几种常用的甜味剂对肠道微生物的调节机制

甜味剂是指能赋予软饮料食品甜味的食品添加剂,它可分为高甜度甜味剂和减热值甜味剂。目前甜味剂对肠道菌群的调节机制已成为研究热点之一,甜味剂可影响肠道微生物群的生态平衡,进而影响宿主的健康。越来越多的数据表明,甜味剂的过度食用可致代谢功能障碍,同时对宿主体重和葡萄糖耐受量产生影响。本文综述了近年来几种常用的甜味剂对肠道微生物调节方面的研究进展,以期为研究者提供借鉴。     

The continuing misuse of null hypothesis significance testing in biological anthropology

There is over 60 years of discussion in the statistical literature concerning the misuse and limitations of null hypothesis significance tests (NHST). Based on the prevalence of NHST in biological anthropology research, it appears that the discipline generally is unaware of these concerns. The p values used in NHST usually are interpreted incorrectly. A p value indicates the probability of the data given the null hypothesis. It should not be interpreted as the probability that the null hypothesis is true or as evidence for or against any specific alternative to the null hypothesis. P values are a function of both the sample size and the effect size, and therefore do not indicate whether the effect observed in the study is important, large, or small. P values have poor replicability in repeated experiments. The distribution of p values is continuous and varies from 0 to 1.0. The use of a cut‐off, generally p ≤ 0.05, to separate significant from nonsignificant results, is an arbitrary dichotomization of continuous variation. In 2016, the American Statistical Association issued a statement of principles regarding the misinterpretation of NHST, the first time it has done so regarding a specific statistical procedure in its 180‐year history. Effect sizes and confidence intervals, which can be calculated for any data used to calculate p values, provide more and better information about tested hypotheses than p values and NHST.     

Range‐constrained co‐occurrence simulation reveals little niche partitioning among rock‐dwelling Montenegrina land snails (Gastropoda: Clausiliidae)

Aim

Taxon co‐occurrence analysis is commonly used in ecology, but it has not been applied to range‐wide distribution data of partly allopatric taxa because existing methods cannot differentiate between distribution‐related effects and taxon interactions. Our first aim was to develop a taxon co‐occurrence analysis method that is also capable of taking into account the effect of species ranges and can handle faunistic records from museum databases or biodiversity inventories. Our second aim was to test the independence of taxon co‐occurrences of rock‐dwelling gastropods at different taxonomic levels, with a special focus on the Clausiliidae subfamily Alopiinae, and in particular the genus Montenegrina.

Location

Balkan Peninsula in south‐eastern Europe (46N–36N, 13.5E–28E).

Methods

We introduced a taxon‐specific metric that characterizes the occurrence probability at a given location. This probability was calculated as a distance‐weighted mean of the taxon's presence and absence records at all sites. We applied corrections to account for the biases introduced by varying sampling intensity in our dataset. Then we used probabilistic null‐models to simulate taxon distributions under the null hypothesis of no taxon interactions and calculated pairwise and cumulated co‐occurrences. Independence of taxon occurrences was tested by comparing observed co‐occurrences to simulated values.

Results

We observed significantly fewer co‐occurrences among species and intra‐generic lineages of Montenegrina than expected under the assumption of no taxon interaction.

Main conclusions

Fewer than expected co‐occurrences among species and intra‐generic clades indicate that species divergence preceded niche partitioning. This suggests a primary role of non‐adaptive processes in the speciation of rock‐dwelling gastropods. The method can account for the effects of distributional constraints in range‐wide datasets, making it suitable for testing ecological, biogeographical, or evolutionary hypotheses where interactions of partly allopatric taxa are in question.     

价值工程在医院管理中的应用初探

简述了医院开展价值工程的意义,对价值工程这一工程技术理论如何在医院管理中应用进行了探索,总结了医院的做法和实施效果,为提高医院管理水平,提升核心竞争力提供了一种新的角度。     

森林生态系统服务价值非货币量核算:以京津冀城市群为例

森林生态系统具有重要的功能和服务价值,对其价值的准确核算是实现森林生态系统服务定价、保护森林生态系统和落实“绿水青山就是金山银山”等实际工作的关键前提之一.本研究首先综述了现有森林生态系统服务价值核算方法的优点和局限性,然后构建了基于能值的非货币量的森林生态系统服务价值核算方法,并选取京津冀森林生态系统进行案例研究来测试这一核算方法,又进一步基于归一化植被指数对生态系统服务价值核算结果进行修正,同时考虑到数据获取的不确定性,对核算结果进行了不确定性分析.结果表明: 京津冀不同地区森林生态系统服务价值依次为承德>北京>保定>张家口>石家庄>秦皇岛>天津>邯郸>唐山>邢台>廊坊>衡水>沧州;不同森林生态系统服务价值依次为落叶阔叶林>常绿针叶林>落叶针叶林;就不同生态系统服务子类而言,京津冀单位面积森林生态系统服务价值最大的类型为调节气候,约占单位面积总价值的60%,其次是增加净初级生产力(NPP)和固碳释氧,约占23%,其他子类占比较小;河北省森林生态系统服务价值对当地GDP贡献最大,北京次之,天津最小.本研究构建的森林生态系统服务价值非货币量核算方法,可克服现存研究中存在重复计算、未能真正从生态系统贡献者视角出发、能值转化率使用或替代不当的局限性,系统核算了森林生态系统服务价值,能为实现生态系统服务定价、建立生态补偿机制和加快生态文明体制改革等提供更有效的优化和决策依据.     

Mechanistic studies of sesquiterpene cyclases based on their carbon isotope ratios at natural abundance

During the process of terpene biosynthesis, C–C bond breaking and forming steps are subjected to kinetic carbon isotope effects, leading to distinct carbon isotopic signatures of the products. Accordingly, carbon isotopic signatures could be used to reveal the ‘biosynthetic history’ of the produced terpenoids. Five known sesquiterpene cyclases, regulating three different pathways, representing simple to complex biosynthetic sequences, were heterologously expressed and used for in vitro assays with farnesyl diphosphate as substrate. Compound specific isotope ratio mass spectrometry measurements of the enzyme substrate farnesyl diphosphate (FDP) and the products of all the five cyclases were performed. The calculated δ¹³C value for FDP, based on δ¹³C values and relative amounts of the products, was identical with its measured δ¹³C value, confirming the reliability of the approach and the precision of measurements. The different carbon isotope ratios of the products reflect the complexity of their structure and are correlated with the frequency of carbon–carbon bond forming and breaking steps on their individual biosynthetic pathways. Thus, the analysis of carbon isotopic signatures of terpenes at natural abundance can be used as a powerful tool in elucidation of associated biosynthetic mechanisms of terpene synthases and in future in vivo studies even without ‘touching’ the plant.