川西峨眉晚白垩世夹关期河流沉积中的痕迹化石群落*

晚白垩世夹关组中的痕迹化石群落至少由12个痕迹属17个痕迹种组成,其中包括5个新痕迹种,即Cystichrtium cuwatitivum,Steinichnus laryus,Paradidymaulichnus emeiertsis,Monmorphichnus lineates和Rusophycus univalvis.这一化石群落主要是无脊椎动物的进食迹、觅食迹、爬迹、停息迹和居住迹,其中多数呈下浮痕和全浮痕保存,并形成于经常干旱的河流环境(大多出现在泛滥平原沉积中).该群落可识别出两个痕迹化石组合,即1) Scoyenia-Steinichnus-Rusophycus组合,它主要产自泛滥平原和漫滩环境;2)Skolithos-Arenicolites组合,它代表一种水道砂坝或曲流砂坝环境.     

Culture of rotifers with reference to some physico-chemical properties of water in nursery pond

Rotifers were cultured with five different organic and inorganic fertilizers in nursery ponds. Of the fertilizers used, mustard oil cake gave significantly (p < 0.01) higher production of rotifers than that of mohua oil cake followed by cow-dung, wheat bran, mixture of NPK and control. The higher production of rotifers was directly related with the higher doses of fertilizers. Among the rotifer species identified, the abundance of Brachionus caudatus and B. forficula were significantly (p < 0.01) higher than others. Available N, available P, exchangeable K and exchangeable Ca and exchangeable Mg were generally higher in ponds where organic fertilizers were used. Proximate composition of rotifers varied depending on the kinds of fertilizers. The multiple correlations of physico-chemical properties were highly significant (p < 0.01) with the growth and production of B. caudatus (R = 0.995), B. forficula (R = 0.932), Trichocerca capucina (R = 0.917), B. patulus (R = 0.901) and B. angularis (R = 0.892) and simply significant (p < 0.05) in the case of Keratella tropica (R = 0.880), Hexarthra intermadia (R = 0.875), B. calyciflorus (R = 0.864) and Filinia spp. (R = 0.856) contributing 91.20%, 86.86%, 84.09%, 81.18%, 79.57%, 77.44%, 76.56%, 74.65% and 73.27% of total effect of water properties on the growth of these species, respectively. The residual effect of nine different physico-chemical properties of water on the production of rotifers was 78.92% which indicates that these properties of water had only 21.08% influence on the production of rotifers.     

Endonuclease-sensitive DNA modifications induced by acetone and acetophenone as photosensitizers.

Repair endonucleases, viz. endonuclease III, formamidopyrimidine-DNA glycosylase (FPG protein), endonuclease IV, exonuclease III and UV endonuclease, were used to analyse the modifications induced in bacteriophage PM2 DNA by 333 nm laser irradiation in the presence of acetone or acetophenone. In addition to pyrimidine dimers sensitive to UV endonuclease, 5,6-dihydropyrimidines (sensitive to endonuclease III) and base modifications sensitive to FPG protein were generated. The level of the last in the case of acetone was 50% and in the case of acetophenone 9% of the level of pyrimidine dimers. HPLC analysis of the bases excised by FPG protein revealed that least some of them were 8-hydroxyguanine (7,8-dihydro-8-oxoguanine). In the damage induced by direct excitation of DNA at 254 nm, which was analysed for comparison, the number of FPG protein-sensitive base modifications was only 0.6% of that of the pyrimidine dimers. Mechanistic studies demonstrated that the formation of FPG protein-sensitive modifications did not involve singlet oxygen, as the damage was not increased in D2O as solvent. Hydroxyl radicals, superoxide and H2O2 were also not involved, since the relative number of single strand breaks and of sites of base loss (AP sites) was much lower than in the case of DNA damage induced by hydroxyl radicals and since the presence of SOD or catalase had no effect on the extent of the damage. However, the mechanism did involve an intermediate that was much more efficiently quenched by azide ions than the triplet excited carbonyl compounds and which was possibly a purine radical. Together, the data indicate that excited triplet carbonyl compounds react with DNA not only by triplet-triplet energy transfer yielding pyrimidine dimers, but also by electron transfer yielding preferentially base modifications sensitive to FPG protein, which include 8-hydroxyguanine.     

