黑斑羚粪便中碳同位素揭示的食性变化

利用稳定碳同位素数据(δ13C)分析了南非克鲁格国家公园混食性黑斑羚(Aepyceros melampus)时间和空间尺度上的食性变化,验证了两个假说,即有蹄类食性变化是由生境中木本植物与草本植物的相对配比导致;降雨控制有蹄类生态。结果表明:黑斑羚的食性涵盖了精食者-粗食者采食谱系,且食性中木本与草本比例在不同月间、季节、年度和区域间存在很大变化。栖息于开放性热带稀树草原和草原中的黑斑羚通常采食比生境中更高比例的草本,但在时间尺度上并不恒定。在克鲁格北部的一个区域(Punda Maria) ,黑斑羚采食的草本比克鲁格国家公园中其它任何区域都多。与其它生境相比,在河边的黑斑羚采食草本数量更少,尤其是在食性空间变化更为明显的旱季。因此,我们的数据不支持有蹄类食性组成变化是由生境中木本与草本比例不同造成的假说,食性与降雨量间也无明显的关系。我们的结果支持草本中蛋白含量增加引起黑斑羚采食比例的增加这一模型。粪便中氮含量在时间和空间上的变化很小,揭示在可利用食物中,无论木本还是草本,黑斑羚进行选择采食以保证最好的食物质量。基于这些结果,我们认为更具体的食物选择和可利用性最适采食理论能够更好地解释这种生态学变化。     

The F box protein S phase kinase-associated protein 2 regulates adipose mass and adipocyte number in vivo

Objective: The etiology of some obesity may involve adipocyte hyperplasia. However, the role of adipocyte number in establishing adipose mass is unclear. Cyclin‐dependent kinase inhibitor p27 regulates activity of cyclin/cyclin‐dependent kinase complexes responsible for cell cycle progression. This protein is critical for establishing adult adipocyte number, and p27 knockout increases adult adipocyte number. The SCF (for Skp1‐Cullin‐F‐box protein) complex targets proteins such as p27 for ubiquitin‐proteosome degradation; the F box protein S phase kinase‐associated protein 2 (Skp2), a component of the SCF complex, specifically recognizes p27 for degradation. We used Skp2 knockout (Skp2^?/?) mice to test whether Skp2 loss decreased adipose mass and adipocyte number. Research Methods and Procedures: We measured body weight, adipose mass, adipocyte diameter and number, and glucose tolerance in wild‐type (WT), Skp2^?/?, and p27^?/?Skp2^?/? mice. Mouse embryo fibroblasts (MEFs) from WT and Skp2^?/? fetuses were differentiated to determine whether Skp2 directly affected adipogenesis. Results: Skp2^?/? mice had a 50% decrease in both subcutaneous and visceral fat pad mass and adipocyte number; these decreases exceeded those in body weight, kidney, or muscle. To test the hypothesis that Skp2 effects on adipocyte number involved p27 accumulation, we used p27^?/?Skp2^?/? double knockout mice. The Skp2^?/? decrements in adipocyte number and fat pad mass were totally reversed in p27^?/?Skp2^?/? mice. Adipogenesis was inhibited in MEFs from Skp2^?/? vs. WT mice, and this inhibition was absent in MEFs from p27^?/?Skp2^?/? mice. Discussion: Our results indicate that Skp2 regulates adipogenesis and ultimate adipocyte number in vivo; thus, Skp2 may contribute to obesity involving adipocyte hyperplasia.     

The contribution of abiotic processes to buried litter decomposition in the northern Chihuahuan desert

Summary Creosobebush (Larrea tridentata) fine litter was treated with either the general biocide HgCl₂ and CuSO₄ or water (controls) and buried 5 cm beneath the soil surface in the northern Chihuahuan Desert. The treated litter showed significantly less mass loss than controls during the three month summer-autumn field study; controls lost about 20% of the original mass while treated litter lost less than 2%. In addition, the total nitrogen content of the control litter increased from an initial concentration of about 14.08 g kg^-1 to 17.62 g kg^-1 dry weight by the end of the study, while treated litter nitrogen content decreased to 13.30 g kg^-1. Results suggest abiotic processes other than leaching have little effect on the decomposition of buried litter in this environment.     

NVP-DPP728 (1-[[[2-[(5-cyanopyridin-2-yl)amino]ethyl]amino]acetyl]-2-cyano-(S)- pyrrolidine), a slow-binding inhibitor of dipeptidyl peptidase IV.

