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Natural killer (NK) cells are innate lymphoid cells that protect a host from viral infections and malignancies. MicroRNA-146a (miR-146a) is an important regulator of immune function that is highly expressed in NK cells and is further upregulated during murine cytomegalovirus (MCMV) infection. Here we utilized mice with a global targeted deletion of miR-146a to understand its impact on the innate immune responses to MCMV infection. MiR-146a-/- mice were protected from lethal MCMV infection, which was intrinsic to the hematopoietic compartment based on bone marrow chimera experiments. NK cell depletion abrogated this protection, implicating NK cells as critical for the miR-146a-/- protection from MCMV. Surprisingly, NK cells from miR-146a-deficient mice were largely similar to control NK cells with respect to development, maturation, trafficking, and effector functions. However, miR-146a-/- mice had increased NK cell numbers and frequency of the most mature Stage IV (CD27-CD11b+) NK cells in the liver at baseline, enhanced STAT1 phosphorylation, and increased selective expansion of Ly49H+ NK cells and T cells during MCMV infection. This study demonstrates a critical role for miR-146a in the host response to MCMV, arising from mechanisms that include increased NK cell numbers and early T-cell expansion.
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Animals adapt to environmental conditions by modifying the function of their internal organs, including the brain. To be adaptive, alterations in behavior must be coordinated with the functional state of organs throughout the body. Here, we find that thyroid hormone-a regulator of metabolism in many peripheral organs-directly activates cell-type-specific transcriptional programs in the frontal cortex of adult male mice. These programs are enriched for axon-guidance genes in glutamatergic projection neurons, synaptic regulatory genes in both astrocytes and neurons, and pro-myelination factors in oligodendrocytes, suggesting widespread plasticity of cortical circuits. Indeed, whole-cell electrophysiology revealed that thyroid hormone alters excitatory and inhibitory synaptic transmission, an effect that requires thyroid hormone-induced gene regulatory programs in presynaptic neurons. Furthermore, thyroid hormone action in the frontal cortex regulates innate exploratory behaviors and causally promotes exploratory decision-making. Thus, thyroid hormone acts directly on the cerebral cortex in males to coordinate exploratory behaviors with whole-body metabolic state.
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Adolescents are a growing population of people living with HIV. The period between weaning and sexual debut presents a low-risk window for HIV acquisition, making early childhood an ideal time for implementing an immunization regimen. Because the elicitation of broadly neutralizing antibodies (bnAbs) is critical for an effective HIV vaccine, our goal was to assess the ability of a bnAb B cell lineage-designed HIV envelope SOSIP (protein stabilized by a disulfide bond between gp120-gp41-named "SOS"-and an isoleucine-to-proline point mutation-named "IP"-at residue 559) to induce precursor CD4 binding site (CD4bs)-targeting bnAbs in early life. Infant rhesus macaques received either a BG505 SOSIP, based on the infant BG505 transmitted/founder virus, or the CD4bs germ line-targeting BG505 SOSIP GT1.1 (n = 5 per group). Although both strategies induced durable, high-magnitude plasma autologous virus neutralization responses, only GT1.1-immunized infants (n = 3 of 5) exhibited VRC01-like CD4bs bnAb precursor development. Thus, a multidose immunization regimen with bnAb lineage-designed SOSIPs shows promise for inducing early B cell responses with the potential to mature into protective HIV bnAbs before sexual debut.
