QUESTIONS: Soil properties have been shown to partially explain tree species distribution in tropical forests. Locally, species turnover across space can result not only from edaphic heterogeneities ...but also from limited seed dispersal. To characterize the contribution of each process, contact areas between contrasted soil types offer ideal settings. In the present study, we aimed to test species and species assemblage responses to a sharp edaphic discontinuity in a tropical forest tree community. LOCATION: Yoko forest reserve (6975 ha), Democratic Republic of the Congo. METHODS: We set up four 500–600‐m long parallel transects crossing two contrasted edaphic habitats, one lying on clayey soil and the other on sandy soil. The canopy and subcanopy trees were identified and geo‐referenced along the transects over a width of 50 m and 5 m, respectively, and soil samples were collected every 50 m to characterize each habitat. RESULTS: Correspondence analyses indicated a clear differentiation of tree communities between sandy and clayey soils. Using a torus‐translation method combined with Chi‐squared non‐parametric tests, we observed that ca. 40% and 18% of the species represented by at least 12 individuals displayed significant density differences according to habitat in the canopy and subcanopy, respectively, although very few species displayed significant differences in their relative abundance. Nevertheless, whole community tests of differentiation (in species relative abundances) between soil types were significant in both strata, even after removing individual species or families displaying a significant habitat preference. CONCLUSION: While only a minority of species displayed a clear habitat preference, we still observed a community‐wide impact of the edaphic discontinuity on species assemblages at a local scale. Our results provide further evidence for the major contribution of environmental heterogeneity in maintaining biodiversity in tropical forests.
Ataxia oculomotor apraxia type 2 (AOA2) is a rare autosomal recessive cerebellar ataxia. Recent evidence suggests that the protein defective in this syndrome, senataxin (SETX), functions in RNA ...processing to protect the integrity of the genome. To date, only patient-derived lymphoblastoid cells, fibroblasts and SETX knockdown cells were available to investigate AOA2. Recent disruption of the Setx gene in mice did not lead to neurobehavioral defects or neurodegeneration, making it difficult to study the etiology of AOA2. To develop a more relevant neuronal model to study neurodegeneration in AOA2, we derived neural progenitors from a patient with AOA2 and a control by induced pluripotent stem cell (iPSC) reprogramming of fibroblasts. AOA2 iPSC and neural progenitors exhibit increased levels of oxidative damage, DNA double-strand breaks, increased DNA damage-induced cell death and R-loop accumulation. Genome-wide expression and weighted gene co-expression network analysis in these neural progenitors identified both previously reported and novel affected genes and cellular pathways associated with senataxin dysfunction and the pathophysiology of AOA2, providing further insight into the role of senataxin in regulating gene expression on a genome-wide scale. These data show that iPSCs can be generated from patients with the autosomal recessive ataxia, AOA2, differentiated into neurons, and that both cell types recapitulate the AOA2 cellular phenotype. This represents a novel and appropriate model system to investigate neurodegeneration in this syndrome.
Calculation of electromagnetic cross sections from surface integral equation simulations, a popular approach in microwave studies and recently also in optics and plasmonics, requires only a single ...post-processing step, which can, however, be very sensitive to the precision of the simulation result. We investigate the accuracy and robustness of two methods for cross section calculation, displaying when and why errors may occur, in certain cases even unphysical behavior. A calculation recipe which avoids unphysical results is given, ensuring convergence of all obtained cross sections. This study will help judge the accuracy of performed simulations and can prevent misinterpretation of modeling results.
Since the discovery of RNA interference (RNAi) in the nematode worm
Caenorhabditis elegans
in 1998 by Fire and Mello et al., strides have been made in exploiting RNAi for therapeutic applications and ...more recently for highly selective insect pest control. Although triggering mRNA degradation in insects through RNAi offers significant opportunities in crop protection, the application of environmental naked dsRNA is often ineffective in eliciting a RNAi response that results in pest lethality. There are many possible reasons for the failed or weak induction of RNAi, with predominant causes being the degradation of dsRNA in the formulated pesticide, in the field or in the insect once ingested, poor cuticular and oral uptake of the nucleic acid and sometimes the lack of an innate strong systemic RNAi response. Therefore, in the last 10 years significant research effort has focused on developing methods for the protection and delivery of environmental dsRNA to enable RNAi-induced insect control. This review focuses on the design and synthesis of vectors (vehicles that are capable of carrying and protecting dsRNA) that successfully enhance mRNA degradation via the RNAi machinery. The majority of solutions exploit the ability of charged polymers, both synthetic and natural, to complex with dsRNA, but alternative nanocarriers such as clay nanosheets and liposomal vesicles have also been developed. The various challenges of dsRNA delivery and the obstacles in the development of well-designed nanoparticles that act to protect the nucleic acid are highlighted. In addition, future research directions for improving the efficacy of RNA-mediated crop protection are anticipated with inspiration taken from polymeric architectures constructed for RNA-based therapeutic applications.
