Shrub cover in northern Nunavik: can herbivores limit shrub expansion?

Recent climate changes have increased the primary productivity of many Arctic and subarctic regions. Erected shrub has been shown to increase in abundance over the last decades in northern regions in response to warmer climate. At the same time, caribou herds are declining throughout the circumboreal regions. Based on observation of heavy browsing on shrubs at Deception Bay (Nunavik, Canada), we hypothesized that the densification of shrubs observed in nearby locations did not occur at our study site despite of observed warming because of a recent peak of the Rivière-aux-Feuilles caribou herd. To assess shrub cover changes, we compared a 1972 mosaic of aerial photos to a 2010 satellite image over a 5 km² area, divided into 56 grids of 100 30 m × 30 m cells. Most cells (n = 4,502) did not show any changes in the cover of shrubs but those who did were as likely to increase as to decrease. The relative cover of shrubs in cells who changed was not higher in 2010 (6.1 ± 0.2 %) than in 1972 (7.3 ± 0.4 %). More than 70 % of birch and willow had more than 50 % of their shoot browsed, suggesting that caribou may limit shrub expansion at this site. We cannot rule out that abiotic factors also contribute to the inertia in shrub cover. Increases in shrub abundance reported in Nunavik and elsewhere were located closer to the tree line or in discontinuous permafrost, whereas our site is characterized by herbaceous arctic tundra, continuous permafrost and relatively low annual precipitation.     

Male-Driven Differences in Chimpanzee (<Emphasis Type=Italic>Pan troglodytes</Emphasis>) Population Genetic Structure Across Three Habitats in Cameroon and Nigeria

Complex ecological pressures affect the social dynamics of many primate species, but it is unclear how they affect primate speciation. Molecular tools are often used to answer questions about the evolutionary histories and social systems of primates. Mitochondrial DNA (mtDNA), in particular, is frequently used to answer many of these questions, but because it is passed from mothers to offspring it reveals only the histories of females. In many species, including chimpanzees, females generally disperse from their natal groups while males are philopatric, and thus differences in dispersal patterns likely leave different signatures in the genome. We previously analyzed samples from 187 unrelated male and female chimpanzees in Nigeria and Cameroon using 21 autosomal microsatellites and mtDNA sequences. Here, we examine the contributions of males and females in shaping the genetic history of these chimpanzees by genotyping a subset of 56 males at 12 Y-chromosome microsatellites. We found that Y-chromosome population structure differed from the results of analysis of mtDNA haplotypes. The results also revealed that males in rainforest habitats (Guinean and Congolian rainforests) are more closely related to one another than those inhabiting the savanna-woodland mosaic ecotone in central Cameroon. In contrast, the pattern of female relatedness did not differ across habitats. We hypothesize that these differences in population structure and patterns of relatedness among males in different habitat types may be due to differences in the community dynamics of chimpanzees in the ecotone vs. rainforests, and that these factors contribute to making Cameroon an engine of diversification for chimpanzees. Broadly, these results demonstrate the importance of habitat variation in shaping social systems, population genetics, and primate speciation.     

猴面包树种子萌发及苗期生长规律研究

在3种处理条件下对猴面包树Adansonia digitata种子进行播种育苗,观察记录种子萌发特性、苗高和地径,以及连续观察两年物候。结果表明：(1)70 ℃热水浸种发芽率和发芽势最高,分别为18.72%、6.20%。(2)苗高和地径增长呈“S”型,苗木生长分为缓慢期、速生期和停滞期;苗高和地径的速生期起点均为7月上旬,一直持续至9月上旬,在8月中旬出现苗高和地径速生点。1年生猴面包树苗高和地径可达81.9 cm和12.6 mm,苗木整齐度较好,苗木质量较高,苗木移栽成活率高达90%以上。(3)在云南元阳县干热河谷地区,2年内猴面包树苗期的物候无显著差异,生长发育正常,证明该地区是猴面包树理想的引种栽培区域之一。     