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Vacinas contra a AIDS , Anticorpos Anti-HIV , Macaca mulatta , Animais , Anticorpos Anti-HIV/imunologia , Vacinas contra a AIDS/imunologia , Vacinas contra a AIDS/administração & dosagem , Anticorpos Neutralizantes/imunologia , Anticorpos Amplamente Neutralizantes/imunologia , Imunização , Produtos do Gene env do Vírus da Imunodeficiência Humana/imunologia , HIV-1/imunologia , Infecções por HIV/imunologia , Infecções por HIV/prevenção & controle , Humanos , Células Germinativas/imunologiaRESUMO
This secondary study examined bullying perpetration's relationships with social disorganization, social structural factors, social relationships, mental health, and access to health insurance and care. A sample of 30,173 children age 6 to 17 years was extracted from the 2021 National Survey of Children's Health for secondary data analysis. Logistic regression results demonstrated that these children's likelihood of bullying perpetration was positively associated with racial discrimination, child age 6 to 10 years, child age 11 to 13 years, parent education level, employed parent, neighbor support, family violence, difficulty parenting the child, child difficulty with peers, child behavioral/conduct problems, family substance use problem, and child receipt of mental health services; such likelihood also had negative associations with safe neighborhood, Black, Asian, other non-Hispanic ethnic minority, parent age, and family cohesiveness. Implications included interventions to promote awareness of racial discrimination for families as well as bully prevention programs in schools and communities.
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Fever elicited by bacterial lypopolyssacharide (LPS) is mediated by pro-inflammatory cytokines, which activate central mediators and regulate the hypothalamic temperature setpoint. This response is often accompanied by morphological changes involving the extracellular matrix, neurons and glial cells, with significant health impacts. The NK1 receptor is involved in the febrile response induced by LPS but its effects over the extracellular matrix in the context of neuroinflammation remain unknown. The present work aims to clarify the extracellular changes associated with NK1 signaling in LPS-induced fever. Male Wistar rats were exposed to LPS intraperitoneally. Experimental groups were pre-treated intracerebroventricularly with the NK1 selective inhibitor SR140333B or saline. Histological changes involving the brain extracellular matrix were evaluated using hematoxylin and eosin, Mason's trichrome, picrosirius, alcian blue, periodic acid Schiff's stains. The expression of matrix metalloproteinase 9 (MMP9) was studied using confocal microscopy. Fever was accompanied by edema, perivascular lymphoplamacytic and neutrophylic infiltration, spongiosis and MMP9 overexpression. SR140333B significantly reduced LPS-induced fever (p < 0.0001), MMP9 overexpression (p < 0.01) and associated histological changes. These results contribute to characterize cerebral extracellular matrix changes associated with LPS-induced fever. Overall, the present work supports a role for NK1 receptor in these neuroinflammatory changes, involving MMP9 overexpression, edema and leukocytic infiltration.
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Febre , Lipopolissacarídeos , Ratos Wistar , Receptores da Neurocinina-1 , Animais , Masculino , Febre/induzido quimicamente , Febre/metabolismo , Lipopolissacarídeos/farmacologia , Ratos , Receptores da Neurocinina-1/metabolismo , Metaloproteinase 9 da Matriz/metabolismo , Encéfalo/metabolismo , Encéfalo/patologia , Encéfalo/efeitos dos fármacos , Matriz Extracelular/metabolismo , Matriz Extracelular/efeitos dos fármacos , Neurônios/metabolismo , Neurônios/patologia , Neurônios/efeitos dos fármacos , Antagonistas dos Receptores de Neurocinina-1/farmacologiaRESUMO
OBJECTIVES: To explore the cost conversations taking place when patients with atrial fibrillation and their clinicians decide on whether and how to use anticoagulation to prevent strokes. METHODS: Secondary qualitative thematic analysis of conversations from 476 clinical encounters in three sites of a multicenter randomized trial comparing usual care with and without a shared decision-making tool. RESULTS: We identified three themes with subthemes: (1) What was discussed: conversation content (2) How content was transmitted: communication patterns and (3) Implicit conversation drivers. Due to each patient's unique circumstances, bi-directional conversations focused on relationship- and solution-based content enabled better cost burden discovery. Conversation drivers included affordability, comorbidities, preferences, and uncertainty about future costs. CONCLUSIONS: Cost conversations were often initiated by clinicians, and if they did not invite a response, patients passively received information without understanding or weighing cost burden. When clinicians discussed cost information using relational or solution-focused content and bi-directional communication patients were more likely to engage in discussion including their unique situation. PRACTICE IMPLICATIONS: Solution-focused cost conversations can reduce financial treatment burden, but require estimates of out-of-pocket costs, insurance coverage, and long-term financial effects of various options. Conversation tools and information on financial resources are valuable to patients and clinicians.
