endemism. This classical view has been accepted by many biologists and journalists for decades, despite contradicting geological evidence that New Caledonia underwent complete submersion. For example, in the latest geological review on New Caledonia (written by a geologist working on-site), the conclusion of submersion is unambiguous: after the Cretaceous the Norfolk Ridge/New Caledonia Ridge was below sea level up to the Late Eocene (or possibly up to the Middle Eocene) [...] one may infer that the Gondwanian fauna and flora were introduced in New Caledonia during or after the Middle to Late Eocene. Other recent geological papers also refer to such submersion until c. 35 Ma (Schellart, 2007, figure 4 and Collot et al., 2008, figure 15). In addition, all of the regional boreholes (DSDP 206 – New Caledonian basin; DSDP 207 and 208 – Lord Howe Rise) indicate that the region east of the Norfolk Ridge was below sea level until the Late Palaeocene (Collot et al., 2008). In this context, the Late Cretaceous to Early Eocene, mostly non-marine, siliciclastic rocks of the Kenn Plateau highlighted by Ladiges & Cantrill (2007) are of no particular interest since this structure is located East of Lord Howe Rise. Interestingly, despite the dominance of the museum hypothesis in the literature, biologists have long acknowledged a general submergence of the territory after its break-up from the eastern margin of Gondwana. This has led to alternative hypotheses, the first of which is here called the mountain refugia hypothesis. Based solely on the presence of relict groups in the territory, it rejects the notion of a complete submersion of the island despite the lack of geological evidence: ‘In spite of geological arguments, these submersions can never have been complete, since floral distributions indicate that considerable surface must have remained above water and served as refuges’ (Morat et al., 1984, p. 84). In a similar paper, Morat et al. (1986) propose an alternative hypothesis, here called the island refugia hypothesis. This hypothesis states that close ephemeral islands may have existed and served as refugia for the old Gondwanan biota: ‘Land areas of varying size that may be supposed to have existed near New Caledonia even during periods of general submergence would provide refuges and stepping-stones for the vegetation’ (Morat et al., 1986, p. 645). This hypothesis has never been clearly attested by geological evidence, which would require the finding of organic debris in sediments of the same age as the submersion (B. Pelletier, personal communication). However, it is possible: If New Caledonia was not a refuge for the Gondwanian biodiversity, did other land – except Australia – exist in the region before the Middle–Late Eocene? [...] This provides the possibility for the building of an alignment of islands likely restricted in size east of the Norfolk–New Caledonia Ridge [...] Finally, the long-distance dispersal hypothesis suggests that the present New Caledonian biota reached the island from neighbouring regions (Pole, 1994). This hypothesis implies that for endemic relict groups, the source population went extinct in the territory of origination after the colonization of New Caledonia. In this context, phylogenetic methodology and molecular dating provide the necessary framework with which to study the origin of biodiversity in the region. It is worthwhile to remind ourselves of the difference between the origin and diversification of a group. The most recent common ancestor of a given group and its sister-group represents the origin, and the most recent common ancestor of all the representatives of a given group represents the diversification. If New Caledonian biodiversity follows the museum hypothesis (Fig. 1, A), we would expect both the origin and the diversification of groups to be old, dating back to the fragmentation of Gondwana around 80 Ma. If the diversification of groups is younger than their origin (Fig. 1, B), as for some invertebrates (e.g. Boyer et al., 2007), vertebrates (e.g. Bauer et al., 2006) and plants (e.g. Setoguchi et al., 1998), it is practically impossible to distinguish between the three alternative hypotheses (mountain refugia, island refugia and long-distance dispersal). Some authors have favoured one or other of the alternative hypotheses. Pole (1994) favoured a post-Eocene dispersal hypothesis; Jolivet & Verma (2008) favoured an explanation implying incomplete submersion; and Heads (2008) favoured an island refugia hypothesis. None of those authors based their argumentation on a phylogenetic methodology. Indeed, as shown in Fig. 1, B, the same phylogenetic pattern (old origin and recent diversification) can be explained by the three hypotheses. Favouring one hypothesis over another is an expression of personal opinion based on geological arguments. In the case of a demonstrated recent origin (more recent that 80 Ma), the only valid interpretation that remains is long-distance dispersal (Fig. 1, C). Alternative phylogenetic patterns over time and their possible interpretation. OG, outgroup; NC, New Caledonian. NC endemics are assumed to represent endemic monophyletic groups with their sister-group (OG) distributed outside New Caledonia. There is an increasing body of evidence showing that much of the New Caledonian diversifications do not date back to the fragmentation of Gondwana (e.g. Murienne et al., 2005). This new paradigm is in agreement with the geological history of the territory indicating an emergence around the Middle–Late Eocene. Even if phylogenetics were to prove to be useful to study the causes of diversification in New Caledonia, or to test if supposedly Gondwanan groups follow a museum model, alternative hypotheses (mountain refugia, island refugia, long-distance dispersal) about the presence of relict groups all explain the same phylogenetic pattern, and so the hypotheses cannot be separated on the evidence. In this context, the presence of numerous relict groups in New Caledonia remains puzzling. Editor: John Lambshead

