ABSTRACT
We report the results of long-term reverberation mapping campaigns of the nearby active galactic nuclei (AGNs) NGC 4151, spanning from 1994 to 2022, based on archived observations of the ...FAST Spectrograph Publicly Archived Programs and our new observations with the 2.3 m telescope at the Wyoming Infrared Observatory. We reduce and calibrate all the spectra in a consistent way, and derive light curves of the broad H β line and 5100 Å continuum. Continuum light curves are also constructed using public archival photometric data to increase sampling cadences. We subtract the host galaxy contamination using Hubble Space Telescope imaging to correct fluxes of the calibrated light curves. Utilizing the long-term archival photometric data, we complete the absolute flux-calibration of the AGN continuum. We find that the H β time delays are correlated with the 5100 Å luminosities as $\tau _{\rm H\beta }\propto L_{5100}^{0.46\pm 0.16}$. This is remarkably consistent with Bentz et al. (2013)’s global size–luminosity relationship of AGNs. Moreover, the data sets for five of the seasons allow us to obtain the velocity-resolved delays of the H β line, showing diverse structures (outflows, inflows, and discs). Combining our results with previous independent measurements, we find the measured dynamics of the H β broad-line region (BLR) are possibly related to the long-term trend of the luminosity. There is also a possible additional ∼1.86 yr time lag between the variation in BLR radius and luminosity. These results suggest that dynamical changes in the BLR may be driven by the effects of radiation pressure.
Phenology—the timing of biological events—is highly sensitive to climate change. However, our general understanding of how phenology responds to climate change is based almost solely on incomplete ...assessments of phenology (such as first date of flowering) rather than on entire phenological distributions. Using a uniquely comprehensive 39-y flowering phenology dataset from the Colorado Rocky Mountains that contains more than 2 million flower counts, we reveal a diversity of species-level phenological shifts that bring into question the accuracy of previous estimates of long-term phenological change. For 60 species, we show that first, peak, and last flowering rarely shift uniformly and instead usually shift independently of one another, resulting in a diversity of phenological changes through time. Shifts in the timing of first flowering on average overestimate the magnitude of shifts in the timing of peak flowering, fail to predict shifts in the timing of last flowering, and underrepresent the number of species changing phenology in this plant community. Ultimately, this diversity of species-level phenological shifts contributes to altered coflowering patterns within the community, a redistribution of floral abundance across the season, and an expansion of the flowering season by more than I mo during the course of our study period. These results demonstrate the substantial reshaping of ecological communities that can be attributed to shifts in phenology.
Ecological communities consist of species that are joined in complex networks of interspecific interaction. These interactions often form and dissolve rapidly, but this temporal variation is not well ...integrated into our understanding of the causes and consequences of network structure. If interspecific interactions exhibit temporal flexibility across time periods over which organisms co‐occur, then the emergent structure of the corresponding network may also be flexible, something that a temporally‐static perspective will miss. Here, we use an empirical plant–pollinator system to examine short‐term (week‐to‐week) flexibility in network structure (connectance, nestedness and specialization) and in the individual species interactions that contribute to that structure across three summer growing seasons in a subalpine ecosystem. We then compared the properties of weekly networks to the properties of cumulative networks that aggregate field observations over each full summer season. As a test of the potential robustness of networks to perturbation, we also simulated the random loss of species from weekly networks. A week‐to‐week view reveals considerable flexibility in the interactions of individual species and their contributions to network structure. For example, species that would be considered relatively generalized across their entire activity period may be much more specialized at certain times, and at no point as generalized as the cumulative network may suggest. Furthermore, a week‐to‐week view reveals corresponding flexibility in network structure and potential robustness throughout each summer growing season. We conclude that short‐term flexibility in species interactions leads to short‐term variation in network properties, and that a cumulative, season‐long perspective may miss important aspects of the way in which species interact, with implications for understanding their ecology, evolution and conservation.