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Anticoagulantes , Fibrilação Atrial , Comunicação , Relações Médico-Paciente , Pesquisa Qualitativa , Humanos , Feminino , Masculino , Anticoagulantes/uso terapêutico , Anticoagulantes/economia , Idoso , Pessoa de Meia-Idade , Tomada de Decisão Compartilhada , Acidente Vascular Cerebral , Tomada de Decisões , Participação do PacienteRESUMO
The basal ganglia (BG) are an evolutionarily conserved and phylogenetically old set of sub-cortical nuclei that guide action selection, evaluation, and reinforcement. The entopeduncular nucleus (EP) is a major BG output nucleus that contains a population of GABA/glutamate cotransmitting neurons (EP Sst+ ) that specifically target the lateral habenula (LHb) and whose function in behavior remains mysterious. Here we use a probabilistic switching task that requires an animal to maintain flexible relationships between action selection and evaluation to examine when and how GABA/glutamate cotransmitting neurons contribute to behavior. We find that EP Sst+ neurons are strongly engaged during this task and show bidirectional changes in activity during the choice and outcome periods of a trial. We then tested the effects of either permanently blocking cotransmission or modifying the GABA/glutamate ratio on behavior in well-trained animals. Neither manipulation produced detectable changes in behavior despite significant changes in synaptic transmission in the LHb, demonstrating that the outputs of these neurons are not required for on-going action-outcome updating in a probabilistic switching task.
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INTRODUCTION: Financial toxicity associated with treatments for metastatic prostate cancer remains poorly defined. We sought to understand aspects of financial toxicity not captured in a commonly employed financial toxicity questionnaire and identify potential interventions to help alleviate financial toxicity through a convergent mixed methods approach. METHODS: Patients seen at our institution's advanced prostate cancer clinic were approached for completion of the Comprehensive Score for Financial Toxicity (COST-FACIT) questionnaire (quantitative analysis). A maximal variation purposive sample was chosen to participate in focus group discussions (qualitative analysis). Conventional content analysis was performed using an inductive approach. COST-FACIT scores were compared between patients experiencing high and low financial toxicity using Wilcoxon rank sum test. RESULTS: Three themes were identified through qualitative analysis: (1) workload, (2) coping strategies, and (3) communication. We found alignment with the existing theory of financial capacity across our findings. Two unique aspects of financial toxicity emerged that were not assessed quantitatively and deemed to be significant. Specifically, cost transparency (including health care teams knowledgeable about and willing to discuss costs) and inclusion of informal caregivers in financial toxicity screening and decision-making may guide future interventions aimed at limiting financial toxicity in this population. CONCLUSIONS: Prolonged treatment courses involving multiple lines of treatment with varying costs result in distinct financial toxicity components for patients with metastatic prostate cancer that are not assessed with COST-FACIT. Improving cost transparency, health care team knowledge and engagement, and providing resources to support informal caregivers may have a significant impact on the financial toxicity experienced by these patients.
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Neoplasias da Próstata , Humanos , Masculino , Neoplasias da Próstata/patologia , Neoplasias da Próstata/economia , Idoso , Pessoa de Meia-Idade , Metástase Neoplásica , Inquéritos e Questionários , Adaptação Psicológica , Grupos Focais , Efeitos Psicossociais da Doença , Carga de TrabalhoRESUMO
Mindfulness witnessed a substantial popularity surge in the past decade, especially as digitally self-administered interventions became available at relatively low costs. Yet, it is uncertain whether they effectively help reduce stress. In a preregistered (OSF https://doi.org/10.17605/OSF.IO/UF4JZ ; retrospective registration at ClinicalTrials.gov NCT06308744 ) multi-site study (nsites = 37, nparticipants = 2,239, 70.4% women, Mage = 22.4, s.d.age = 10.1, all fluent English speakers), we experimentally tested whether four single, standalone mindfulness exercises effectively reduced stress, using Bayesian mixed-effects models. All exercises proved to be more efficacious than the active control. We observed a mean difference of 0.27 (d = -0.56; 95% confidence interval, -0.43 to -0.69) between the control condition (M = 1.95, s.d. = 0.50) and the condition with the largest stress reduction (body scan: M = 1.68, s.d. = 0.46). Our findings suggest that mindfulness may be beneficial for reducing self-reported short-term stress for English speakers from higher-income countries.
