Pathogens, like other consumers, mediate the outcome of competitive interactions between their host species. Ongoing efforts to integrate pathogens into plant community ecology could be accelerated ...by greater conceptual unification. Research on plant pathogens has mainly focused on a variety of disparate mechanisms-—the Janzen-Connell hypothesis, plant-–soil feedbacks, competition-–defense trade-offs, escape of invasive plants from their enemies, and epidemic-driven community shifts-—with limited recognition of how these mechanisms fit into the broader context of plant coexistence. Here, I extend an emerging theoretical framework for understanding species coexistence to include various pathogen impacts on plant communities. Pathogens can promote coexistence by regulating relative abundance or by reducing the disparities between species in fitness that make coexistence more difficult. Conversely, pathogens may undermine coexistence by creating positive feedbacks or by increasing between-species fitness differences. I review the evidence for these pathogen-mediated mechanisms, and I reframe the major hypotheses in a community ecology context in order to understand how the mechanisms are related. This approach generates predictions about how various modes of pathogen attack affect plant coexistence, even when direct impacts on host relative abundance are difficult to measure. Surprisingly, no study gives direct empirical evidence for pathogen effects on mutual invasibility, a key criterion for coexistence. Future studies should investigate the relationship between pathogen attack and host relative abundance, in order to distinguish between mechanisms.
Reducing the burden of neglected tropical diseases (NTDs) is one of the key strategic targets advanced by the Sustainable Development Goals. Despite the unprecedented effort deployed for NTD ...elimination in the past decade, their control, mainly through drug administration, remains particularly challenging: persistent poverty and repeated exposure to pathogens embedded in the environment limit the efficacy of strategies focused exclusively on human treatment or medical care. Here, we present a simple modelling framework to illustrate the relative role of ecological and socio-economic drivers of environmentally transmitted parasites and pathogens. Through the analysis of system dynamics, we show that periodic drug treatments that lead to the elimination of directly transmitted diseases may fail to do so in the case of human pathogens with an environmental reservoir. Control of environmentally transmitted diseases can be more effective when human treatment is complemented with interventions targeting the environmental reservoir of the pathogen. We present mechanisms through which the environment can influence the dynamics of poverty via disease feedbacks. For illustration, we present the case studies of Buruli ulcer and schistosomiasis, two devastating waterborne NTDs for which control is particularly challenging.
This article is part of the themed issue ‘Conservation, biodiversity and infectious disease: scientific evidence and policy implications’.
Aedes-borne diseases, such as dengue and chikungunya, are responsible for more than 50 million infections worldwide every year, with an overall increase of 30-fold in the last 50 years, mainly due to ...city population growth, more frequent travels and ecological changes. In the United States of America, the vast majority of Aedes-borne infections are imported from endemic regions by travelers, who can become new sources of mosquito infection upon their return home if the exposed population is susceptible to the disease, and if suitable environmental conditions for the mosquitoes and the virus are present. Since the susceptibility of the human population can be determined via periodic monitoring campaigns, the environmental suitability for the presence of mosquitoes and viruses becomes one of the most important pieces of information for decision makers in the health sector. We present a next-generation monitoring and forecasting system for Formula: see text-borne diseases' environmental suitability (AeDES) of transmission in the conterminous United States and transboundary regions, using calibrated ento-epidemiological models, climate models and temperature observations. After analyzing the seasonal predictive skill of AeDES, we briefly consider the recent Zika epidemic, and the compound effects of the current Central American dengue outbreak happening during the SARS-CoV-2 pandemic, to illustrate how a combination of tailored deterministic and probabilistic forecasts can inform key prevention and control strategies .
