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Postnatal glucocorticoid exposure causes long-lasting effects on competitive but not neophobic behaviors in a common songbird
No full textInternational audiencePostnatal stress can affect behavior and physiology in vertebrates, but long-term effects of early-life stress experience are not well understood, especially in wild species. Glucocorticoids, steroid hormones that mediate a suite of physiological and behavioral traits in response to a changing environment, might play an important role in programming long-term responses. We examined the effects of early-life exposure to corticosterone, the primary avian glucocorticoid, on neophobic and competitive behaviors in the house sparrow (Passer domesticus). We manipulated circulating corticosterone levels in wild, free-living nestlings, then measured behavior at the juvenile and adult stages in captivity. Birds were independently tested on their response to a novel object (i.e., neophobia) and tested in their nest group on their response to a limited food source (i.e., competitive behaviors). We had alternate predictions: (1) corticosterone-treated birds would exhibit fewer neophobic behaviors and more competitive behaviors than controls if early-life corticosterone exposure adaptively prepares animals for high-stress environments; or (2) corticosterone-treated birds would be more neophobic and less competitive compared to controls if high early-life corticosterone exposure outpaces the organism's capacity to regulate stability. Additionally, we predicted that postnatal corticosterone exposure might affect juvenile behavior more than adult behavior if responses can be modulated by individual experiences over time. We found that early-life corticosterone exposure largely did not predict neophobic behaviors in response to a novel object and environment but did predict competitive behaviors in juveniles. Corticosterone-treated juvenile males tended to be less competitive and displaced more frequently than control juvenile males, whereas corticosterone-treated juvenile females tended to be more competitive than control juvenile females; however, these patterns were no longer present by adulthood. We conclude that early-life stress might have sex-specific effects in a bird's competitive ability in their first year of life, which could impact survival in populations facing novel stressors.</div
Annual trends in mercury contamination are associated with changing trophic niches of giant petrels
No full textInternational audienceAnnual variation in prey availability can influence seabird diets and hence their exposure to pollutants, including mercury (Hg). Among seabirds, those species that scavenge carrion of marine mammals and other top predators may be especially vulnerable to accumulating high Hg concentrations. In this study, total Hg (THg) concentrations and carbon (δ13C) and nitrogen (δ15N) stable isotope values were measured in chick feathers of northern giant petrels Macronectes halli and southern giant petrels M. giganteus at Bird Island, South Georgia (2013–2020). Both species are opportunistic predator-scavengers which feed mainly on penguins and Antarctic fur seal Arctocephalus gazella carrion, and to lesser extents on marine prey and other seabirds. THg concentrations were not significantly different between northern giant petrels and southern giant petrels (means ± SDs, 2.49 ± 0.92 μg g-1 dw and 2.34 ± 0.85 μg g-1 dw, respectively), but concentrations in both species declined significantly over time, as did δ13C and δ15N values. Annual feather THg concentrations of giant petrels were positively correlated with the number of dead Antarctic fur seal pups and their mortality rate at Bird Island, but not with population sizes or breeding success of penguins. Accordingly, these results suggest a shift away from carrion (associated with the decreasing size and productivity of the Antarctic fur seal population) and towards the consumption of prey from lower trophic levels (e.g., Antarctic krill Euphausia superba), with a corresponding reduction in dietary Hg exposure. Future work should investigate the consequences of changing prey availability for diets and pollutant exposure to other marine predators within the South Georgia and Scotia Sea marine ecosystems, given the ongoing environmental changes in the region
Field measurements of wave and flow dynamics along a high-energy meso-macrotidal coast adjacent to a large estuary mouth
No full textInternational audienceThe North-Médoc coast, located to the south of the Gironde estuary, exhibits complex hydrodynamic conditions driven by high-energy incident waves and large tides, which are influenced by large-scale rocky outcrops, shoals, and tidal channels on the inner shelf. These wave- and tide-driven hydrodynamics result in rapid morphological changes, with shoreline erosion peaking locally at 5 m/year. In autumn 2022, an intensive two-week field campaign was conducted along three cross-shore transects distributed across the North-Médoc coast to, for the first time, document and analyze the hydrodynamics in this area. The campaign involved collecting measurements of waves and currents across both the inner shelf and nearshore regions, using six current profilers and 13 pressure sensors. Tides were found to predominantly modulate wave transformation and flow in both the nearshore and inner shelf regions of the North-Médoc coast. Strong alongshore currents were measured across the entire study site, increasing southward, which is linked to the overall morphology of a tidal channel. Tidal currents are flood-dominated in the northern part and ebb-dominated in the southern and central parts of the study area. Total currents and wave heights are modulated by tidal elevation, with, for example, increased wave height at the coast during higher tide levels. Nearshore waves, which undergo complex transformation across the inner shelf, such as wave refraction over shoals and rocky outcrops, also drive longshore currents in the surf zone, superimposed on the tidal current. These conditions result in a strong, net, northeastward longshore current, even during low-energy wave conditions. These observations provide new insights into the hydrodynamics of this rapidly evolving coastline and establish a comprehensive dataset that will be crucial for the development and validation of process-based and reduced-complexity models in this regio
« L’OTAN est devenue un bouc émissaire facile des échecs de la défense européenne »
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Observability inequality for the wavelet-based Galerkin method