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Activation of natural killer (NK) cells with the cytokines interleukin-12 (IL-12), IL-15, and IL-18 induces their differentiation into memory-like (ML) NK cells; however, the underlying epigenetic and transcriptional mechanisms are unclear. By combining ATAC-seq, CITE-seq, and functional analyses, we discovered that IL-12/15/18 activation results in two main human NK fates: reprogramming into enriched memory-like (eML) NK cells or priming into effector conventional NK (effcNK) cells. eML NK cells had distinct transcriptional and epigenetic profiles and enhanced function, whereas effcNK cells resembled cytokine-primed cNK cells. Two transcriptionally discrete subsets of eML NK cells were also identified, eML-1 and eML-2, primarily arising from CD56bright or CD56dim mature NK cell subsets, respectively. Furthermore, these eML subsets were evident weeks after transfer of IL-12/15/18-activated NK cells into patients with cancer. Our findings demonstrate that NK cell activation with IL-12/15/18 results in previously unappreciated diverse cellular fates and identifies new strategies to enhance NK therapies.
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Citocinas , Epigênese Genética , Memória Imunológica , Células Matadoras Naturais , Humanos , Células Matadoras Naturais/imunologia , Epigênese Genética/imunologia , Memória Imunológica/imunologia , Citocinas/imunologia , Regulação da Expressão Gênica/imunologia , Diferenciação Celular/imunologia , Interleucina-15/imunologiaRESUMO
Identifying immune correlates of protection is a major challenge in AIDS vaccine development. Anti-Envelope antibodies have been considered critical for protection against SIV/HIV (SHIV) acquisition. Here, we evaluated the efficacy of an SHIV vaccine against SIVmac251 challenge, where the role of antibody was excluded, as there was no cross-reactivity between SIV and SHIV envelope antibodies. After 8 low-dose intrarectal challenges with SIVmac251, 12 SHIV-vaccinated animals demonstrated efficacy, compared with 6 naive controls, suggesting protection was achieved in the absence of anti-envelope antibodies. Interestingly, CD8+ T cells (and some NK cells) were not essential for preventing viral acquisition, as none of the CD8-depleted macaques were infected by SIVmac251 challenges. Initial investigation of protective innate immunity revealed that protected animals had elevated pathways related to platelet aggregation/activation and reduced pathways related to interferon and responses to virus. Moreover, higher expression of platelet factor 4 on circulating platelet-leukocyte aggregates was associated with reduced viral acquisition. Our data highlighted the importance of innate immunity, identified mechanisms, and may provide opportunities for novel HIV vaccines or therapeutic strategy development.