Several plant pathogenic Parastagonospora species have been identified infecting wheat and other cereals over the past 50 years. As new lineages were discovered, naming conventions grew unwieldy and ...the relationships with previously recognized species remained unclear. We used genome sequencing to clarify relationships among these species and provided new names for most of these species. Six of the nine described Parastagonospora species were recovered from wheat, with five of these species coming from Iran. Genome sequences revealed that three strains thought to be hybrids between P. nodorum and P. pseudonodorum were not actually hybrids, but rather represented rare gene introgressions between those species. Our data are consistent with the hypothesis that P. nodorum originated as a pathogen of wild grasses in the Fertile Crescent, then emerged as a wheat pathogen via host-tracking during the domestication of wheat in the same region. The discovery of a diverse array of Parastagonospora species infecting wheat in Iran suggests that new wheat pathogens could emerge from this region in the future.
PURPOSEToll-like receptor 4 (TLR4) is an inflammatory receptor expressed ubiquitously in immune cells as well as skeletal muscle and other metabolic tissues. Skeletal muscle develops favorable ...inflammation-mediated metabolic adaptations from exercise training. Multiple inflammatory myokines, downstream from TLR4, are proposed links to the metabolic benefits of exercise. Additionally, activation of TLR4 alters skeletal muscle substrate preference. The role of skeletal muscle TLR4 (mTLR4) in exercise metabolism has not previously been investigated. Herein, we aimed to specifically test the significance of mTLR4 to exercise-induced metabolic adaptations.
METHODSWe developed a novel muscle-specific TLR4 knockout (mTLR4) mouse model on C57BL/6J background. Male mTLR4 mice and wild type (WT) littermates were compared under sedentary (SED) and voluntary wheel running (WR) conditions for 4 weeks.
RESULTSmTLR4 deletion revealed marked reductions in downstream interleukin-1 receptor-associated kinase-4 (IRAK4) phosphorylation. In addition, the disruption of mTLR4 signaling prominently blunted the metabolic adaptations in WR-mTLR4 mice as oppose to substantial improvements exhibited by the WT counterparts. Voluntary WR in WT mice, relative to SED, resulted in significant increases in skeletal muscle fatty acid oxidation (FAO), glucose oxidation (GO), and associated mitochondrial enzyme activities, all of which were not significantly changed in mTLR4 mice.
CONCLUSIONThis study introduces a novel mTLR4 mouse model and identifies mTLR4 as an immunomodulatory effector of exercise-induced metabolic adaptations in skeletal muscle.
The merger rate of stellar-mass black hole binaries (sBHBs) inferred by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) suggests the need for an efficient source of sBHB ...formation. Active galactic nucleus (AGN) disks are a promising location for the formation of these sBHBs, as well as binaries of other compact objects, because of powerful torques exerted by the gas disk. These gas torques cause orbiting compact objects to migrate toward regions in the disk where inward and outward torques cancel, known as migration traps. We simulate the migration of stellar mass black holes in an example of a model AGN disk, using an augmented N-body code that includes analytic approximations to migration torques, stochastic gravitational forces exerted by turbulent density fluctuations in the disk, and inclination and eccentricity dampening produced by passages through the gas disk, in addition to the standard gravitational forces between objects. We find that sBHBs form rapidly in our model disk as stellar-mass black holes migrate toward the migration trap. These sBHBs are likely to subsequently merge on short timescales. The process continues, leading to the build-up of a population of over-massive stellar-mass black holes. The formation of sBHBs in AGN disks could contribute significantly to the sBHB merger rate inferred by LIGO.
ABSTRACT Accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGNs) contain stars, stellar mass black holes, and other stellar remnants, which perturb the disk gas ...gravitationally. The resulting density perturbations exert torques on the embedded masses causing them to migrate through the disk in a manner analogous to planets in protoplanetary disks. We determine the strength and direction of these torques using an empirical analytic description dependent on local disk gradients, applied to two different analytic, steady-state disk models of SMBH accretion disks. We find that there are radii in such disks where the gas torque changes sign, trapping migrating objects. Our analysis shows that major migration traps generally occur where the disk surface density gradient changes sign from positive to negative, around 20-300Rg, where Rg = 2GM/c2 is the Schwarzschild radius. At these traps, massive objects in the AGN disk can accumulate, collide, scatter, and accrete. Intermediate mass black hole formation is likely in these disk locations, which may lead to preferential gap and cavity creation at these radii. Our model thus has significant implications for SMBH growth as well as gravitational wave source populations.