Evidence for the Predator Attraction Hypothesis in an amphibian predator–prey system

Many species possess damage-released chemical alarm cues that function in alerting nearby individuals to a predator attack. One hypothesis for the evolution and/or maintenance of such cues is the Predator Attraction Hypothesis, where predators, rather than prey, are the “intended” recipients of these cues. If a predator attack attracts additional predators, these secondary predators might interfere with the predation event, providing the prey with a better chance to escape. In this study, we conducted two experiments to explore this hypothesis in an amphibian predator/prey system. In Experiment 1, we found that tiger salamanders (Ambystoma mavortium) showed a foraging attraction to chemical cues from wood frog (Lithobates sylvaticus) tadpoles. Salamanders that were experienced with tadpole prey, in particular, were strongly attracted to tadpole alarm cues. In Experiment 2, we observed experimental encounters between a tadpole and either one or two salamanders. The presence of the second predator caused salamanders to increase attack speed at the cost of decreased attack accuracy (i.e., increasing the probability that the tadpole would escape attacks). We also found that the mere presence of visual and chemical cues from a second predator did not affect this speed/accuracy trade-off but did cause enough of a distraction to increase tadpole survival. Thus, our findings are consistent with the Predator Attraction Hypothesis for the evolution and/or maintenance of alarm cues.     

UreB immunodominant epitope-specific CD8+ T-cell responses were beneficial in reducing gastric symptoms in Helicobacter pylori-infected individuals

Background and aims

Although Helicobacter pylori is recognized as an extracellular infection bacterium, it can lead to an increase in the number of CD8⁺ T cells after infection. At present, the characteristics of H. pylori antigen-specific CD8⁺ T cells and the epitope response have not been elucidated. This study was focused on putative protective antigen UreB to detect specific CD8⁺ T-cell responses in vitro and screen for predominant response epitopes.

Methods

The PBMCs collected from H. pylori-infected individuals were stimulated by UreB peptide pools in vitro to identify the immunodominant CD8⁺ T-cell epitopes. Furthermore, their HLA restriction characteristics were detected accordingly by NGS. Finally, the relationship between immunodominant responses and appearance of gastric symptoms after H. pylori infection was conducted.

Results

UreB-specific CD8⁺ T-cell responses were detected in H. pylori-infected individuals. Three of UreB dominant epitopes (A-2 (UreB_443–451: GVKPNMIIK), B-4 (UreB_420–428: SEYVGSVEV), and C-1 (UreB_5–13: SRKEYVSMY)) were firstly identified and mainly presented by HLA-A*1101, HLA-B*4001 and HLA-C*0702 alleles, respectively. C-1 responses were mostly occurred in H. pylori-infected subjects without gastric symptoms and may alleviate the degree of gastric inflammation.

Conclusions

The UreB dominant epitope-specific CD8⁺ T-cell response was closely related to the gastric symptoms after H. pylori infection, and the C-1 (UreB_5-13) dominant peptides may be protective epitopes.     

Three-dimensional species distribution modelling reveals the realized spatial niche for coral recruitment on contemporary Caribbean reefs

The three-dimensional structure of habitats is a critical component of species' niches driving coexistence in species-rich ecosystems. However, its influence on structuring and partitioning recruitment niches has not been widely addressed. We developed a new method to combine species distribution modelling and structure from motion, and characterized three-dimensional recruitment niches of two ecosystem engineers on Caribbean coral reefs, scleractinian corals and gorgonians. Fine-scale roughness was the most important predictor of suitable habitat for both taxa, and their niches largely overlapped, primarily due to scleractinians' broader niche breadth. Crevices and holes at mm scales on calcareous rock with low coral cover were more suitable for octocorals than for scleractinian recruits, suggesting that the decline in scleractinian corals is facilitating the recruitment of octocorals on contemporary Caribbean reefs. However, the relative abundances of the taxa were independent of the amount of suitable habitat on the reef, emphasizing that niche processes alone do not predict recruitment rates.     

