Dams contribute to water security, energy supply, and flood protection but also fragment habitats of freshwater species. Yet, a global species-level assessment of dam-induced fragmentation is ...lacking. Here, we assessed the degree of fragmentation of the occurrence ranges of ∼10,000 lotic fish species worldwide due to ∼40,000 existing large dams and ∼3,700 additional future large hydropower dams. Per river basin, we quantified a connectivity index (CI) for each fish species by combining its occurrence range with a high-resolution hydrography and the locations of the dams. Ranges of nondiadromous fish species were more fragmented (less connected) (CI = 73 ± 28%; mean ± SD) than ranges of diadromous species (CI = 86 ± 19%). Current levels of fragmentation were highest in the United States, Europe, South Africa, India, and China. Increases in fragmentation due to future dams were especially high in the tropics, with declines in CI of ∼20 to 40 percentage points on average across the species in the Amazon, Niger, Congo, Salween, and Mekong basins. Our assessment can guide river management at multiple scales and in various domains, including strategic hydropower planning, identification of species and basins at risk, and prioritization of restoration measures, such as dam removal and construction of fish bypasses.
Secondary organic aerosols (SOA) are large contributors to fine‐particle loadings and radiative forcing but are often represented crudely in global models. We have implemented three new detailed SOA ...treatments within the Community Atmosphere Model version 5 (CAM5) that allow us to compare the semivolatile versus nonvolatile SOA treatments (based on some of the latest experimental findings) and to investigate the effects of gas‐phase fragmentation reactions. The new treatments also track SOA from biomass burning and biofuel, fossil fuel, and biogenic sources. For semivolatile SOA treatments, fragmentation reactions decrease the simulated annual global SOA burden from 7.5 Tg to 1.8 Tg. For the nonvolatile SOA treatment with fragmentation, the burden is 3.1 Tg. Larger differences between nonvolatile and semivolatile SOA (up to a factor of 5) exist in areas of continental outflow over the oceans. According to comparisons with observations from global surface Aerosol Mass Spectrometer measurements and the U.S. Interagency Monitoring of Protected Visual Environments (IMPROVE) network measurements, the FragNVSOA treatment, which treats SOA as nonvolatile and includes gas‐phase fragmentation reactions, agrees best at rural locations. Urban SOA is underpredicted, but this may be due to the coarse model resolution. All three revised treatments show much better agreement with aircraft measurements of organic aerosols (OA) over the North American Arctic and sub‐Arctic in spring and summer, compared to the standard CAM5 formulation. This is mainly due to the oxidation of SOA precursor gases from biomass burning, not included in standard CAM5, and long‐range transport of biomass burning OA at high altitudes. The revised model configurations that include fragmentation (both semivolatile and nonvolatile SOA) show much better agreement with MODerate resolution Imaging Spectrometers (MODIS) aerosol optical depth data over regions dominated by biomass burning during the summer compared to standard CAM5, and predict biomass burning and biofuel as the largest global source of OA, followed by biogenic and fossil fuel sources. The large contribution of biomass burning OA in the revised treatments is supported by these measurements, but the emissions and aging of SOA precursors and POA are uncertain, and need further investigation. The nonvolatile and semivolatile configurations with fragmentation predict the direct radiative forcing of SOA as −0.5 W m−2 and −0.26 W m−2 respectively, at top of the atmosphere, which are higher than previously estimated by most models, but in reasonable agreement with a recent constrained modeling study. This study highlights the importance of improving process‐level representation of SOA in global models.
Key Points
Fragmentation is an important sink of SOA
Biomass burning is the largest SOA source
SOA DRF is higher than most models
Aim
While habitat loss is a primary driver of biodiversity declines worldwide, the role of habitat fragmentation per se is inconclusive, but likely depends on the amount of habitat left in a ...landscape. Here we aimed to tease apart the effects of habitat amount (percentage of native cover) and a fragmentation metric (number of fragments) on species richness and total abundance.
Taxon
Native small mammals.
Location
South American Atlantic Forest biome.
Methods
Small mammal species richness and abundance were obtained from a published database for 96 localities (groups of sampling sites). We then defined circular 100 km2 landscapes centred on each locality. For each landscape, percentage of habitat cover and number of fragments were measured on time frames close to the sampling periods. Effects of habitat amount, fragmentation and their interaction were modelled considering all landscapes, and also within four classes of habitat cover: 0%–10%, 10%–30%, 30%–50%, and 50%–100%.
Results
Species richness was mainly affected by percentage of habitat cover, with a three‐fold effect size compared to fragmentation. Yet, in landscapes with <10% or ≥50% of remaining cover, fragmentation positively affected species richness. Total species abundance also increased towards more fragmented landscapes. At the species level, three of the 20 species considered increased in abundance with fragmentation, while four species decreased.