Global biodiversity is under accelerating threats, and species are succumbing to extinction before being described. Madagascar's biota represents an extreme example of this scenario, with the added complication that much of its endemic biodiversity is cryptic. Here we illustrate best practices for clarifying cryptic diversification processes by presenting an integrative framework that leverages multiple lines of evidence and taxon-informed cut-offs for species delimitation, while placing special emphasis on identifying patterns of isolation by distance. We systematically apply this framework to an entire taxonomically controversial primate clade, the mouse lemurs (genus Microcebus, family Cheirogaleidae). We demonstrate that species diversity has been overestimated primarily due to the interpretation of geographic variation as speciation, potentially biasing inference of the underlying processes of evolutionary diversification. Following a revised classification, we find that crypsis within the genus is best explained by a model of morphological stasis imposed by stabilizing selection and a neutral process of niche diversification. Finally, by clarifying species limits and defining evolutionarily significant units, we provide new conservation priorities, bridging fundamental and applied objectives in a generalizable framework.

In comparative biology, character observations initially separate similar and dissimilar characters. Only similar characters are considered for phylogeny reconstruction; their homology is attested in a two-step process, firstly a priori of phylogeny reconstruction by accurate similarity statements, and secondly a posteriori of phylogeny analysis by congruence with other characters. Any pattern of non-homology is then a homoplasy, commonly, but vaguely, associated with "convergence". In this logical scheme, there is no way to analyze characters which look similar, but cannot meet usual criteria for homology statements, i.e., false similarity detected a priori of phylogenetic analysis, even though such characters may represent evolutionarily significant patterns of character transformations. Because phylogenies are not only patterns of taxa relationships but also references for evolutionary studies, we propose to redefine the traditional concepts of parallelism and convergence to associate patterns of non-homology with explicit theoretical contexts: homoplasy is restricted to non-similarity detected a posteriori of phylogeny analysis and related to parallelism; non-similarity detected a priori of phylogenetic analysis and necessarily described by different characters would then correspond to a convergence event s. str. We propose to characterize these characters as heterologous (heterology). Heterology and homoplasy correspond to different non-similarity patterns and processes; they are also associated with different patterns of taxa relationships: homoplasy can occur only in non-sister group taxa; no such limit exists for heterology. The usefulness of these terms and concepts is illustrated with patterns of acoustic evolution in ensiferan insects.

The influential concept of the rare biosphere in microbial ecology has underscored the importance of taxa occurring at low abundances yet potentially playing key roles in communities and ecosystems. Here, we refocus the concept of rare biosphere through a functional trait-based lens and provide a framework to characterize microbial functional rarity, a combination of numerical scarcity across space or time and trait distinctiveness. We demonstrate how this novel interpretation of the rare biosphere, rooted in microbial functions, can enhance our mechanistic understanding of microbial community structure. It also sheds light on functionally distinct microbes, directing conservation efforts towards taxa harboring rare yet ecologically crucial functions.