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Linfócitos T CD8-Positivos , Imunidade Inata , Macaca mulatta , Vacinas contra a SAIDS , Síndrome de Imunodeficiência Adquirida dos Símios , Vírus da Imunodeficiência Símia , Animais , Síndrome de Imunodeficiência Adquirida dos Símios/imunologia , Síndrome de Imunodeficiência Adquirida dos Símios/prevenção & controle , Vírus da Imunodeficiência Símia/imunologia , Vacinas contra a SAIDS/imunologia , Imunidade Inata/imunologia , Linfócitos T CD8-Positivos/imunologia , Anticorpos Antivirais/imunologia , Masculino , Vacinas Atenuadas/imunologiaRESUMO
Wildfire activity is increasing globally. The resulting smoke plumes can travel hundreds to thousands of kilometers, reflecting or scattering sunlight and depositing particles within ecosystems. Several key physical, chemical, and biological processes in lakes are controlled by factors affected by smoke. The spatial and temporal scales of lake exposure to smoke are extensive and under-recognized. We introduce the concept of the lake smoke-day, or the number of days any given lake is exposed to smoke in any given fire season, and quantify the total lake smoke-day exposure in North America from 2019 to 2021. Because smoke can be transported at continental to intercontinental scales, even regions that may not typically experience direct burning of landscapes by wildfire are at risk of smoke exposure. We found that 99.3% of North America was covered by smoke, affecting a total of 1,333,687 lakes ≥10 ha. An incredible 98.9% of lakes experienced at least 10 smoke-days a year, with 89.6% of lakes receiving over 30 lake smoke-days, and lakes in some regions experiencing up to 4 months of cumulative smoke-days. Herein we review the mechanisms through which smoke and ash can affect lakes by altering the amount and spectral composition of incoming solar radiation and depositing carbon, nutrients, or toxic compounds that could alter chemical conditions and impact biota. We develop a conceptual framework that synthesizes known and theoretical impacts of smoke on lakes to guide future research. Finally, we identify emerging research priorities that can help us better understand how lakes will be affected by smoke as wildfire activity increases due to climate change and other anthropogenic activities.
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Ecossistema , Lagos , Fumaça , Incêndios Florestais , Fumaça/análise , América do Norte , Monitoramento AmbientalRESUMO
Metastatic (m) colorectal cancer (CRC) is an incurable disease with a poor prognosis and thus remains an unmet clinical need. Immune checkpoint blockade (ICB)-based immunotherapy is effective for mismatch repair-deficient (dMMR)/microsatellite instability-high (MSI-H) mCRC patients, but it does not benefit the majority of mCRC patients. NK cells are innate lymphoid cells with potent effector responses against a variety of tumor cells but are frequently dysfunctional in cancer patients. Memory-like (ML) NK cells differentiated after IL-12/IL-15/IL-18 activation overcome many challenges to effective NK cell anti-tumor responses, exhibiting enhanced recognition, function, and in vivo persistence. We hypothesized that ML differentiation enhances the NK cell responses to CRC. Compared to conventional (c) NK cells, ML NK cells displayed increased IFN-γ production against both CRC cell lines and primary patient-derived CRC spheroids. ML NK cells also exhibited improved killing of CRC target cells in vitro in short-term and sustained cytotoxicity assays, as well as in vivo in NSG mice. Mechanistically, enhanced ML NK cell responses were dependent on the activating receptor NKG2D as its blockade significantly decreased ML NK cell functions. Compared to cNK cells, ML NK cells exhibited greater antibody-dependent cytotoxicity when targeted against CRC by cetuximab. ML NK cells from healthy donors and mCRC patients exhibited increased anti-CRC responses. Collectively, our findings demonstrate that ML NK cells exhibit enhanced responses against CRC targets, warranting further investigation in clinical trials for mCRC patients, including those who have failed ICB.