Inhibition of dipeptidyl peptidase IV (DPP-IV) has been proposed recently as a therapeutic approach to the treatment of type 2 diabetes. N-Substituted-glycyl-2-cyanopyrrolidide compounds, typified by NVP-DPP728 (1-[[[2-[(5-cyanopyridin-2-yl)amino]ethyl]amino]acetyl]-2-cyano-(S )-p yrrolidine), inhibit degradation of glucagon-like peptide-1 (GLP-1) and thereby potentiate insulin release in response to glucose-containing meals. In the present study NVP-DPP728 was found to inhibit human DPP-IV amidolytic activity with a K(i) of 11 nM, a k(on) value of 1.3 x 10(5) M(-)(1) s(-)(1), and a k(off) of 1.3 x 10(-)(3) s(-)(1). Purified bovine kidney DPP-IV bound 1 mol/mol [(14)C]-NVP-DPP728 with high affinity (12 nM K(d)). The dissociation constant, k(off), was 1.0 x 10(-)(3) and 1.6 x 10(-)(3) s(-)(1) in the presence of 0 and 200 microM H-Gly-Pro-AMC, respectively (dissociation t(1/2) approximately 10 min). Through kinetic evaluation of DPP-IV inhibition by the D-antipode, des-cyano, and amide analogues of NVP-DPP728, it was determined that the nitrile functionality at the 2-pyrrolidine position is required, in the L-configuration, for maximal activity (K(i) of 11 nM vs K(i) values of 5.6 to >300 microM for the other analogues tested). Surprisingly, it was found that the D-antipode, despite being approximately 500-fold less potent than NVP-DPP728, displayed identical dissociation kinetics (k(off) of 1.5 x 10(-)(3) s(-)(1)). NVP-DPP728 inhibited DPP-IV in a manner consistent with a two-step inhibition mechanism. Taken together, these data suggest that NVP-DPP728 inhibits DPP-IV through formation of a novel, reversible, nitrile-dependent complex with transition state characteristics.     

Large-Scale Mapping of Transposable Element Insertion Sites Using Digital Encoding of Sample Identity

Determining the genomic locations of transposable elements is a common experimental goal. When mapping large collections of transposon insertions, individualized amplification and sequencing is both time consuming and costly. We describe an approach in which large numbers of insertion lines can be simultaneously mapped in a single DNA sequencing reaction by using digital error-correcting codes to encode line identity in a unique set of barcoded pools.     

Mapping of Fhb2 on chromosome 6BS: a gene controlling Fusarium head blight field resistance in bread wheat (Triticum aestivum L.)

Fusarium head blight (FHB) is one of the most important fungal wheat diseases worldwide. Understanding the genetics of FHB resistance is key to facilitate the introgression of different FHB resistance genes into adapted wheat. The objective of this project was to study the FHB resistance QTL on chromosome 6B, quantify the phenotypic variation, and qualitatively map the resistance gene as a Mendelian factor. The FHB resistant parent BW278 (AC Domain*2/Sumai 3) was used as the source of the resistance allele. A large recombinant inbred line (RIL) mapping population was developed from the cross BW278/AC Foremost. The population segregated for three known FHB resistance QTL located on chromosomes 3BSc, 5A, and 6B. Molecular markers on chromosome 6B (WMC104, WMC397, GWM219), 5A (GWM154, GWM304, WMC415), and 3BS (WMC78, GWM566, WMC527) were amplified on approximately 1,440 F_2:7 RILs. The marker information was used to select 89 RILs that were fixed homozygous susceptible for the 3BSc and 5A FHB QTLs and were recombinant in the 6B interval. Disease response was evaluated on 89 RILs and parental checks in the greenhouse and field nurseries. Dual floret injection (DFI) was used in greenhouse trials to evaluate disease severity (DS). Macroconidial spray inoculations were used in field nurseries conducted at two locations in southern Manitoba (Carman and Glenlea) over two years 2003 and 2004, to evaluate disease incidence, disease severity, visual rating index, and Fusarium-damaged kernels. The phenotypic distribution for all five-disease infection measurements was bimodal, with lines resembling either the resistant or susceptible checks and parents. All of the four field traits for FHB resistance mapped qualitatively to a coincident position on chromosome 6BS, flanked by GWM133 and GWM644, and is named Fhb2. The greenhouse-DS trait mapped 2 cM distal to Fhb2. Qualitative mapping of Fhb2 in wheat provides tightly linked markers that can reduce linkage drag associated with marker assisted selection of Fhb2 and aid the pyramiding of different resistance loci for wheat improvement.     