Abstract Aim Combining different biodiversity dimensions can reveal new diversity patterns disclosing the relative roles of historical, environmental and anthropogenic factors in shaping global seed plant diversity. Location Global. Time period Present. Major taxa studied Vascular plants. Methods We collated a database encompassing taxonomic (249,000 species), functional and phylogenetic information (34,694 species) of seed plants across different regions of the world. Species richness in each region was weighted accounting for their phylogenetic and functional distinctiveness, obtaining a new metric—μ‐diversity—which was modelled to disentangle the relative roles of historical factors such as climate variability since the Last Glacial Maximum (LGM), environmental features (e.g. actual evapotranspiration—AET) and anthropogenic factors (past and current). Results Higher μ‐diversity was observed in Papuasia, South East Asia, Australia and Central America, whereas the lowest values were primarily located in the Northern Hemisphere. Climate variability and AET were the most important determinants of μ‐diversity and individual diversity facets, whereas the importance of past human impacts (i.e. the onset of pastoralism) equated or exceeded those of the present ones. Main conclusions Our integrative approach proved more sensitive in describing species diversity patterns. Few areas on Earth host high and unique proportions of multiple diversity facets and individual diversity facets contribute differently to μ‐diversity across continents. Historical climate stability and water‐energy dynamics strongly affect species diversity, but we also observed that past land‐use legacy may have influenced current plant diversity, which is under intense anthropogenic pressure, especially in Asia as well as in Central and South America.

Coccinellids were sampled in 88 citrus groves from the centre / south of continental Portugal. Analysis of distribution were performed by the usual indices but also with the help of a new method - SADIE. 38 species were identified, 36 of which are predators. Five coccinellids seem to have aggregated distributions ; UTM maps of those species distributions are presented. Among these five, Nephus reunioni Fürsch and Nephus includens (Kirsch) are the more abundant. Previous studies about these two coccinellids distributions are confirmed: N. reunioni is limited to a region of about 80 Km diameter around Lisbon while N. includens appears only in Algarve. Coccidophagous species and a group of Scymnus sp. and Nephus sp., with unknown food preferences in citrus, are the most important in terms of richness and abundance.

A character of special interest in evolutionary studies is usually optimized on a phylogenetic tree, with or without the outgroups employed in that analysis. Both practices are never justified and look like arbitrary choices. Focusing on one example, we draw the conclusion that authors retain or remove outgroups depending on the way these outgroups sample the diversity of states of the character(s) of special interest. The topology without outgroups is often used by authors when different outgroup taxa non-exhaustively sample the different states of the character of interest outside of the ingroup. This can make the analysis incoherent, because its different steps are not based on the same data matrix (outgroups are removed in the last step). It can provide several incoherent and possibly different patterns for a same character of interest, one issuing from the first step of phylogeny construction and the other resulting from the a posteriori optimization on the truncated topology. Phylogenetic analyses should be designed to minimize this problem, selecting outgroup and ingroup taxa whose diversity of character states is needed for reconstructing the evolutionary history of the character of interest.

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Acoustic communication plays a prominent role in various ecological and evolutionary processes involving social interactions. The properties of acoustic signals are thought to be influenced not only by the interaction between signaller and receiver but also by the acoustic characteristics of the environment through which the signal is transmitted. This conjecture forms the core of the so-called "acoustic adaptation hypothesis" (AAH), which posits that vegetation structure affects frequency and temporal parameters of acoustic signals emitted by a signaller as a function of their acoustic degradation properties. Specifically, animals in densely vegetated "closed habitats" are expected to produce longer acoustic signals with lower repetition rates and lower frequencies (minimum, mean, maximum, and peak) compared to those inhabiting less-vegetated "open habitats". To date, this hypothesis has received mixed results, with the level of support depending on the taxonomic group and the methodology used. We conducted a systematic literature search of empirical studies testing for an effect of vegetation structure on acoustic signalling and assessed the generality of the AAH using a meta-analytic approach based on 371 effect sizes from 75 studies and 57 taxa encompassing birds, mammals and amphibians. Overall, our results do not provide consistent support for the AAH, neither in within-species comparisons (suggesting no overall phenotypically plastic response of acoustic signalling to vegetation structure) nor in among-species comparisons (suggesting no overall evolutionary response). However, when considering birds only, we found weak support for the AAH in within-species comparisons, which was mainly driven by studies that measured frequency bandwidth, suggesting that this variable may exhibit a phenotypically plastic response to vegetation structure. For among-species comparisons in birds, we also found support for the AAH, but this effect was not significant after excluding comparative studies that did not account for phylogenetic non-independence. Collectively, our synthesis does not support a universal role of vegetation structure in the evolution of acoustic communication. We highlight the need for more empirical work on currently under-studied taxa such as amphibians, mammals, and insects. Furthermore, we propose a framework for future research on the AAH. We specifically advocate for a more detailed and quantitative characterisation of habitats to identify frequencies with the highest detection probability and to determine if frequencies with greater detection distances are preferentially used. Finally, we stress that empirical tests of the AAH should focus on signals that are selected for increased transmission distance.