No full textThis work is about the observation and control of the wave propagation phenomena within the framework of a wavelet based Galerkin discretization methods. Unlike conventional approaches where observability/controllability are lost as the mesh size tends to zero, we show that the total energy of solutions of the discrete modele can be estimated uniformly from partial measurements on boundary. Then, wave propagation behavior can be controlled using forcing terms on that subregion, as is often desired in engineering applications.</div
Perch proximity does not predict the probability of cuckoo parasitism in a woodland host
No full textInternational audienceObligate avian brood parasites typically impose great costs on their hosts by replacing the host's offspring with their own. Multiple theories have been put forward regarding which factors influence the probability that a host nest will be parasitized. One of these, the perch proximity hypothesis, predicts that nests that are close to trees are more likely to be parasitized, as trees provide a vantage point for the parasite to observe nest building by the host. Substantial support for this hypothesis has been found in several species of brood parasites that occur in a range of open habitats, such as reed beds, marshlands and grasslands, where vantage points are likely to be scarce. However, it is unclear whether this prediction applies to species that occupy woodland habitats. Although brood parasites may be more likely to exploit nests with suitable vantage points nearby, it is possible that a high density of vegetation might obscure the nest, thereby reducing the likelihood of parasitism. Here we used a long-term data set of superb fairy-wren, Malurus cyaneus, nests to test this hypothesis in the brood-parasitic Horsfield's bronze-cuckoo, Chalcites basalis. Contrary to the prediction of the perch proximity hypothesis, parasitism risk did not increase with closer proximity of a perch to the nest; instead, we show that the risk of parasitism may decrease as tree density increases. These results suggest that exploration of the host activity hypothesis and nest exposure hypothesis may be fruitful for future work in this system
Testing the abundant centre hypothesis in a seabird: higher energy expenditure at the wintering range centre does not reduce reproductive success
No full textInternational audienceUnderstanding variation in animal distributions is a central and challenging question in ecology that has become particularly critical in the context of global environmental changes. While distributions are often studied for resident or breeding species, species range limits are equally important for migratory species in winter when population regulation may occur due to limited resources in the non‐breeding season. A central hypothesis in several theories is that the density, fitness and performance of individuals decrease towards the edge of the range as organisms become maladapted when approaching the limit of their environmental tolerance (‘abundant centre hypothesis&#039;). Energy is a critical resource, especially in winter when environmental conditions deteriorate, and this hypothesis predicts that high energy expenditure (low performance) at the range limit would lead to rapidly dwindling body mass and reduced fitness. We investigated this hypothesis in an Arctic‐breeding seabird wintering in the North Atlantic, the black‐legged kittiwake Rissa tridactyla. From 2008 to 2019, we tracked 117 adult kittiwakes (n = 176 tracks) with geolocation devices and saltwater immersion sensors to estimate the migratory strategies, time–activity budget and energy expenditure of individuals during winter, and estimated their reproductive success after their return to the colony during summer. Population density was indeed higher towards the centre of the range. However, contrary to the predictions, the energy expenditure of individuals was higher at the centre of the range and decreased towards the edge. In contrast, there were no spatial differences in the reproductive success of individuals wintering at the centre versus at the edge of their range. We conclude that performance and fitness did not increase towards the centre of the wintering range, implying that although resource acquisition was likely higher at the abundant centre, energy expenditure was also higher, so that individual fitness was constant across the winter range
La coille noire - Édition, traduction et notes d'après le ms. BnF fr. 837
No full textÉdition, traduction et notes de la Coille noire d'après le ms. BnF fr. 83
Detection, quantification, and characterization by whole-slide image analysis of bacterial infection by Vibrio aestuarianus, stained by immunohistochemistry, in the pacific oyster Magallana gigas
No full textInternational audienceThe growth of marine bivalve aquaculture is presented as a potential measure to effectively provide seafood for human consumption while preserving wild populations. It can be an economic driver in coastal areas while also providing important ecosystem services such as filtration of phytoplankton and carbonate buffering. However, as with other farming practices, increased densities of individuals in a confined space often results in disease outbreaks. Pathogens developing under these conditions can easily spread among farmed stocks, affecting some or possibly most or all production lines, potentially causing adverse economic consequences on the local aquaculture sector, spreading over large areas and eventually affecting wild populations as well. Development and implementation of early detection methods for pathogen infection are imperative to maintain and expand aquaculture activities. In this context, a new method to quantify and characterize infection by Vibrio aestuarianus in the Pacific oyster, Magallana gigas, based on whole-slide image analysis of histological slides stained by immunohistochemistry is presented. The method is used to automatically measure the proportion of tissue infected by IHC-stained bacteria from each image and to characterize bacteria spread in the tissue. The pro portion of tissue infected by IHC-stained bacteria and spatial dispersion indexes, used to characterize 2D bac terial dispersion, were generally associated with the quantity of bacteria previously measured by quantitative polymerase chain reaction (qPCR). These results suggest a pattern of infection where V. aestuarianus tends to be more clustered and less randomly spread in the organism with increased infection. Advantages, limitations, and potential ways to improve the method are discussed