Particle size influences decay rates of environmental DNA in aquatic systems

Environmental DNA (eDNA) analysis is a powerful tool for remote detection of target organisms. However, obtaining quantitative and longitudinal information from eDNA data is challenging, requiring a deep understanding of eDNA ecology. Notably, if the various size components of eDNA decay at different rates, and we can separate them within a sample, their changing proportions could be used to obtain longitudinal dynamics information on targets. To test this possibility, we conducted an aquatic mesocosm experiment in which we separated fish-derived eDNA components using sequential filtration to evaluate the decay rate and changing proportion of various eDNA particle sizes over time. We then fit four alternative mathematical decay models to the data, building towards a predictive framework to interpret eDNA data from various particle sizes. We found that medium-sized particles (1–10 μm) decayed more slowly than other size classes (i.e., <1 and > 10 μm), and thus made up an increasing proportion of eDNA particles over time. We also observed distinct eDNA particle size distribution (PSD) between our Common carp and Rainbow trout samples, suggesting that target-specific assays are required to determine starting eDNA PSDs. Additionally, we found evidence that different sizes of eDNA particles do not decay independently, with particle size conversion replenishing smaller particles over time. Nonetheless, a parsimonious mathematical model where particle sizes decay independently best explained the data. Given these results, we suggest a framework to discern target distance and abundance with eDNA data by applying sequential filtration, which theoretically has both metabarcoding and single-target applications.     

五种鳗鲡的含肉率及肌肉营养成分分析

研究利用营养测试方法对日本鳗鲡、欧洲鳗鲡、美洲鳗鲡、花鳗鲡和太平洋双色鳗鲡共5种养殖鳗鲡的含肉率及肌肉营养成分进行了分析比较。结果表明: 5种鳗鲡含肉率61.77%69.22%, 日本鳗鲡和太平洋双色鳗鲡显著高于欧洲鳗鲡和花鳗鲡 (P0.05); 水分含量为62.34%71.80%, 粗蛋白含量为11.31% 18.47%, 脂肪含量为8.62% 24.48%, 灰分含量为0.92%1.06%; 均含有18种氨基酸, 其中包括8种人体必须氨基酸, 总氨基酸含量存在差异, 鲜味氨基酸含量占37.43%38.77%, 必需氨基酸指数(EAAI)为65.2574.77, 其构成比例符合FAO/ WHO的标准, 色氨酸、异亮氨基酸和缬氨酸等氨基酸为限制性氨基酸; 富含磷、钾、铁和锌等多种矿物元素, 日本鳗鲡和花鳗鲡含量最高; 均含有16种脂肪酸, 其中饱和脂肪酸(SFA) 7种, 不饱和脂肪酸(UFA)9种; 脂肪酸中多不饱和脂肪酸(PUFA)和二十二碳六烯酸(DHA)含量较高, 分别占总量的41.92%48.27%和6.63%16.87%。研究结果表明: 5种鳗鲡的肌肉为高蛋白、鲜味氨基酸与必需氨基酸含量高的优质蛋白源; 富含磷、钾、铁、锌等矿物元素, 可作为补充人体矿物质营养的膳食来源; 脂肪酸以不饱和脂肪酸为主, 多不饱和脂肪酸和DHA比值高。因此, 5种鳗鲡具有较高的营养价值且有益人体健康, 均是优良的水产养殖种类。       

The Molecular Mechanisms of Protective Role of Se on the G<Subscript>2</Subscript>/M Phase Arrest of Jejunum Caused by AFB<Subscript>1</Subscript>