Understanding the formation of stellar clusters requires following the interplay between gas and newly formed stars accurately. We therefore couple the magnetohydrodynamics code FLASH to the N-body ...code ph4 and the stellar evolution code SeBa using the Astrophysical Multipurpose Software Environment (AMUSE) to model stellar dynamics, evolution, and collisional N-body dynamics and the formation of binary and higher-order multiple systems, while implementing stellar feedback in the form of radiation, stellar winds, and supernovae in FLASH. We here describe the algorithms used for each of these processes. We denote this integrated package Torch. We then use this novel numerical method to simulate the formation and early evolution of several examples of open clusters of ∼1000 stars formed from clouds with a mass range of 103 M to 105 M . Analyzing the effects of stellar feedback on the gas and stars of the natal clusters, we find that in these examples, the stellar clusters are resilient to disruption, even in the presence of intense feedback. This can even slightly increase the amount of dense, Jeans unstable gas by sweeping up shells; thus, a stellar wind strong enough to trap its own H ii region shows modest triggering of star formation. Our clusters are born moderately mass segregated, an effect enhanced by feedback, and retained after the ejection of their natal gas, in agreement with observations.
The masses, rates, and spins of merging stellar mass binary black holes (BBHs) detected by aLIGO and Virgo provide challenges to traditional BBH formation and merger scenarios. An active galactic ...nucleus (AGN) disk provides a promising additional merger channel because of the powerful influence of the gas that drives orbital evolution, makes encounters dissipative, and leads to migration. Previous work showed that stellar mass black holes (sBHs) in an AGN disk migrate to regions of the disk, known as migration traps, where positive and negative gas torques cancel out, leading to frequent BBH formation. Here we build on that work by simulating the evolution of additional sBHs that enter the inner disk by either migration or inclination reduction. We also examine whether the BBHs formed in our models have retrograde or prograde orbits around their centers of mass with respect to the disk, determining the orientation of the spin of the merged BBHs relative to the disk. Orbiters entering the inner disk form BBHs with sBHs on resonant orbits near the migration trap. When these sBHs reach 80 M☉, they form BBHs with sBHs in the migration trap, which reach ∼1000 M☉ over 10 Myr. We find 68% of the BBHs in our simulation orbit in the retrograde direction, which implies that BBHs in our merger channel will have small dimensionless aligned spins, χeff. Overall, our models produce BBHs that resemble both the majority of BBH mergers detected thus far (0.66-120 Gpc−3 yr−1) and two recent unusual detections, GW190412 (∼0.3 Gpc−3 yr−1) and GW190521 (∼0.1 Gpc−3 yr−1).
We describe a star cluster formation model that includes individual star formation from self-gravitating, magnetized gas, coupled to collisional stellar dynamics. The model uses the Astrophysical ...Multi-purpose Software Environment to integrate an adaptive-mesh magnetohydrodynamics code (FLASH) with a fourth order Hermite N-body code (ph4), a stellar evolution code (SeBa), and a method for resolving binary evolution (multiples). This combination yields unique star-formation simulations that allow us to study binaries formed dynamically from interactions with both other stars and dense, magnetized gas subject to stellar feedback during the birth and early evolution of stellar clusters. We find that for massive stars, our simulations are consistent with the observed dynamical binary fractions and mass ratios. However, our binary fraction drops well below observed values for lower mass stars, presumably due to unincluded binary formation during initial star formation. Further, we observe a buildup of binaries near the hard-soft boundary that may be an important mechanism driving early cluster contraction.
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