Main conclusion
Percentage of habitat cover was the main driver of species richness when the entire cover range is considered, but the secondary effects of fragmentation were strong at the extreme ends of this range. Adding habitat patches in landscapes with low cover, or promoting habitat heterogeneity in landscapes with high cover, may boost species richness. However, further increases in species richness following fragmentation in high‐cover landscapes are likely to correspond to disturbance‐adapted species. In addition, such positive effects of fragmentation cannot be presumed to apply to all assemblages and species as some species are negatively affected.
Rapid urban expansion has profound impacts on global biodiversity through habitat conversion, degradation, fragmentation, and species extinction. However, how future urban expansion will affect ...global biodiversity needs to be better understood. We contribute to filling this knowledge gap by combining spatially explicit projections of urban expansion under shared socioeconomic pathways (SSPs) with datasets on habitat and terrestrial biodiversity (amphibians, mammals, and birds). Overall, future urban expansion will lead to 11-33 million hectares of natural habitat loss by 2100 under the SSP scenarios and will disproportionately cause large natural habitat fragmentation. The urban expansion within the current key biodiversity priority areas is projected to be higher (e.g., 37-44% higher in the WWF's Global 200) than the global average. Moreover, the urban land conversion will reduce local within-site species richness by 34% and species abundance by 52% per 1 km grid cell, and 7-9 species may be lost per 10 km cell. Our study suggests an urgent need to develop a sustainable urban development pathway to balance urban expansion and biodiversity conservation.
Glyphosate is the active ingredient of Roundup
, which is one of the most popular herbicides worldwide. Although many studies have focused on the reproductive toxicity of glyphosate or ...glyphosate-based herbicides, the majority of them have concluded that the effect of the specific herbicide is negligible, while only a few studies indicate the male reproductive toxicity of glyphosate alone. The aim of the present study was to investigate the effect of 0.36 mg/L glyphosate on sperm motility and sperm DNA fragmentation (SDF). Thirty healthy men volunteered to undergo semen analysis for the purpose of the study. Sperm motility was calculated according to WHO 2010 guidelines at collection time (zero time) and 1 h post-treatment with glyphosate. Sperm DNA fragmentation was evaluated with Halosperm
G2 kit for both the control and glyphosate-treated sperm samples. Sperm progressive motility of glyphosate-treated samples was significantly reduced after 1 h post-treatment in comparison to the respective controls, in contrast to the SDF of glyphosate-treated samples, which was comparable to the respective controls. Conclusively, under these in vitro conditions, at high concentrations that greatly exceed environmental exposures, glyphosate exerts toxic effects on sperm progressive motility but not on sperm DNA integrity, meaning that the toxic effect is limited only to motility, at least in the first hour.
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•Dolomite primary fragmentation in a pressurized TG was investigated.•Increase of pressure and PH2O is effective in preventing fragmentation.•Primary fragmentation mechanisms in high ...pressure and high PH2O were proposed.•Dolomite as bed material in a pressurized FB gasifier were tested.•Implications for pressurized FB gasification are discussed.
Dolomite shows superior tar cracking and anti-agglomeration abilities in gasification processes, while its fragmentation at elevated temperatures is still a major obstacle inhibiting its applications in fluidized bed (FB) applications. To improve the understanding of its performance in pressurized FB gasification, we investigated fragmentation behaviors of crystalline Glanshammar and amorphous Sala dolomite at both isothermal and non-isothermal modes under pressurized H2O and CO2 conditions. A series of tests under various conditions, i.e. pressure, temperature, heating rate, gas atmosphere, and dolomite types, was conducted. The primary fragmentation of Glanshammar is significantly reduced at 10 bar. Dolomite exposed to a PH2O of 10 bar has the lowest fragmentation among all cases. Both dolomites were also loaded into a pressurized fluidized bed gasifier as bed material. Glanshammar exhibits approximately 14% loss of its initial mass of bed, a much higher loss compared to the Sala dolomite with only 5.5%. Fragmentation mechanisms at pressurized conditions in the presence of H2O and CO2 and measures to mitigate dolomite fragmentation in pressurized FB gasifiers are proposed. During gasification, both high operating pressure and high PH2O are beneficial for fragmentation mitigation. To mitigate an initial fragmentation of dolomite during the reactor heating-up stage, a pressurization to the operating pressure before reaching the initial fragmentation temperature of dolomite (400 °C) is recommended. Crystalline dolomite, is the preferred choice, if a pretreatment at a high-pressure using H2O is applied.