Aflatoxin B₁ (AFB₁) is the most toxic among the mycotoxins and causes detrimental health effects on human and animals. Selenium (Se) plays an important role in chemopreventive, antioxidant, anticarcinogen, and detoxification and involved in cell cycle regulation. The aim of this study was to explore the molecular mechanisms of selenium involved in inhibition of G₂/M cell cycle arrest of broiler’s jejunum. A total of 240 one-day-old healthy Cobb broilers were randomly divided into four groups and fed with basal diet (control group), 0.6 mg/kg AFB₁ (AFB₁ group), 0.4 mg/kg Se (+Se group), and 0.6 mg/kg AFB₁ + 0.4 mg/kg Se (AFB₁ + Se group) for 21 days, respectively. The histological observation and morphological analysis revealed that 0.4 mg/kg Se prevented the AFB₁-associated lesions of jejunum including the shedding of the apical region of villi, the decreased villus height, and villus height/crypt ratio. The cell cycle analysis by flow cytometry showed that 0.4 mg/kg Se ameliorated the AFB₁-induced G₂/M phase arrest in jejunal cells. Moreover, the expressions of ATM, Chk2, p53, Mdm2, p21, PCNA, Cdc25, cyclin B, and Cdc2 analyzed by immunohistochemistry and qRT-PCR demonstrated that 0.4 mg/kg Se restored these parameters to be close to those in the control group. In conclusion, Se promoted cell cycle recovery from the AFB₁-induced G₂/M phase arrest by the molecular regulation of ATM pathway in the jejunum of broilers. The outcomes from the present study may lead to a better understanding of the nature of selenium’s essentiality and its protective roles against AFB₁.     

The Fission Yeast Minichromosome Maintenance (MCM)-binding Protein (MCM-BP), Mcb1, Regulates MCM Function during Prereplicative Complex Formation in DNA Replication

The minichromosome maintenance (MCM) complex is a replicative helicase, which is essential for chromosome DNA replication. In recent years, the identification of a novel MCM-binding protein (MCM-BP) in most eukaryotes has led to numerous studies investigating its function and its relationship to the MCM complex. However, the mechanisms by which MCM-BP functions and associates with MCM complexes are not well understood; in addition, the functional role of MCM-BP remains controversial and may vary between model organisms. The present study aims to elucidate the nature and biological function of the MCM-BP ortholog, Mcb1, in fission yeast. The Mcb1 protein continuously interacts with MCM proteins during the cell cycle in vivo and can interact with any individual MCM subunit in vitro. To understand the detailed characteristics of mcb1⁺, two temperature-sensitive mcb1 gene mutants (mcb1^ts) were isolated. Extensive genetic analysis showed that the mcb1^ts mutants were suppressed by a mcm5⁺ multicopy plasmid and displayed synthetic defects with many S-phase-related gene mutants. Moreover, cyclin-dependent kinase modulation by Cig2 repression or Rum1 overproduction suppressed the mcb1^ts mutants, suggesting the involvement of Mcb1 in pre-RC formation during DNA replication. These data are consistent with the observation that Mcm7 loading onto replication origins is reduced and S-phase progression is delayed in mcb1^ts mutants. Furthermore, the mcb1^ts mutation led to the redistribution of MCM subunits to the cytoplasm, and this redistribution was dependent on an active nuclear export system. These results strongly suggest that Mcb1 promotes efficient pre-RC formation during DNA replication by regulating the MCM complex.     

响应面法优化重组大肠杆菌产蔗糖异构酶发酵培养基

通过碳氮源的不同浓度对重组大肠杆菌E.coil BL21(DE3)发酵产蔗糖异构酶(SIase)的影响,并借助于数学分析软件Design Expert,结合Plackett-Burman试验设计和中心复合试验设计分析法,对蔗糖异构酶的产生菌进行了发酵培养基的优化研究。实验表明,最佳培养基组分为甘蔗糖蜜10.65 g/L,玉米浆22.22 g/L,NaCl 7.57 g/L ,MgSO₄·7H₂O 0.52 g/L, KH₂PO₄ 4.46g/L,优化后的蔗糖异构酶活力达到29.1U/ml,比LB培养基培养重组大肠杆菌(15U/ml),蔗糖异构酶活力提高了94%,与原始菌大黄欧文菌NX-5相比提高了21.4倍(1.3U/ml)。