Biology subjects

Schmidt, N. M.

Publications and source records attributed to Schmidt, N. M..

6 recordsLinked to original sources

bioRxiv2026

Inferences about phenological shifts in an Arctic community vary with time-windows

Long-term monitoring data have enabled detection of phenological change, yet it remains poorly understood how its temporal dimensions-- duration and choice of start and end years-- influence the inferences drawn. To examine which phenological signals emerge at different temporal scales, we analyzed the longest continuous dataset on high-arctic plant and arthropod phenology, collected from 1996 to 2024 in the Zackenberg valley, northeast Greenland. These data have been used to suggest both rapid advancement of spring in the High Arctic (2007) and little directional change but decadal regime shifts (2023). To reconcile these differing conclusions, we quantified how trend estimates varied across moving time-windows and determined the minimum time-series length required to achieve a high probability of agreement with long-term trends. We find that while trend directionality shifts with temporal windows, confidence in trend estimates increases with time-series length. Using the full time-series, we show dampened signals of warming trends, with annual increases in spring and summer air temperatures by 0.04 [-0.05, 0.13] and 0.05 [-0.01, 0.11] {degrees}C per year, respectively, alongside a 0.82% [-1.85, 0.19] decline in spring snow cover. We also see modest advancement in the seasonal activity of most arthropod taxa (by [~]0.1 days/year), whereas flowering phenology shows no consistent directional change. Shorter time-series revealed cyclical patterns in abiotic drivers yet variable biotic responses, indicating that a single pattern of "climate change" will translate into varied responses within communities. Finally, almost two decades of data were needed to reliably capture long-term trends. Ecologically, these suggest that 1) phenological shifts in the High Arctic are more moderate than early assessments implied and 2) reflect a dynamic balance between species life histories and ongoing climate variability. These may alter interaction potentials within communities, with consequences for ecosystem functioning.

ecology↗

bioRxiv2024

Opportunistic partner choice among arctic plants and root-associated fungi is driven by environmental conditions.

Interactions between plants and soil microbes play an important role in structuring plant communities. Yet, little is known about how fungal networks are structured on the one hand by fungal responses to their environment (including their host plant) and on the other by responses to each other. We quantified changes in plant-fungus networks along geographic and environmental gradients across the Arctic, assessing the degree to which plants and fungi showed preference for specific interaction partners and how specificity varies along environmental gradients. To this aim, we sampled roots of 12 widely distributed plant taxa: Saxifraga oppositifolia; Bistorta vivipara; Dryas spp.; Vaccinium tis-idaea; Vaccinium uliginosum; Vaccinium myrtillus; Empetrum nigrum; Betula nana; alix arctica; Salix polaris; Cassiope tetragona; and Silene acaulis. To quantify the pool of fungi from which plant roots may recruit association partners, we also sampled fungi in the surrounding soil. Identifying fungaI communities by DNA metabarcoding, we used Hierarchical Modelling of Species Communities (HMSC) to assess how fungal communities change along environmental gradients, and whether plants actively select their root-associated fungi from the pool of fungi present in the bulk soil. We found that although the fungal communities within the soil and rhizosphere share 85% of genera, their composition differs significantly from each other. The two community types show similar responses to the environment and taxa show low partner fidelity. Thus, the structure of fungal communities on plant rhizosphere is mainly driven by abiotic rather than biotic conditions. Overall, in comparison with null models, networks of plants and rhizosphere-associated fungi showed a distinctly non-random structure, responding strongly to pH and temperature gradients. Our findings suggest that the dynamics and structure of plant-root associated interactions might be severely altered by abiotic changes in the rapidly changing arctic environment. Open Research statementData are privately provided for peer review. The raw sequences for the soil and root samples generated during the current study will be available in the Sequence Read Archive repository, in the BioProject PRJNA1094865 upon acceptance. For review purposes, the code and datasets used for the analyses of this study are temporarily available in Figshare open access repository at https://figshare.com/s/1b074f1751682d3487cf upon acceptance.

ecology↗

bioRxiv2023

Multiple Pleistocene refugia for Arctic White Heather (Cassiope tetragona) supported by population genomics analyses of contemporary and Little-Ice-Age samples

AimArctic plants survived the Pleistocene glaciations in unglaciated refugia, but the number of these refugia is often unclear. We use high-resolution genomic data from present-day and Little-Ice-Age populations of Arctic White Heather (Cassiope tetragona) to re-evaluate the biogeography of this species and determine whether it had multiple independent refugia or a single refugium in Beringia. LocationCircumpolar Arctic and Coastal British Columbia (BC) alpine TaxonCassiope tetragona L., subspecies saximontana and tetragona, outgroup C. mertensiana (Ericaceae) MethodsWe built genotyping-by-sequencing (GBS) libraries using Cassiope tetragona tissue from 36 Arctic locations, including two [~]250-500-year-old populations collected under glacial ice on Ellesmere Island, Canada. We assembled a de novo GBS reference and called variants in dDocent. Population structure, genetic diversity, and demography were inferred from PCA, ADMIXTURE, fastsimcoal2, SplitsTree, and several population genomics statistics. ResultsPopulation structure analyses identified 4-5 clusters that align with geographic locations. Nucleotide diversity was highest in Beringia and decreased eastwards across Canada. Demographic coalescent analysis of the site-frequency-spectrum dated the following splits from Alaska: BC subspecies saximontana (6 mya), Russia (1.5 mya), Europe (>300-600 kya), Greenland (100 kya). Northern Canada populations appear to be from the current interglacial (7-9 kya). Genetic variants from Alaska appeared more frequently in present-day than historic plants on Ellesmere Island. ConclusionsDemographic analyses show BC, Alaska, Russia, Europe, and Greenland all had separate refugia during the last major glaciations. Northern Canadian populations appear to be founded during the current interglacial with genetic contributions from Alaska, Europe, and Greenland. On Ellesmere Island, there is evidence for continued, recent gene flow with foreign variants introduced in the last 250-500 years. These results suggest that a re-analysis of other Arctic species with shallow population structure using higher resolution genomic markers and demographic analyses may help reveal deeper structure and other circumpolar glacial refugia.

