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Making sense of variation in sclerochronological stable isotope profiles of mollusks and fish otoliths from the early Eocene southern North Sea Basin
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Stable isotope sclerochemistry of biogenic carbonate is frequently used for the reconstruction of paleotemperature and seasonality. Yet, few studies have compared intra-and inter-taxon isotope variability and variation within a single depositional environment. We measured seasonal changes in δ18O and δ13C compositions in multiple specimens of two carditid bivalve species, a turritelline gastropod species, and two species of otoliths from demersal fish, from two early Eocene (latest Ypresian, 49.2 Ma) coquinas in the inner neritic Aalter Formation, located in the Belgian part of the southern North Sea Basin (paleolatitude ∼41°N). Results demonstrate considerable variation among taxa in the mean, amplitude, and skewness of δ18O and δ13C values from sequentially sampled growth series. We attribute this variation to factors including differences in seasonal growth over ontogeny, mixing of depositional settings by sediment transport, differences between sedentary and mobile organisms, and differences in longevity of the taxa in question. Growth cessation during winters in turritellines and fishes in particular lead to an incomplete representation of the seasonal cycle in their growth increments, in comparison to carditid bivalves. Ophidiid fish otolith isotope records appear to reflect environmental conditions over a wider range of habitats and environments, and we infer this is due to a combination of sedimentary transport, as these are small structures, and postmortem transport by free-swimming predatory fish. Our study highlights the potential variability encompassed by taxa in the shallow marine realm even when they are found in the same deposits. While this has significant implications for seasonality reconstructions based on conventional isotope profiles, we show that careful study of the ecology and ontogeny of multiple taxa and specimens within a death assemblage can reveal sources of variation and yield a close approximation of conditions in the setting of interest.
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Modelling migratory waterfowl stopover habitat while accounting for ephemeral environmental conditions
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1.Migratory species depend on ephemeral environmental conditions; thus, species distribution modelling (SDM) must incorporate phenological changes along migratory routes. Our overarching goal was to model habitats for three waterfowl species migrating through Eurasian grasslands (red-breasted goose [Branta ruficollis], taiga bean goose [Anser fabalis fabalis] and Bewick's swan [Cygnus columbianus bewickii]) while accounting for ephemeral environmental conditions. Our objectives were (a) to develop a workflow of mapping ephemeral environmental conditions, (b) model habitats for the three species and (c) evaluate the protection status of habitats in natural and agricultural landscapes. We expected water availability, particularly ephemeral spring waterbodies, to strongly influence these species' distributions. 2. We utilized MODIS data for phenological synchronization of Landsat images to create species-and season-specific metrics and land cover maps. We used Landsat-derived environmental variables, elevation and bird GPS locations in Maxent SDM. We compared locations of modelled habitats, protected areas and Ramsar sites. 3. Our land cover maps had an overall accuracy of 0.92–0.95 and captured ephemeral water extent during these species' migrations. All models had AUC scores of 0.89–0.94; distance to water, land cover and elevation were the most important variables. Modelled habitats were distributed unevenly and occurred in both natural and agricultural landscapes; 40%–76% fell within croplands. Although most croplands provide a rich food supply, their value as waterfowl habitat critically depended on water availability. Approximately 22% of potential habitat in the natural landscape, but only 3% in croplands, had some level of protection.
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Temporal Changes to Migratory Fuel Load in Migratory Birds Across Europe
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Climate change is a major threat to biodiversity, and migratory animals are particularly vulnerable, due partly to their reliance upon good resource availability across a network of sites at specific times. Migrants perform vital ecosystem functions, transferring significant resources across large spatial scales, but the impacts of climate change on the ability of individuals to complete these journeys are poorly studied. Collecting the large-scale and long-term data on the condition of individuals during migration to address this is challenging, but in migratory birds, we have a model system for which a large network of ringers (banders) collect individual data on body size and mass, enabling variation in body condition to be tracked. We used long-term ringing data on 33 Afro–Palearctic migratory bird species at 286 sites across Europe to demonstrate a large-scale decrease in migratory fuel loads during autumn over the last 40 years, but not in spring. Declines were strongest across southern Europe and linked to rising temperatures. The timing of autumn fuelling has also shifted, occurring earlier at northern sites and later at southern sites. These relationships varied depending on diet and breeding cycle length. Obligate insectivores were more constrained by temperature in the timing and magnitude of fuelling than frugivores. Species with short breeding cycles departed later at southern sites in warmer years, likely reflecting an extended breeding season. Altogether, these latitudinally varying findings suggest a trade-off between maximising productivity or maximising adult survival as climate drives changing constraints on breeding season length and resource availability. Similar climate-induced trade-offs may be happening in other migratory taxa with the potential to influence population trends.