Blattoidea are comprised of the major lineages Blattidae, Lamproblattidae, Tryonicidae, Anaplectidae, and Cryptocercidae + Isoptera. Despite a number of studies, no consensus exists regarding the relationships between these lineages. Additionally, the current division of Blattidae into Archiblattinae, Blattinae, Macrocercinae and Polyzosteriinae needs phylogenetic testing. We present a molecular phylogeny of Blattoidea recovering all the major lineages as monophyletic with Lamproblattidae as sister to the remaining Blattoidea and Tryonicidae as sister to Cryptocercidae + Isoptera. Contrary to many previous studies, we found a high degree of consistency between analyses, possibly due to improved taxon sampling. We found that none of the currently accepted subfamilies of Blattidae are monophyletic. Mapping of distribution revealed a clear geographic structuring at odds with the current subfamilial classification. Based on results from this and other studies, we present a revised classification of Blattidae: we erect two new subfamilies, Eurycotiinae stat. rev. and Austrostylopyginae subfam. nov. , reinstate Duchailluiinae stat. rev. and subsume Macrocercinae in Polyzosteriinae. We also present a division of Polyzosteriinae into tribes: Polyzosteriini, Methanini stat. rev. , Rothisilphini trib. nov. , and Celatoblattini trib. nov. Within Blattidae, Duchailluiinae is sister to the remaining taxa, while Austrostylopyginae is most likely sister to all other Blattidae except Duchailluiinae.

Rivers have an intricate relationship with the vegetation that colonizes them. Riparian plants, capable of thriving within river corridors, both respond to and influence geomorphology. Yet interactions between river morphodynamics and vegetation tend to be context specific, making it challenging to generalize findings between locations. The current comprehension of vegetation interaction with physical processes, and especially its effects on river morphodynamics, still lacks clarity. This article examines numerous sources of variation in plant responses to, and effects on, river morphodynamics. Vegetation influences on geomorphological parameters vary in terms of intensity and spatial extent along the gradient of river energy and according to the fluvial style. Whilst feedbacks between vegetation and river morphodynamics are readily discernible at a local scale, on larger spatial scales, it can remain difficult to precisely determine cause-and-effect relationships that link hydrogeomorphic and vegetation drivers and the outcomes of their feedbacks. This is especially problematic for those feedbacks that give rise to emergent system landscape behaviour in meandering and island braided rivers. By contrast, in certain river configurations, such as anabranching rivers, the imprint of vegetation on the riverscape can be clearly evident. The imprint of vegetation is also supported by evidence from the ancient alluvial record. Through this review, we highlight key perspectives from a wide range of modern and ancient rivers of varied configuration in order to inform future studies of vegetation responses to, and effects on, river morphodynamics.

Abstract The good functioning of aquatic ecosystems is essential for providing diverse ecosystem services that benefit humans. The degradation of ecosystem health due to continuous stressors, such as climate change or water pollution, is leading to an increase in human health risks and well-being. Indicators have been developed to determine human health risks from recreational and drinking water. Still, a general application to aquatic ecosystems linking ecosystem health and human health risks has not been done. We here reviewed indicators and indices applied to assess the health of aquatic ecosystems and their links with human health risk and well-being. We evaluated the extent to which indicators can witness a risk to human health and well-being. A total of 245 articles were reviewed, consisting of 185 on the assessment of aquatic ecosystem health and 60 linking ecosystem health and human health or well-being. Out of the 65 indices described, we evaluated the use of several parameters and their relevance to evaluate human health risks, including physico-chemical parameters, bioindicators, contaminants, and pathogens, therefore covering the various sources of ecosystem disturbance. Based on our assessment, we propose a set of indicators that would allow for the inclusion of risks for human health and well-being in the assessment of ecosystem health (e.g. coliforms, algae, pH, nutrients, chemical compounds, and ecosystem services). Measuring these parameters should be incorporated into future studies to allow an understanding of the linkage of ecosystem and human health.