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Diferenciação Celular , Neoplasias Colorretais , Memória Imunológica , Células Matadoras Naturais , Neoplasias Colorretais/imunologia , Neoplasias Colorretais/patologia , Neoplasias Colorretais/tratamento farmacológico , Células Matadoras Naturais/imunologia , Células Matadoras Naturais/efeitos dos fármacos , Humanos , Animais , Camundongos , Diferenciação Celular/efeitos dos fármacos , Linhagem Celular Tumoral , Interferon gama/metabolismo , Subfamília K de Receptores Semelhantes a Lectina de Células NK/metabolismo , Camundongos Endogâmicos NOD , FemininoRESUMO
The surface receptor CD8α is present on 20%-80% of human (but not mouse) NK cells, yet its function on NK cells remains poorly understood. CD8α expression on donor NK cells was associated with a lack of therapeutic responses in patients with leukemia in prior studies, thus, we hypothesized that CD8α may affect critical NK cell functions. Here, we discovered that CD8α- NK cells had improved control of leukemia in xenograft models compared with CD8α+ NK cells, likely due to an enhanced capacity for proliferation. Unexpectedly, we found that CD8α expression was induced on approximately 30% of previously CD8α- NK cells following IL-15 stimulation. These induced CD8α+ (iCD8α+) NK cells had the greatest proliferation, responses to IL-15 signaling, and metabolic activity compared with those that sustained existing CD8α expression (sustained CD8α+) or those that remained CD8α- (persistent CD8α-). These iCD8α+ cells originated from an IL-15Rßhi NK cell population, with CD8α expression dependent on the transcription factor RUNX3. Moreover, CD8A CRISPR/Cas9 deletion resulted in enhanced responses through the activating receptor NKp30, possibly by modulating KIR inhibitory function. Thus, CD8α status identified human NK cell capacity for IL-15-induced proliferation and metabolism in a time-dependent fashion, and its presence had a suppressive effect on NK cell-activating receptors.
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Antígenos CD8 , Proliferação de Células , Interleucina-15 , Células Matadoras Naturais , Ativação Linfocitária , Humanos , Antígenos CD8/metabolismo , Antígenos CD8/imunologia , Antígenos CD8/genética , Interleucina-15/imunologia , Interleucina-15/metabolismo , Interleucina-15/genética , Células Matadoras Naturais/imunologia , Células Matadoras Naturais/metabolismoRESUMO
Microorganisms can play an important role in food production, especially through fermentation processes [...].
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This study is the first to examine factors in the utilization of physician services, dentist services, hospital care, and prescribed medications focusing exclusively on insured children in the United States. Data describing 48,660 insured children were extracted from the 2021 National Survey of Children's Health. Children in the present sample were covered by private health insurance, public health insurance, or other health insurance. Logistic regression results showed self-reported health to be negatively associated with physician visits, hospital-care use, and prescription use, but teeth condition to be positively associated with dentist visits. Physician visits were associated negatively with age, Hispanic ethnicity, Asian ethnicity, family income at or below 200% of the federal poverty level, and other health insurance, but positively with parental education and metropolitan residency. Dentist visits were associated positively with girls, age, and parental education, but negatively with Asian ethnicity and public health insurance. Use of hospital care was associated negatively with age and Asian ethnicity, but positively with parental education and public health insurance. Use of prescriptions was associated positively with age, Black ethnicity, parental education, and public health insurance, but negatively with Hispanic ethnicity, Asian ethnicity, and family income at or below 200% of the federal poverty level. Implications included the expansion of public health insurance, promotion of awareness of medicine discount programs, and understanding of racial/ethnic minorities' cultural beliefs in health and treatment.
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Seguro Saúde , Humanos , Criança , Feminino , Estados Unidos , Masculino , Pré-Escolar , Lactente , Adolescente , Seguro Saúde/estatística & dados numéricos , Recém-Nascido , Medicamentos sob Prescrição/uso terapêuticoRESUMO
Agricultural practises such as conventional and organic farming can potentially affect the microbial communities in milk. In the present study, the bacterial diversity of milk was investigated using high-throughput sequencing on ten organic and ten conventional farms in the Azores, a region where milk production is largely based on year-round grazing systems. The microbiota of milk from both production systems was dominated by Bacillota, Pseudomonadota, Actinomycetota and Bacteroidota. The organic milk showed greater heterogeneity between farms, as reflected in the dispersion of diversity indices and the large variation in the relative abundances of the dominant genera. In contrast, conventionally produced milk showed a high degree of similarity within each season. In the conventional production system, the season also had a strong influence on the bacterial community, but this effect was not observed in the organic milk. The LEfSe analysis identified the genus Iamia as significantly (p < 0.05) more abundant in organic milk, but depending on the season, several other genera were identified that distinguished organic milk from conventionally produced milk. Of these, Bacillus, Iamia and Nocardioides were associated with the soil microbiota in organic farming.