Riverine iron (Fe) derived from glacial weathering is a critical micronutrient source to ecosystems of the Gulf of Alaska (GoA). Here we demonstrate that the source and chemical nature of riverine Fe ...input to the GoA could change dramatically due to the widespread watershed deglaciation that is underway. We examine Fe size partitioning, speciation, and isotopic composition in tributaries of the Copper River which exemplify a long‐term GoA watershed evolution from one strongly influenced by glacial weathering to a boreal‐forested watershed. Iron fluxes from glacierized tributaries bear high suspended sediment and colloidal Fe loads of mixed valence silicate species, with low concentrations of dissolved Fe and dissolved organic carbon (DOC). Iron isotopic composition is indicative of mechanical weathering as the Fe source. Conversely, Fe fluxes from boreal‐forested systems have higher dissolved Fe concentrations corresponding to higher DOC concentrations. Iron colloids and suspended sediment consist of Fe (hydr)oxides and organic complexes. These watersheds have an iron isotopic composition indicative of an internal chemical processing source. We predict that as the GoA watershed evolves due to deglaciation, so will the source, flux, and chemical nature of riverine Fe loads, which could have significant ramifications for Alaskan marine and freshwater ecosystems.
Key Points
Iron colloidal and particulate speciation in glacierized rivers is unique
As glaciers disappear, the flux and chemistry of riverine iron will change
These changes are associated with the source of riverine iron
The natural regeneration of tree species depends on seed and pollen dispersal. To assess whether limited dispersal could be critical for the sustainability of selective logging practices, we ...performed parentage analyses in two Central African legume canopy species displaying contrasted floral and fruit traits: Distemonanthus benthamianus and Erythrophleum suaveolens. We also developed new tools linking forward dispersal kernels with backward migration rates to better characterize long‐distance dispersal. Much longer pollen dispersal in D. benthamianus (mean distance dp = 700 m, mp = 52% immigration rate in 6 km2 plot, s = 7% selfing rate) than in E. suaveolens (dp = 294 m, mp = 22% in 2 km2 plot, s = 20%) might reflect different insect pollinators. At a local scale, secondary seed dispersal by vertebrates led to larger seed dispersal distances in the barochorous E. suaveolens (ds = 175 m) than in the wind‐dispersed D. benthamianus (ds = 71 m). Yet, seed dispersal appeared much more fat‐tailed in the latter species (15%–25% seeds dispersing >500 m), putatively due to storm winds (papery pods). The reproductive success was correlated to trunk diameter in E. suaveolens and crown dominance in D. benthamianus. Contrary to D. benthamianus, E. suaveolens underwent significant assortative mating, increasing further the already high inbreeding of its juveniles due to selfing, which seems offset by strong inbreeding depression. To achieve sustainable exploitation, seed and pollen dispersal distances did not appear limiting, but the natural regeneration of E. suaveolens might become insufficient if all trees above the minimum legal cutting diameter were exploited. This highlights the importance of assessing the diameter structure of reproductive trees for logged species.
Few clinical trials address efficacy of adjuvant systemic treatment in patients with in‐transit melanoma (ITM). This study describes adjuvant systemic therapy of ITM patients beyond clinical trials. ...In this study, we included stage III adjuvant‐treated melanoma patients registered in the nationwide Dutch Melanoma Treatment Registry between July 2018 and December 2020. Patients were divided into three groups: nodal disease only, ITM only and ITM and nodal disease. Recurrence patterns, recurrence‐free survival (RFS) and overall survival (OS) at 12‐months were analyzed. In our study population of 1037 patients, 66.8% had nodal disease only, 16.7% had ITM only and 16.2% had ITM with nodal disease. RFS at 12‐months was comparable in the nodal only and ITM only group (72.2% vs70.1%, P = .97) but lower in ITM and nodal disease patients (57.8%; P = .01, P < .01). Locoregional metastases occurred as first recurrence in 38.9% nodal disease only, 71.9% of ITM‐only and 44.0% of ITM and nodal disease patients. Distant recurrences occurred in 42.3%, 18.8% and 36.0%, respectively (P = .02). 12‐months OS was not significantly different for nodal disease only patients compared with ITM‐only (94.4% vs 97.6%, P = .06) but was significantly higher for ITM‐only compared with ITM and nodal disease patients (97.6% vs 91.0%, P < .01). In conclusion, we showed that in the adjuvant setting, RFS rates in ITM‐only patients are similar to non‐ITM, though better than in ITM and nodal disease patients. Adjuvant‐treated ITM‐only patients less often experience distant recurrences and have a superior OS compared with ITM and nodal disease patients.
What's new?
In some melanoma cases, metastases arise between the primary tumor site and the first draining regional lymph node, called in‐transit melanoma (ITM). Here, the authors investigated the efficacy of adjuvant treatment for ITM. In patients with stage III, adjuvant‐treated melanoma, recurrence‐free survival after 12 months was comparable between patients with nodal disease only and those with ITM only, but shorter in patients with both. This is the first large cohort study on adjuvant‐treated ITM, and the results suggest that nodal status could indicate different treatment strategies for ITM patients.
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