Insertional mutagenesis to isolate acetate-requiring mutants in Chlamydomonas reinhardtii

Abstract An arg 7 mutant of the green alga Chlamydomonas reinhardtii was transformed with pARG7.8, a plasmid bearing the wild-type ARG 7 gene. Out of 4100 arg⁺ transformants selected on an arginine-free medium supplemented with acetate, nine failed to grow on acetate-free medium (ac⁻ mutants). The results of the genetic and molecular analysis of several ac⁻ mutants are in agreement with the hypothesis that they originated from insertion of the incoming plasmid into the nuclear genome. These mutants should constitute valuable tools for isolating the corresponding wild-type genes after plasmid rescue into Escherichia coli .     

Reduction in animal abundance and oxygen availability during and after the end-Triassic mass extinction

The end-Triassic biodiversity crisis was one of the most severe mass extinctions in the history of animal life. However, the extent to which the loss of taxonomic diversity was coupled with a reduction in organismal abundance remains to be quantified. Further, the temporal relationship between organismal abundance and local marine redox conditions is lacking in carbonate sections. To address these questions, we measured skeletal grain abundance in shallow-marine limestones by point counting 293 thin sections from four stratigraphic sections across the Triassic/Jurassic boundary in the Lombardy Basin and Apennine Platform of western Tethys. Skeletal abundance decreased abruptly across the Triassic/Jurassic boundary in all stratigraphic sections. The abundance of skeletal organisms remained low throughout the lower-middle Hettangian strata and began to rebound during the late Hettangian and early Sinemurian. A two-way ANOVA indicates that sample age (p < .01, η² = 0.30) explains more of the variation in skeletal abundance than the depositional environment or paleobathymetry (p < .01, η² = 0.15). Measured I/Ca ratios, a proxy for local shallow-marine redox conditions, show this same pattern with the lowest I/Ca ratios occurring in the early Hettangian. The close correspondence between oceanic water column oxygen levels and skeletal abundance indicates a connection between redox conditions and benthic organismal abundance across the Triassic/Jurassic boundary. These findings indicate that the end-Triassic mass extinction reduced not only the biodiversity but also the carrying capacity for skeletal organisms in early Hettangian ecosystems, adding to evidence that mass extinction of species generally leads to mass rarity among survivors.     

Identification of a UDP-glucosyltransferase conferring deoxynivalenol resistance in Aegilops tauschii and wheat

Aegilops tauschii is the diploid progenitor of the wheat D subgenome and a valuable resource for wheat breeding, yet, genetic analysis of resistance against Fusarium head blight (FHB) and the major Fusarium mycotoxin deoxynivalenol (DON) is lacking. We treated a panel of 147 Ae. tauschii accessions with either Fusarium graminearum spores or DON solution and recorded the associated disease spread or toxin-induced bleaching. A k-mer-based association mapping pipeline dissected the genetic basis of resistance and identified candidate genes. After DON infiltration nine accessions revealed severe bleaching symptoms concomitant with lower conversion rates of DON into the non-toxic DON-3-O-glucoside. We identified the gene AET5Gv20385300 on chromosome 5D encoding a uridine diphosphate (UDP)-glucosyltransferase (UGT) as the causal variant and the mutant allele resulting in a truncated protein was only found in the nine susceptible accessions. This UGT is also polymorphic in hexaploid wheat and when expressed in Saccharomyces cerevisiae only the full-length gene conferred resistance against DON. Analysing the D subgenome helped to elucidate the genetic control of FHB resistance and identified a UGT involved in DON detoxification in Ae. tauschii and hexaploid wheat. This resistance mechanism is highly conserved since the UGT is orthologous to the barley UGT HvUGT13248 indicating descent from a common ancestor of wheat and barley.