The Good and the Bad of Mitochondrial Breakups Sprenger, Hans-Georg; Langer, Thomas
Trends in cell biology,
November 2019, 2019-11-00, 20191101, Letnik:
29, Številka:
11
Journal Article
Recenzirano
Mitochondrial morphology is a crucial determinant of mitochondrial and cellular function. Opposing fusion and fission events shape the tubular mitochondrial reticulum and ensure mitochondrial ...transport within cells. Cellular stress and pathophysiological conditions can lead to fragmentation of the mitochondrial network, which facilitates mitophagy and is associated with cell death. However, mitochondrial shape changes are also intertwined with the cellular metabolism, and metabolic switches can induce but also result from alterations in mitochondrial morphology. Here, we discuss recent advances in the field of mitochondrial dynamics, demonstrating cell- and tissue-specific effects of mitochondrial fragmentation on cellular metabolism, cell survival, and mitochondrial quality control.
Mitochondria constantly undergo fusion and fission events and form dynamic tubular and interconnected networks within cells.Mitochondrial fragmentation is induced by stress and metabolic cues and occurs during ageing and in disease.Transient mitochondrial fragmentation facilitates mitophagy, while chronic fragmentation is associated with cell death.The physiological consequences of mitochondrial fragmentation are cell-type and tissue specific.Pleiotropic functions of key players in fusion and fission machineries and various metabolic profiles of the cells may determine the outcome of mitochondrial fragmentation.
Objective To review the mechanisms responsible for DNA fragmentation in human sperm, including those occurring during spermatogenesis and transport through the reproductive tract. The mechanisms ...examined include: apoptosis in the seminiferous tubule epithelium, defects in chromatin remodeling during the process of spermiogenesis, oxygen radical-induced DNA damage during sperm migration from the seminiferous tubules to the epididymis, the activation of sperm caspases and endonucleases, damage induced by chemotherapy and radiotherapy, and the effect of environmental toxicants. The different tests currently used for sperm DNA fragmentation analysis and the factors that determine the predictive value of sperm DNA fragmentation testing and their implications in the diagnosis and treatment of infertility are also discussed. Finally, we also scrutinize how the presence in the embryonic genome of DNA strand breaks or modifications of DNA nucleotides inherited from the paternal genome could impact the embryo and offspring. In particular we discuss how abnormal sperm could be dealt with by the oocyte and how sperm DNA abnormalities, which have not been satisfactorily repaired by the oocyte after fertilization, may interfere with normal embryo and fetal development. Conclusion(s) Sperm DNA can be modified through various mechanisms. The integrity of the paternal genome is therefore of paramount importance in the initiation and maintenance of a viable pregnancy both in a natural conception and in assisted reproduction. The need to diagnose sperm at a nuclear level is an area that needs further understanding so that we can improve treatment of the infertile couple.
Habitat loss and fragmentation are among the biggest threats to biodiversity. Anthropogenic habitat fragmentation leads to small and isolated remnant plant and animal populations. The combination of ...increased random genetic drift, inbreeding, and reduced gene flow may substantially reduce genetic variation of remnant populations. However, the magnitude of these responses may depend on several poorly understood factors including organism group, habitat type of both the fragment and the surrounding matrix, life‐history traits, and time since fragmentation. We compiled data for 83 plant and 52 animal species and conducted a meta‐analysis following best practices to evaluate how these factors mediate the effects of anthropogenic habitat fragmentation. We calculated 206 effect sizes as correlations between one of four measures of population‐level genetic diversity and fragment area. All analyses were repeated using models of increasing complexity (traditional random‐effects models, multilevel models accounting for non‐independent data, and multilevel models additionally correcting for phylogenetic relatedness). We confirmed that anthropogenic habitat fragmentation has overall negative effects on genetic diversity of organisms. Our meta‐analysis shows, however, that plant species responded in general stronger to fragmentation than animal species and that the largest negative impacts of fragmentation occurred in tropical and temperate forest fragments, surrounded by a non‐forest matrix. In contrast, we found only weak responses in non‐forest fragments. Genetic diversity measured as mean number of alleles (A) showed the strongest response to fragmentation. Expected heterozygosity (He) and percentage of polymorphic loci (PLP) showed similar but weaker responses. In contrast, our meta‐analysis indicated that inbreeding (Fis) was not measurably affected by anthropogenic habitat fragmentation. Additionally, our models revealed that effects on genetic diversity became stronger with age of fragments: We found significant negative responses for fragments older than 50 yr but not for those more recently isolated. Our meta‐analyses also showed that currently animals are underrepresented in the literature on genetic effects of anthropogenic fragmentation, as are certain geographical regions and habitat types. We expect that future field studies using state‐of‐the‐art approaches will provide further evidence of negative genetic effects, which may reinforce the here reported patterns, even for groups not yet studied.
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