Whether species interactions are static or change over time has wide‐reaching ecological and evolutionary consequences. However, species interaction networks are typically constructed from temporally ...aggregated interaction data, thereby implicitly assuming that interactions are fixed. This approach has advanced our understanding of communities, but it obscures the timescale at which interactions form (or dissolve) and the drivers and consequences of such dynamics. We address this knowledge gap by quantifying the within‐season turnover of plant–pollinator interactions from weekly censuses across 3 years in a subalpine ecosystem. Week‐to‐week turnover of interactions (1) was high, (2) followed a consistent seasonal progression in all years of study and (3) was dominated by interaction rewiring (the reassembly of interactions among species). Simulation models revealed that species’ phenologies and relative abundances constrained both total interaction turnover and rewiring. Our findings reveal the diversity of species interactions that may be missed when the temporal dynamics of networks are ignored.
The predominant approach for antibody generation remains animal immunization, which can yield exceptionally selective and potent antibody clones owing to the powerful evolutionary process of somatic ...hypermutation. However, animal immunization is inherently slow, not always accessible and poorly compatible with many antigens. Here, we describe ‘autonomous hypermutation yeast surface display’ (AHEAD), a synthetic recombinant antibody generation technology that imitates somatic hypermutation inside engineered yeast. By encoding antibody fragments on an error-prone orthogonal DNA replication system, surface-displayed antibody repertoires continuously mutate through simple cycles of yeast culturing and enrichment for antigen binding to produce high-affinity clones in as little as two weeks. We applied AHEAD to generate potent nanobodies against the SARS-CoV-2 S glycoprotein, a G-protein-coupled receptor and other targets, offering a template for streamlined antibody generation at large.Autonomous hypermutation yeast surface display (AHEAD) mimics the process of somatic hypermutation in animals to enable the rapid in vitro evolution of antibodies, including nanobodies targeting the RBD of SARS-CoV-2.
Abstract We report first-time reverberation-mapping results for 14 active galactic nuclei (AGNs) from the ongoing Monitoring AGNs with H β Asymmetry campaign (MAHA). These results utilize optical ...spectra obtained with the Long Slit Spectrograph on the Wyoming Infrared 2.3 m Telescope between 2017 November and 2023 May. MAHA combines long-duration monitoring with high cadence. We report results from multiple observing seasons for nine of the 14 objects. These results include H β time lags, supermassive black hole masses, and velocity-resolved time lags. The velocity-resolved lags allow us to investigate the kinematics of the broad-line region.
Humoral responses in coronavirus disease 2019 (COVID-19) are often of limited durability, as seen with other human coronavirus epidemics. To address the underlying etiology, we examined post mortem ...thoracic lymph nodes and spleens in acute SARS-CoV-2 infection and observed the absence of germinal centers and a striking reduction in Bcl-6+ germinal center B cells but preservation of AID+ B cells. Absence of germinal centers correlated with an early specific block in Bcl-6+ TFH cell differentiation together with an increase in T-bet+ TH1 cells and aberrant extra-follicular TNF-α accumulation. Parallel peripheral blood studies revealed loss of transitional and follicular B cells in severe disease and accumulation of SARS-CoV-2-specific “disease-related” B cell populations. These data identify defective Bcl-6+ TFH cell generation and dysregulated humoral immune induction early in COVID-19 disease, providing a mechanistic explanation for the limited durability of antibody responses in coronavirus infections, and suggest that achieving herd immunity through natural infection may be difficult.
Display omitted
•Germinal centers are lost in lymph nodes and spleens in acute COVID-19•Bcl-6+ GC B cells and Bcl-6+ T follicular helper cells are markedly diminished•Abundant TH1 cells and aberrant TNF-α production are seen in COVID-19 lymph nodes•SARS-CoV-2-specific activated B cells accumulate in the blood of patients
Shiv Pillai and colleagues show that in acute COVID-19, there is a striking loss of germinal centers in lymph nodes and spleens and depletion of Bcl-6+ B cells but preservation of AID+ B cells. A specific block in germinal center type Bcl-6+ T follicular helper cell differentiation may explain the loss of germinal centers and the accumulation of non-germinal-center-derived activated B cells. These data suggest an underlying basis for the lower quality and lack of durability of humoral immune responses observed during natural infection with SARS-CoV-2 and have significant implications for expectations of herd immunity.