Acute toxicity of lead, steel, and an iron-tungsten-nickel shot to mallard ducks (Anas platyrhynchos)

Twenty mallards (Anas platyrhynchos) of both sexes were dosed by oral gavage with Heavi-Shot (H-S; Environ-Metal, Inc., Sweet Home, Oregon, USA) pellets, 20 with steel shot, and 10 with lead (Pb) pellets, all of equal size. All pellets were fired from a shotgun into an absorbent material, retrieved, and weighed prior to introduction into the ducks. Birds were fed whole kernel corn and grit and observed for signs of toxicity for 30 days following dosing. Hevi-Shot pellets lost an average of 6.2% of their mass and steel shot pellets lost 57% of their mass in the birds' gizzards. Almost all (90%) of the Pb shot dosed birds died before the end of the study, while no mortality was observed in the steel or H-S dosed groups. Even though total food consumption differed between the H-S and steel shot groups, mean bird weight change was not different. There were no significant morphologic or histopathologic abnormalities of the liver and kidney in the H-S and steel shot groups. Results indicated that mallards dosed orally with eight No. 4 H-S pellets were not adversely affected over a 30-day period, and that H-S provides another environmentally safe nontoxic shot for use in waterfowl hunting.     

Microbial substrate preference and community dynamics during decomposition of Acer saccharum

The Guild Decomposition Model (GDM) hypothesized that temporal shifts in microbial “guilds,” each with distinct substrate preferences, drive decomposition dynamics and regulate soil carbon (C) losses and sequestration. To test this hypothesis, we established a laboratory incubation of Acer saccharum litter and monitored respiration, microbial biomass and enzyme activities, inorganic nutrients and shifts in functional groups of decomposers using phospholipid fatty acid (PLFA) analysis. Biomass and respiration peaked within the first 2 d of incubation, and the Gram negative PLFA biomarker 18:1ω7c predominated during the first 5 d. Hydrolytic enzyme activities and two fungal biomarkers (18:2ω6,9c and 18:3ω6c) increased by 25 d and lignolytic enzyme activity was detected at 68 d. Our results suggest that decomposers preferentially use labile substrates and that shifts in decomposer groups occur in response to changes in available substrates, which supports the GDM.     

Effects of Frequent Mowing on Survival and Persistence of Forbs Seeded into a Species-Poor Grassland

Many early attempts at tallgrass prairie reconstruction failed to achieve the high species diversity of remnant prairies, and instead consist primarily of C₄ grasses. We hypothesized that frequent mowing of established prairie grasses could create sufficient gaps in the aboveground and belowground environment to allow for the establishment of native forbs from seed. We studied forb seedling establishment in a 25‐year‐old prairie planting in northern Iowa that was dominated by native warm‐season grasses. In winter 1999, 23 species of native forbs were broadcast into the recently burned sod at a rate of 350 viable seeds/m². Treatment plots were mowed weekly for either one or two growing seasons, and control plots were unmowed. Mowed plots had greater light availability than controls, especially when warm‐season grasses began to flower. Overwinter seedling mortality was 3% in mowed treatments compared to 29% in the controls. Forbs in mowed plots had significantly greater root and shoot mass than those in control plots in the first and second growing seasons but were not significantly more abundant. By the fourth growing season, however, forbs were twice as abundant in the mowed treatments. No lasting negative impacts of frequent mowing on the grass population were observed. Mowing a second year influenced species composition but did not change total seedling establishment. Experimental evidence is consistent with the idea that mowing reduced competition for light from large established grasses, allowing forb seedlings the opportunity to reach sufficient size to establish, survive, and flower in the second and subsequent years.     

Evidence that ethanol acts on a target in Loop 2 of the extracellular domain of alpha1 glycine receptors

Considerable evidence indicates that ethanol acts on specific residues in the transmembrane domains of glycine receptors (GlyRs). In this study, we tested the hypothesis that the extracellular domain is also a target for ethanol action by investigating the effect of cysteine substitutions at positions 52 (extracellular domain) and 267 (transmembrane domain) on responses to n-alcohols and propyl methanethiosulfonate (PMTS) in alpha1GlyRs expressed in Xenopus oocytes. In support of the hypothesis: (i) The A52C mutation changed ethanol sensitivity compared to WT GlyRs; (ii) PMTS produced irreversible alcohol-like potentiation in A52C GlyRs; and (iii) PMTS binding reduced the n-chain alcohol cutoff in A52C GlyRs. Further studies used PMTS binding to cysteines at positions 52 or 267 to block ethanol action at one site in order to determine its effect at other site(s). In these situations, ethanol caused negative modulation when acting at position 52 and positive modulation when acting at position 267. Collectively, these findings parallel the evidence that established the TM domain as a target for ethanol, suggest that positions 52 and 267 are part of the same alcohol pocket and indicate that the net effect of ethanol on GlyR function reflects the summation of its positive and negative modulatory effects on different targets.