Unicellular nitrogen fixer Crocosphaera contributes substantially to nitrogen fixation in oligotrophic subtropical gyres. They fix nitrogen even when significant amounts of ammonium are available. This has been puzzling since fixing nitrogen is energetically inefficient compared with using available ammonium. Here we show that by fixing nitrogen, Crocosphaera can increase their population and expand their niche despite the presence of ammonium. We have developed a simple but mechanistic model of Crocosphaera based on their growth in steady state culture. The model shows that the growth of Crocosphaera can become nitrogen limited despite their capability to fix nitrogen. When they fix nitrogen, the population increases by up to 78% relative to the case without nitrogen fixation. When we simulate a simple ecological situation where Crocosphaera exists with non-nitrogen-fixing phytoplankton, the relative abundance of Crocosphaera increases with nitrogen fixation, while the population of non-nitrogen-fixing phytoplankton decreases since a larger fraction of fixed nitrogen is consumed by Crocosphaera. Our study quantitatively supports the benefit of nitrogen fixation despite the high electron/energy costs, even when an energetically efficient alternative is available. It demonstrates a competitive aspect of Crocosphaera, permitting them to be regionally significant nitrogen fixers.

• MeSH
• amoniové sloučeniny farmakologie   MeSH
• biologické modely MeSH
• dusík metabolismus   MeSH
• fixace dusíku účinky léků   MeSH
• fosfor metabolismus   MeSH
• fytoplankton účinky léků   metabolismus   MeSH
• počítačová simulace MeSH
• sinice účinky léků   metabolismus   MeSH
• uhlík metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

We introduce a novel framework for conceptualising, quantifying and unifying discordant patterns of species richness along geographical gradients. While not itself explicitly mechanistic, this approach offers a path towards understanding mechanisms. In this study, we focused on the diverse patterns of species richness on mountainsides. We conjectured that elevational range midpoints of species may be drawn towards a single midpoint attractor - a unimodal gradient of environmental favourability. The midpoint attractor interacts with geometric constraints imposed by sea level and the mountaintop to produce taxon-specific patterns of species richness. We developed a Bayesian simulation model to estimate the location and strength of the midpoint attractor from species occurrence data sampled along mountainsides. We also constructed midpoint predictor models to test whether environmental variables could directly account for the observed patterns of species range midpoints. We challenged these models with 16 elevational data sets, comprising 4500 species of insects, vertebrates and plants. The midpoint predictor models generally failed to predict the pattern of species midpoints. In contrast, the midpoint attractor model closely reproduced empirical spatial patterns of species richness and range midpoints. Gradients of environmental favourability, subject to geometric constraints, may parsimoniously account for elevational and other patterns of species richness.

• MeSH
• Bayesova věta MeSH
• biodiverzita * MeSH
• biologické modely * MeSH
• ekosystém * MeSH
• fyziologie rostlin MeSH
• hmyz fyziologie   MeSH
• obratlovci fyziologie   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH

Growing evidence shows that epigenetic mechanisms contribute to complex traits, with implications across many fields of biology. In plant ecology, recent studies have attempted to merge ecological experiments with epigenetic analyses to elucidate the contribution of epigenetics to plant phenotypes, stress responses, adaptation to habitat, and range distributions. While there has been some progress in revealing the role of epigenetics in ecological processes, studies with non-model species have so far been limited to describing broad patterns based on anonymous markers of DNA methylation. In contrast, studies with model species have benefited from powerful genomic resources, which contribute to a more mechanistic understanding but have limited ecological realism. Understanding the significance of epigenetics for plant ecology requires increased transfer of knowledge and methods from model species research to genomes of evolutionarily divergent species, and examination of responses to complex natural environments at a more mechanistic level. This requires transforming genomics tools specifically for studying non-model species, which is challenging given the large and often polyploid genomes of plants. Collaboration among molecular geneticists, ecologists and bioinformaticians promises to enhance our understanding of the mutual links between genome function and ecological processes.

• MeSH
• ekologie * MeSH
• ekosystém MeSH
• epigeneze genetická * MeSH
• metylace DNA MeSH
• rostliny * MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Many mutualisms involve inter-specific resource exchanges, making consumer-resource approaches ideal for studying their dynamics. Also in many cases these resources are short lived (e.g. flowers) compared with the population dynamics of their producers and consumers (e.g. plants and insects), which justifies a separation of time scales. As a result, we can derive the numerical response of one species with respect to the abundance of another. For resource consumers, the numerical responses can account for intra-specific competition for mutualistic resources (e.g. nectar), thus connecting competition theory and mutualism mechanistically. For species that depend on services (e.g. pollination, seed dispersal), the numerical responses display saturation of benefits, with service handling times related with rates of resource production (e.g. flower turnover time). In both scenarios, competition and saturation have the same underlying cause, which is that resource production occurs at a finite velocity per individual, but their consumption tracks the much faster rates of population growth characterizing mutualisms. The resulting models display all the basic features seen in many models of facultative and obligate mutualisms, and they can be generalized from species pairs to larger communities.