The increase in Earth observations from space in recent years supports improved quantification of carbon storage by terrestrial vegetation and fosters studies that relate satellite measurements to biomass retrieval algorithms. However, satellite observations are only indirectly related to the carbon stored by vegetation. While ground surveys provide biomass stock measurements to act as reference for training the models, they are sparsely distributed. Here, we addressed this problem by designing an algorithm that harnesses the interplay of satellite observations, modeling frameworks and field measurements, and generated global estimates of above-ground biomass (AGB) density that meet the requirements of the scientific community in terms of accuracy, spatial and temporal resolution. The design was adapted to the amount, type and spatial distribution of satellite data available around the year 2020. The retrieval algorithm estimated AGB annually by merging estimates derived from C- and L-band Synthetic Aperture Radar (SAR) backscatter observations with a Water Cloud type of model and does not rely on AGB reference data at the same spatial scale as the SAR data. This model is integrated with functions relating to forest structural variables that were trained on spaceborne LiDAR observations and sub-national AGB statistics. The yearly estimates of AGB were successively harmonized using a cost function that minimizes spurious fluctuations arising from the moderate-to-weak sensitivity of the SAR backscatter to AGB. The spatial distribution of the AGB estimates was correctly reproduced when the retrieval model was correctly set. Over-predictions occasionally occurred in the low AGB range (<50 Mg ha−1) and under-predictions in the high AGB range (>300 Mg ha−1). These errors were a consequence of sometimes too strong generalizations made within the modeling framework to allow reliable retrieval worldwide at the expense of accuracy. The precision of the estimates was mostly between 30% and 80% relative to the estimated value. While the framework is well founded, it could be improved by incorporating additional satellite observations that capture structural properties of vegetation (e.g., from SAR interferometry, low-frequency SAR, or high-resolution observations), a dense network of regularly monitored high-quality forest biomass reference sites, and spatially more detailed characterization of all model parameters estimates to better reflect regional differences.

Reconstructing the evolutionary history of great apes is of particular importance for our understanding of the demographic history of humans. The reason for this is that modern humans and their hominin ancestors evolved in Africa and thus shared the continent with the ancestors of chimpanzees and gorillas. Common chimpanzees (Pan troglodytes) are our closest relatives with bonobos (Pan paniscus) and most of what we know about their evolutionary history comes from genetic and genomic studies. Most evolutionary studies of common chimpanzees have assumed that the four currently recognised subspecies can be modelled using simple tree models where each subspecies is panmictic and represented by one branch of the evolutionary tree. However, several studies have identified the existence of significant population structure, both within and between subspecies, with evidence of isolation-by-distance (IBD) patterns. This suggests that demographic models integrating population structure may be necessary to improve 1 our understanding of their evolutionary history. Here we propose to use n-island models within each subspecies to infer a demographic history integrating population structure and changes in connectivity (i.e. gene flow). For each subspecies, we use SNIF (structured non-stationary inference framework), a method developed to infer a piecewise stationary n-island model using PSMC (pairwise sequentially Markovian coalescent) curves as summary statistics. We then propose a general model integrating the four subspecies metapopulations within a phylogenetic tree. We find that this model correctly predicts estimates of within subspecies genetic diversity and differentiation, but overestimates genetic differentiation between subspecies as a consequence of the tree structure. We argue that spatial models integrating gene flow between subspecies should improve the prediction of between subspecies differentiation and IBD patterns. We also use a simple spatially structured model for bonobos and chimpanzees (without admixture) and find that it explains signals of admixture between the two species that have been reported and could thus be spurious. This may have implications for our understanding of the evolutionary history of the Homo genus.

Understanding ecosystem responses to global change have long challenged scientists due to notoriously complex properties arising from the interplay between biological and environmental factors. We propose the concept of ecosystem synchrony - that is, similarity in the temporal fluctuations of an ecosystem function between multiple ecosystems - to overcome this challenge. Ecosystem synchrony can manifest due to spatially correlated environmental fluctuations (Moran effect), exchange of energy, nutrients, and organic matter and similarity in biotic characteristics across ecosystems. By taking advantage of long-term surveys, remote sensing and the increased use of high-frequency sensors to assess ecosystem functions, ecosystem synchrony can foster our understanding of the coordinated ecosystem responses at unexplored spatiotemporal scales, identify emerging portfolio effects among ecosystems, and deliver signals of ecosystem perturbations.