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Bactérias , Leite , Animais , Bovinos , Feminino , Leite/microbiologia , Bactérias/genética , Agricultura Orgânica , Agricultura , FazendasRESUMO
Background: Microendemic species are species with very small geographic distributions (ranges). Their presence delimitates areas with microendemic species (AMs), denoting a spatial unit comprising at least one population of at least one microendemic species. AMs are assumed to be distributed distinctively and associated with specific ecological, historical, and anthropogenic attributes. However, the level of influence of these factors remains unclear. Thus, we studied the distribution patterns of microendemic species within the Brazilian Atlantic Forest to (a) identify the region's AMs; (b) evaluate whether ecological (latitude, altitude, distance from the coastline), historical (climate stability), and anthropogenic (ecological integrity) attributes distinguish AMs from non-AMs; and (c) assess the conservation status of the Atlantic Forest's AMs. Methods: We mapped the ranges of 1,362 microendemic species of angiosperms, freshwater fishes, and terrestrial vertebrates (snakes, passerine birds, and small mammals) to identify the region's AMs. Further, spatial autoregressive logit regression models were used to evaluate whether latitude, altitude, distance from the coastline, Climate Stability Index, and ecological integrity can be used to discern AMs from non-AMs. Moreover, the AMs' conservation status was assessed by evaluating the region's ecological integrity and conservation efforts (measured as the proportion of AMs in protected areas). Results: We identified 261 AMs for angiosperm, 205 AMs for freshwater fishes, and 102 AMs for terrestrial vertebrates in the Brazilian Atlantic Forest, totaling 474 AMs covering 23.8% of the region. The Brazilian Atlantic Forest is a large and complex biogeographic mosaic where AMs represent islands or archipelagoes surrounded by transition areas with no microendemic species. All local attributes help to distinguish AMs from non-AMs, but their impacts vary across taxonomic groups. Around 69% of AMs have low ecological integrity and poor conservation efforts, indicating that most microendemic species are under threat. This study provides insights into the biogeography of one of the most important global biodiversity hotspots, creating a foundation for comparative studies using other tropical forest regions.
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Biodiversidade , Magnoliopsida , Animais , Florestas , Vertebrados , Clima , Brasil , MamíferosRESUMO
Drier and hotter conditions linked with anthropogenic climate change can increase wildfire frequency and severity, influencing terrestrial and aquatic carbon cycles at broad spatial and temporal scales. The impacts of wildfire are complex and dependent on several factors that may increase terrestrial deposition and the influx of dissolved organic matter (DOM) from plants into nearby aquatic systems, resulting in the darkening of water color. We tested the effects of plant biomass quantity and its interaction with fire (burned vs. unburned plant biomass) on dissolved organic carbon (DOC) concentration and degradation (biological vs. photochemical) and DOM composition in 400 L freshwater ponds using a gradient experimental design. DOC concentration increased nonlinearly with plant biomass loading in both treatments, with overall higher concentrations (>56 mg/L) in the unburned treatment shortly after plant addition. We also observed nonlinear trends in fluorescence and UV-visible absorbance spectroscopic indices as a function of fire treatment and plant biomass, such as greater humification and specific UV absorbance at 254 nm (a proxy for aromatic DOM) over time. DOM humification occurred gradually over time with less humification in the burned treatment compared to the unburned treatment. Both burned and unburned biomass released noncolored, low molecular weight carbon compounds that were rapidly consumed by microbes. DOC decomposition exhibited a unimodal relationship with plant biomass, with microbes contributing more to DOC loss than photodegradation at intermediate biomass levels (100-300 g). Our findings demonstrate that the quantity of plant biomass leads to nonlinear responses in the dynamics and composition of DOM in experimental ponds that are altered by fire, indicating how disturbances interactively affect DOM processing and its role in aquatic environments.