genomics↗

bioRxiv2023

Site-specific length-biomass relationships of arctic arthropod families are critical for accurate ecological inferences

Arthropods play an essential role in terrestrial ecosystems, not least by forming the food base for insectivorous birds. To better understand such trophic interactions, it is essential to monitor seasonal trajectories in arthropod biomass. Because obtaining direct measurements of the body mass of individual specimens is laborious, these data are often indirectly acquired by utilizing allometric length-biomass relationships based on a correlative parameter, such as body length. Studies on insectivorous birds have often used such relationships with a low taxonomic resolution and/or small sample size and/or adopted regressions calibrated in different biomes. Despite the scientific interest in the ecology of arctic arthropods, no site-specific family-level length-biomass relationships have hitherto been published. Here we present 27 family-specific length-biomass relationships from two sites in the High Arctic: Zackenberg in northeast Greenland and Knipovich in north Taimyr, Russia. We show that length-biomass regressions from different sites within the same biome did not affect estimates of phenology but did result in substantially different estimates of arthropod biomass. Estimates of daily biomass at Zackenberg were on average 24% higher when calculated using regressions for Knipovich compared to using regressions for Zackenberg. Our results illustrate that the use of allometric relationships from different sites can significantly alter the biological interpretation of, for instance, the interaction between insectivorous birds and their arthropod prey. We conclude that length-biomass relationships should be locally established rather than being based on global relationships. SubjectsEcology, Entomology, Terrestrial ecology

ecology↗

bioRxiv2022

An ACAT inhibitor regulates SARS-CoV-2 replication and antiviral T cell activity

The severity of disease following infection with SARS-CoV-2 is determined by viral replication kinetics and host immunity, with early T cell responses and/or suppression of viraemia driving a favourable outcome. Recent studies have uncovered a role for cholesterol metabolism in the SARS-CoV-2 life cycle and in T cell function. Here we show that blockade of the enzyme Acyl-CoA:cholesterol acyltransferase (ACAT) with Avasimibe inhibits SARS-CoV-2 entry and fusion independent of transmembrane protease serine 2 expression in multiple cell types. We also demonstrate a role for ACAT in regulating SARS-CoV-2 RNA replication in primary bronchial epithelial cells. Furthermore, Avasimibe boosts the expansion of functional SARS-CoV-2-specific T cells from the blood of patients sampled in the acute phase of infection. Thus, re-purposing of available ACAT inhibitors provides a compelling therapeutic strategy for the treatment of COVID-19 to achieve both antiviral and immunomodulatory effects.

immunology↗

bioRxiv2020

Taxonomic, temporal, and spatial variation in the dynamics of High-Arctic arthropod populations

Time-series data on arthropod populations are critical for understanding the magnitude, direction, and drivers of abundance changes. However, most arthropod monitoring programs are short-lived and limited in taxonomic resolution and spatial extent. Consequently, variation in population dynamics among taxa and habitats remains poorly understood. Monitoring data from the Arctic are particularly underrepresented, yet important to assessments of species abundance changes because many anthropogenic drivers of change that are present in other regions are absent in polar regions. Here, we utilise 24 years of abundance data from Zackenberg in High-Arctic Greenland, which is the longest running Arctic arthropod monitoring program, to study temporal trends in abundance. Despite a strong warming signal in air temperature, we only find evidence of weak temporal trends in arthropod abundances across most taxa. These trends are more pronounced in the most recent decade, with change point analyses suggesting distinct non-linear dynamics within some functional groups such as predators and detritivores. Although the abundances of many taxa were correlated, we detected both positive and negative correlations, suggesting that multiple processes are affecting arthropod populations even in this relatively simple Arctic food web. Finally, we found clear differences among species within single families of arthropods, indicating that an apparent lack of change in abundance at broader taxonomic or functional levels could mask substantial species-specific trends. Our results reiterate the need for more basic research into the life-history, ecology, and adaptation of arthropod species to better understand their sensitivity to global changes. Significance statementTerrestrial arthropods, including insects and spiders, serve critical ecosystem functions and are excellent indicators of environmental change due to their physiology, short generation time, and abundance. The Arctic, with its rapid climate change and limited direct anthropogenic impact, is ideal for examining arthropod population dynamics. We use the most comprehensive, standardized dataset available on Arctic arthropods to evaluate the variability in population dynamics for the most common arthropod groups at various taxonomic levels across 24 years. Our results highlight that temporal trends of arthropod populations seem less directional in the Arctic than in temperate regions. Although abundances of some arthropod taxa are declining, particularly in recent decades, population trends still display high variation among time periods, taxa, and habitats.

ecology↗