• MeSH
• biologické modely * MeSH
• ekosystém MeSH
• opylení MeSH
• populační dynamika MeSH
• šíření semen MeSH
• symbióza * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Omics-based methods are increasingly used in current ecotoxicology. Therefore, a large number of observations for various toxic substances and organisms are available and may be used for identifying modes of action, adverse outcome pathways, or novel biomarkers. For these purposes, good statistical analysis of toxicogenomic data is vital. In contrast to established ecotoxicological techniques, concentration-response modeling is rarely used for large datasets. Instead, statistical hypothesis testing is prevalent, which provides only a limited scope for inference. The present study therefore applied automated concentration-response modeling for 3 different ecotoxicotranscriptomic and ecotoxicometabolomic datasets. The modeling process was performed by simultaneously applying 9 different regression models, representing distinct mechanistic, toxicological, and statistical ideas that result in different curve shapes. The best-fitting models were selected by using Akaike's information criterion. The linear and exponential models represented the best data description for more than 50% of responses. Models generating U-shaped curves were frequently selected for transcriptomic signals (30%), and sigmoid models were identified as best fit for many metabolomic signals (21%). Thus, selecting the models from an array of different types seems appropriate, because concentration-response functions may vary because of the observed response type, and they also depend on the compound, the organism, and the investigated concentration and exposure duration range. The application of concentration-response models can help to further tap the potential of omics data and is a necessary step for quantitative mixture effect assessment at the molecular response level.

• MeSH
• dánio pruhované růst a vývoj   metabolismus   MeSH
• ekosystém * MeSH
• embryo nesavčí účinky léků   metabolismus   MeSH
• genomika * MeSH
• látky znečišťující životní prostředí toxicita   MeSH
• lineární modely MeSH
• metabolomika * MeSH
• rychlé screeningové testy MeSH
• sekvenční analýza hybridizací s uspořádaným souborem oligonukleotidů MeSH
• tetrachlorethylen toxicita   MeSH
• transkriptom účinky léků   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Anthropogenic activities increase pesticide contamination and biological invasions in freshwater ecosystems. Understanding their combined effects on community structure and on ecosystem functioning presents challenges for an improved ecological risk assessment. This study focuses on an artificial stream mesocosms experiment testing for direct and indirect effects of insecticide (chlorantraniliprole - CAP) exposure on the structure of a benthic macroinvertebrate freshwater community and on ecosystem functioning (leaf decomposition, primary production). To understand how predator identity and resource quality alter the community responses to chemical stress, the mediating effects of an invasive predator species (crayfish Procambarus clarkii) and detritus quality (tested by using leaves of the invasive Eucalyptus globulus) on insecticide toxicity were also investigated. Low concentrations of CAP reduced the abundance of shredders and grazers, decreasing leaf decomposition and increasing primary production. Replacement of autochthonous predators and leaf litter by invasive species decreased macroinvertebrate survival, reduced leaf decomposition, and enhanced primary production. Structural equation modeling (SEM) highlighted that CAP toxicity to macroinvertebrates was mediated by the presence of crayfish or eucalypt leaf litter which are now common in many Mediterranean freshwaters. In summary, our results demonstrate that the presence of these two invasive species alters the effects of insecticide exposure on benthic freshwater communities. The approach used here also allowed for a mechanistic evaluation of indirect effects of these stressors and of their interaction on ecosystem functional endpoint, emphasizing the value of incorporating biotic stressors in ecotoxicological experiments.

• MeSH
• ekosystém * MeSH
• insekticidy * MeSH
• listy rostlin MeSH
• řeky MeSH
• sladká voda MeSH
• zavlečené druhy MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Crocosphaera is a major dinitrogen (N2)-fixing microorganism, providing bioavailable nitrogen (N) to marine ecosystems. The N2-fixing enzyme nitrogenase is deactivated by oxygen (O2), which is abundant in marine environments. Using a cellular scale model of Crocosphaera sp. and laboratory data, we quantify the role of three O2 management strategies by Crocosphaera sp.: size adjustment, reduced O2 diffusivity, and respiratory protection. Our model predicts that Crocosphaera cells increase their size under high O2 Using transmission electron microscopy, we show that starch granules and thylakoid membranes are located near the cytoplasmic membranes, forming a barrier for O2 The model indicates a critical role for respiration in protecting the rate of N2 fixation. Moreover, the rise in respiration rates and the decline in ambient O2 with temperature strengthen this mechanism in warmer water, providing a physiological rationale for the observed niche of Crocosphaera at temperatures exceeding 20°C. Our new measurements of the sensitivity to light intensity show that the rate of N2 fixation reaches saturation at a lower light intensity (∼100 μmol m-2 s-1) than photosynthesis and that both are similarly inhibited by light intensities of >500 μmol m-2 s-1 This suggests an explanation for the maximum population of Crocosphaera occurring slightly below the ocean surface.IMPORTANCECrocosphaera is one of the major N2-fixing microorganisms in the open ocean. On a global scale, the process of N2 fixation is important in balancing the N budget, but the factors governing the rate of N2 fixation remain poorly resolved. Here, we combine a mechanistic model and both previous and present laboratory studies of Crocosphaera to quantify how chemical factors such as C, N, Fe, and O2 and physical factors such as temperature and light affect N2 fixation. Our study shows that Crocosphaera combines multiple mechanisms to reduce intracellular O2 to protect the O2-sensitive N2-fixing enzyme. Our model, however, indicates that these protections are insufficient at low temperature due to reduced respiration and the rate of N2 fixation becomes severely limited. This provides a physiological explanation for why the geographic distribution of Crocosphaera is confined to the warm low-latitude ocean.