Abstract. The magnitudes of dissolved organic carbon (DOC) exports from boreal peatlands to streams through lateral subsurface flow vary during the ice-free season. Peatland water table depth and the alternation of low and high flow in peat-draining streams are thought to drive this DOC export variability. However, calculation of the specific DOC exports from a peatland can be challenging considering the multiple potential DOC sources within the catchment. A calculation approach based on the hydrological connectivity between the peat and the stream could help to solve this issue, which is the approach used in the present research. This study took place from June 2018 to October 2019 in a boreal catchment in northeastern Canada, with 76.7 % of the catchment being covered by ombrotrophic peatland. The objectives were to (1) establish relationships between DOC exports from a headwater stream and the peatland hydrology; (2) quantify, at the catchment scale, the amount of DOC laterally exported to the draining stream; and (3) define the patterns of DOC mobilization during high-river-flow events. At the peatland headwater stream outlet, the DOC concentrations were monitored at a high frequency (hourly) using a fluorescent dissolved organic matter (fDOM) sensor, a proxy for DOC concentration. Hydrological variables, such as stream outlet discharge and peatland water table depth (WTD), were continuously monitored at hourly intervals for 2 years. Our results highlight the direct and delayed control of subsurface flow from peat to the stream and associated DOC exports. Rain events raised the peatland WTD, which increased hydrological connectivity between the peatland and the stream. This led to increased stream discharge (Q) and a delayed DOC concentration increase, typical of lateral subsurface flow. The magnitude of the WTD increase played a crucial role in influencing the quantity of DOC exported. Based on the observations that the peatland is the most important contributor to DOC exports at the catchment scale and that other DOC sources were negligible during high-flow periods, we propose a new approach to estimate the specific DOC exports attributable to the peatland by distinguishing between the surfaces used for calculation during high-flow and low-flow periods. In 2018–2019, 92.6 % of DOC was exported during flood events despite the fact that these flood events accounted for 59.1 % of the period. In 2019–2020, 93.8 % of DOC was exported during flood events, which represented 44.1 % of the period. Our analysis of individual flood events revealed three types of events and DOC mobilization patterns. The first type is characterized by high rainfall, leading to an important WTD increase that favours the connection between the peatland and the stream and leading to high DOC exports. The second is characterized by a large WTD increase succeeding a previous event that had depleted DOC available to be transferred to the stream, leading to low DOC exports. The third type corresponds to low rainfall events with an insufficient WTD increase to reconnect the peatland and the stream, leading to low DOC exports. Our results suggest that DOC exports are sensitive to hydroclimatic conditions; moreover, flood events, changes in rainfall regime, ice-free season duration, and porewater temperature may affect the exported DOC and, consequently, partially offset the net carbon sequestration potential of peatlands.

International audience

How are some individuals surviving infections while others die? The answer lies in how infected individuals invest into controlling pathogen proliferation and mitigating damage, two strategies respectively called resistance and disease tolerance. Pathogen within-host dynamics (WHD), influenced by resistance, and its connection to host survival, determined by tolerance, decide the infection outcome. To grasp these intricate effects of resistance and tolerance, we used a deterministic theoretical model where pathogens interact with the immune system of a host. The model describes the positive and negative regulation of the immune response, consider the way damage accumulate during the infection and predicts WHD. When chronic, infections stabilize at a Set-Point Pathogen Load (SPPL). Our model predicts that this situation can be transient, the SPPL being then a predictor of life span which depends on initial condition (e.g. inoculum). When stable, the SPPL is rather diagnostic of non-lethal chronic infections. In lethal infections, hosts die at a Pathogen Load Upon Death (PLUD) which is almost independent from the initial conditions. As the SPPL, the PLUD is affected by both resistance and tolerance but we demonstrate that it can be used in conjunction with mortality measurement to distinguish the effect of disease tolerance from that of resistance. We validate empirically this new approach, using Drosophila melanogaster and the pathogen Providencia rettgeri . We found that, as predicted by the model, hosts that were wounded or deficient of key antimicrobial peptides had a higher PLUD, while Catalase mutant hosts, likely to have a default in disease tolerance, had a lower PLUD.