We show that SARS-CoV-2 spike protein interacts with both cellular heparan sulfate and angiotensin-converting enzyme 2 (ACE2) through its receptor-binding domain (RBD). Docking studies suggest a ...heparin/heparan sulfate-binding site adjacent to the ACE2-binding site. Both ACE2 and heparin can bind independently to spike protein in vitro, and a ternary complex can be generated using heparin as a scaffold. Electron micrographs of spike protein suggests that heparin enhances the open conformation of the RBD that binds ACE2. On cells, spike protein binding depends on both heparan sulfate and ACE2. Unfractionated heparin, non-anticoagulant heparin, heparin lyases, and lung heparan sulfate potently block spike protein binding and/or infection by pseudotyped virus and authentic SARS-CoV-2 virus. We suggest a model in which viral attachment and infection involves heparan sulfate-dependent enhancement of binding to ACE2. Manipulation of heparan sulfate or inhibition of viral adhesion by exogenous heparin presents new therapeutic opportunities.
Display omitted
•SARS-CoV-2 spike protein interacts with heparan sulfate and ACE2 through the RBD•Heparan sulfate promotes Spike-ACE2 interaction•SARS-CoV-2 infection is co-dependent on heparan sulfate and ACE2•Heparin and non-anticoagulant derivatives block SARS-CoV-2 binding and infection
Clausen et al. provide evidence that heparan sulfate is a necessary co-factor for SARS-CoV-2 infection. They show that heparan sulfate interacts with the receptor-binding domain of the SARS-CoV-2 spike glycoprotein, adjacent to ACE2, shifting the spike structure to an open conformation to facilitate ACE2 binding.
Climate change is rapidly altering thermal environments across the globe. The effects of increased temperatures in already warm environments may be particularly strong because organisms are likely to ...be near their thermal safety margins, with limited tolerance to additional heat stress.
We conduct an in situ field experiment over 2 years to investigate the direct effects of temperature change on an early‐season solitary bee in a warm, arid region of the Southwestern USA. Our field experiment manipulates the thermal environment of Osmia ribifloris (Megachilidae) from larval development through adult emergence, simulating both previous cooler (c. 1950; nest boxes painted white) and future warmer (2040–2099; nest boxes painted black) climate conditions. In each year, we measure adult emergence phenology, linear body size, body mass, fat content and survival.
Bees in the warming treatment exhibit delayed emergence phenology and a substantial increase in phenological variance. Increases in temperature also lead to reductions in body mass and fat content. Whereas bees in the cooling and control treatments experience negligible amounts of mortality, bees in the warming treatment experience 30%–75% mortality.
Our findings indicate that temperature changes that have occurred since c. 1950 have likely had relatively weak and non‐negative effects, but predicted warmer temperatures create a high stress thermal environment for O. ribifloris. Later and more variable emergence dates under warming likely compromise phenological synchrony with floral resources and the ability of individuals to find mates. The consequences of phenological asynchrony, combined with reductions in body mass and fat content, will likely impose fitness reductions for surviving bees. Combined with high rates of mortality, our results suggest that O. ribifloris may face local extinction in the warmer parts of its range within the century under climate change.
Temperature increases in already warm ecosystems can have substantial consequences for key components of life history, physiology and survival. Our study provides an important example of how the responses of ectothermic insects to temperature increases in already warm environments may be insufficient to mitigate the negative consequences of future climate change.
A plain language summary is available for this article.
Plain Language Summary
When a phenological shift affects a demographic vital rate such as survival or reproduction, the altered vital rate may or may not have population-level consequences. We review the evidence that ...climate change affects populations by shifting species' phenologies, emphasizing the importance of demographic life-history theory. We find many examples of phenological shifts having both positive and negative consequences for vital rates. Yet, few studies link phenological shifts to changes in vital rates known to drive population dynamics, especially in plants. When this link is made, results are largely consistent with life-history theory: Phenological shifts have population-level consequences when they affect survival in longer-lived organisms and reproduction in shorter-lived organisms. However, there are just as many cases in which demographic mechanisms buffer population growth from phenologically induced changes in vital rates. We provide recommendations for future research aiming to understand the complex relationships among climate, phenology, and demography, which will help to elucidate the extent to which phenological shifts actually alter population persistence.
PDF