• MeSH
• fixace dusíku * MeSH
• kyslík metabolismus   MeSH
• sinice cytologie   metabolismus   účinky záření   MeSH
• škrob metabolismus   MeSH
• světlo * MeSH
• teplota * MeSH
• transmisní elektronová mikroskopie MeSH
• tylakoidy metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH

Cíl Neuroendokrinní nádory pankreatu (pancreatic neuroendocrine tumor, PNET), ač vzácné, často metastazují a chirurgická resekce, jediná potenciálně kurativní léčba, tak u nich není možná. Pro nemocné s pokročilými PNET není doposud k dispozici účinná systémová terapie. Z tohoto důvodu jsou potřebné nové léčebné strategie. S tímto cílem realizovali autoři výzkum s využitím preklinických myších modelů PNET, zaměřený na posouzení potenciálního prospěchu terapeutické duální inhibice kinázy receptoru pro epidermální růstový faktor (epidermal growth factor receptor, EGFR) a mTOR (mammalian target of rapamycin – savčí rapamycinový cílený receptor). Materiál a metody Transgenním myším RIP-Tag2 s pokročilými multifokálními PNET byl aplikován inhibitor mTOR rapamycin a inhibitor EGRF erlotinib. Monitorován byl nádorový růst a přežití a dále bylo prováděno vyšetření tumorózních tkání s cílem nalézt potenciální biomarkery odpovědi na podávanou terapii. Výsledky Monoterapie rapamycinem byla výrazně účinná, došlo k prodloužení přežití současně se stabilizací nádorového růstu (stabilní onemocnění). Nakonec však došlo k rozvoji rezistence nádorového onemocnění, což dokazovala progrese růstu tumoru. Monoterapie erlotinibem navodila zpomalení růstu a přinesla hraniční zlepšení přežití. Při použití kombinace obou látek bylo u tohoto agresivního multifokálního nádoru v porovnání s každou z monoterapií zaznamenáno nebývalé zlepšení přežití, přičemž nebyl patrný rozvoj adaptační rezistence. Kromě toho bylo zjištěno, že antiapoptotický protein survivin může sloužit jako biomarker senzitivity a příznivé odpovědi na cílenou duální inhibiční terapii. Závěr Preklinické studie na myších modelech endogenních PNET naznačují, že kombinovaná cílená blokáda signálních drah mTOR a EGFR by mohla přinášet v terapii PNET potenciální klinický prospěch. Uvedené výsledky povzbudily přípravu a realizaci klinické studie fáze II zaměřené na zhodnocení účinnosti tohoto terapeutického režimu u lidských neuroendokrinních nádorů.

• MeSH
• analýza přežití MeSH
• chinazoliny aplikace a dávkování   farmakologie   MeSH
• erbB receptory antagonisté a inhibitory   metabolismus   MeSH
• financování organizované MeSH
• imunohistochemie MeSH
• imunosupresiva aplikace a dávkování   farmakologie   MeSH
• inhibitory apoptózy genetika   metabolismus   MeSH
• inhibitory proteinkinas aplikace a dávkování   farmakologie   MeSH
• intracelulární signální peptidy a proteiny antagonisté a inhibitory   metabolismus   MeSH
• klinické zkoušky, fáze II jako téma MeSH
• lidé MeSH
• modely nemocí na zvířatech MeSH
• myši transgenní MeSH
• myši MeSH
• nádorové buněčné linie MeSH
• neuroendokrinní nádory farmakoterapie   metabolismus   patologie   MeSH
• protein-serin-threoninkinasy antagonisté a inhibitory   metabolismus   MeSH
• proteiny regulující apoptózu metabolismus   MeSH
• protokoly protinádorové kombinované chemoterapie terapeutické užití   MeSH
• represorové proteiny antagonisté a inhibitory   metabolismus   MeSH
• RNA interference MeSH
• signální transdukce účinky léků   MeSH
• sirolimus aplikace a dávkování   farmakologie   MeSH
• TOR serin-threoninkinasy MeSH
• viabilita buněk MeSH
• výsledek terapie MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• myši MeSH
• zvířata MeSH