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Reducing sand mining’s growing toll on mareine biodiversity
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RBINS Staff Publications 2025 OA
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Vertical dynamics of suspended particulate matter and chlorophyll-a in a well-mixed coastal turbid system
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RBINS Staff Publications 2025 OA
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Spatio‑temporal variation in particulate and dissolved organic matter dynamics in the southern North Sea
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Phytoplankton enhances the flocculation of suspended particulate matter in a turbid estuary
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Major excursions in sulfur isotopes linked to permafrost change in Eurasia during the last 50,000 years.
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We identify a major sulfur isotope excursion in Eurasian faunal bone collagen from the last 50,000 years, here termed the Late Pleniglacial Sulfur Excursion. Our analysis suggests this is linked to changing permafrost conditions, presenting the utility of faunal collagen δ34S as a proxy for permafrost dynamics, a critical component of the global carbon cycle. Our findings complicate the use of archaeological faunal sulfur isotopes for mobility and palaeodietary studies.
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Genome analyses suggest recent speciation and postglacial isolation in the Norwegian lemming
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The Norwegian lemming (Lemmus lemmus) is a small rodent distributed across the Fennoscandian mountain tundra and the Kola Peninsula. The Norwegian lemming likely evolved during the Late Pleistocene and inhabited Fennoscandia shortly prior to the Last Glacial Maximum. However, the exact timing and origins of the species, and its phylogenetic position relative to the closely related Siberian lemming (Lemmus sibiricus) remain disputed. Moreover, the presence of ancient or contemporary gene flow between both species is largely untested. The Norwegian lemming displays characteristic phenotypic and behavioral adaptations (e.g., coat color, aggression) that are not present in other Lemmus species. We generated a de novo genome assembly for the Norwegian lemming and resequenced nine modern and two ancient Lemmus spp. genomes. We show that all Lemmus species form distinct monophyletic clades, with concordant topology between the mitochondrial and nuclear genome phylogenies. The Siberian lemming is divided into two distinct but paraphyletic clades, one in the east and one in the west, where the western clade represents a sister taxon to the Norwegian lemming. We estimate that the Norwegian and western Siberian lemming diverged shortly before the Last Glacial Maximum, making the Norwegian lemming one of the youngest known mammalian species. We did not find any indication of gene flow between L. lemmus and L. sibiricus, suggesting postglacial isolation of L. lemmus. Furthermore, we identify species-specific genomic differences in genes related to coat color and fat transport, which are likely associated with the distinctive coloration and overwintering behavior observed in the Norwegian lemming.
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A Million Years of Mammoth Mitogenome Evolution.
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The genomic study of specimens dating to the Early and Middle Pleistocene (EP and MP), a period spanning from 2.6 million years ago (Ma) to 126 thousand years ago (ka), has the potential to elucidate the evolutionary processes that shaped present-day biodiversity. Obtaining genomic data from this period is challenging, but mitochondrial DNA, given its higher abundance compared to nuclear DNA, could play an important role to understand evolutionary processes at this time scale. In this study, we report 34 new mitogenomes, including two EP and nine MP mammoth (Mammuthus spp.) specimens from Siberia and North America and analyze them jointly with >200 publicly available mitogenomes to reconstruct a transect of mammoth mitogenome diversity throughout the last million years. We find that our EP mitogenomes fall outside the diversity of all Late Pleistocene (LP) mammoths, while those derived from MP mammoths are basal to LP mammoth Clades 2 and 3, supporting an ancient Siberian origin of these lineages. In contrast, the geographical origin of Clade 1 remains unresolved. With these new deep-time mitogenomes, we observe diversification events across all clades that appear consistent with previously hypothesized MP and LP demographic changes. Furthermore, we improve upon an existing methodology for molecular clock dating of specimens >50 ka, demonstrating that specimens need to be individually dated to avoid biases in their age estimates. Both the molecular and analytical improvements presented here highlight the importance of deep-time genomic data to discover long-lost genetic diversity, enabling better assessments of evolutionary histories.
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