The latitudinal gradient in dispersal constraints: ecological specialisation drives diversification in tropical birds

Physiological and behavioural constraints arising from ecological specialisation are proposed to limit gene flow and promote diversification in tropical lineages. In this study, we use phylogenetic analyses to test this idea in 739 Amazonian bird species. We show that patterns of species and subspecies richness are best predicted by a suite of avian specialisms common in tropical avifaunas but rare in the temperate zone. However, this only applied to niche traits associated with dispersal limitation rather than vagility. These findings are consistent with the view that diversity is promoted by more finely partitioned niches, although not simply by coevolutionary adaptation and niche packing as is often assumed. Instead, they suggest that diversification is driven by dispersal constraints, and that niches characterised by these constraints are biased towards tropical systems. We conclude that specialised tropical niches reduce the likelihood of dispersal across barriers, thereby increasing allopatric diversification and contributing to the latitudinal diversity gradient.     

Jack of all nectars, master of most: DNA methylation and the epigenetic basis of niche width in a flower-living yeast

In addition to genetic differences between individuals as a result of nucleotide sequence variation, epigenetic changes that occur as a result of DNA methylation may also contribute to population niche width by enhancing phenotypic plasticity, although this intriguing possibility remains essentially untested. Using the nectar‐living yeast Metschnikowia reukaufii as study subject, we examine the hypothesis that changes in genome‐wide DNA methylation patterns underlie the ability of this fugitive species to exploit a broad resource range in its heterogeneous and patchy environment. Data on floral nectar characteristics and their use by M. reukaufii in the wild were combined with laboratory experiments and methylation‐sensitive amplified polymorphism (MSAP) analyses designed to detect epigenetic responses of single genotypes to variations in sugar environment that mimicked those occurring naturally in nectar. M. reukaufii exploited a broad range of resources, occurring in nectar of 48% of species and 52% of families surveyed, and its host plants exhibited broad intra‐ and interspecific variation in sugar‐related nectar features. Under experimental conditions, sugar composition, sugar concentration and their interaction significantly influenced the mean probability of MSAP markers experiencing a transition from unmethylated to methylated state. Alterations in methylation status were not random but predictably associated with certain markers. The methylation inhibitor 5‐azacytidine (5‐AzaC) had strong inhibitory effects on M. reukaufii proliferation in sugar‐containing media, and a direct relationship existed across sugar × concentration experimental levels linking inhibitory effect of 5‐AzaC and mean per‐marker probability of genome‐wide methylation. Environmentally induced DNA methylation polymorphisms allowed genotypes to grow successfully in extreme sugar environments, and the broad population niche width of M. reukaufii was largely made possible by epigenetic changes enabling genotype plasticity in resource use.     

河西绿洲边缘积沙带与环境因子的关系

绿洲边缘积沙带的形成是一个新的科学问题。甘肃河西地区经过半个多世纪的防沙治沙,在绿洲边缘形成了一条积沙带。为了研究积沙带的形成及其与环境因子的关系,本文对河西走廊东端至走廊中西部绿洲边缘的积沙带进行了调查。结果表明:1)河西走廊东端至中西部绿洲边缘积沙带平均高12.77m,平均带宽308.48m。2)积沙带的宽度与高度呈显著正相关;积沙带的高度与当地的年降水量和年平均风速呈显著正相关;积沙带的增高速率与当地年降水量和年平均风速呈正相关。3)降水条件是决定积沙带高度的关键因子,其次是年平均风速。4)在高大沙丘顶部设置柴草沙障,能促使积沙带(沙丘)继续增高。     

Starch grain morphology of the seagrasses Halodule wrightii, Ruppia maritima, Syringodium filiforme, and Thalassia testudinum

Starch grains are a ubiquitous component of plants that have been used in tandem with phytoliths, pollen, and macrofossils to reconstruct past floral diversity. This tool has yet to be fully explored for aquatic plants, specifically seagrasses, which lack phytoliths and are rarely preserved as macrofossils or pollen. If starch grains in seagrasses are morphologically distinct, this method has the potential to improve seagrass identification in the fossil record in such cases where its starch is preserved (e.g. scratches and occlusal surfaces of tooth enamel from seagrass consumers). The goals of this study were twofold: (1) to determine if starch is present in seagrass material and (2) to assess how starch grain morphology differs between different seagrasses.This study focused on four abundant and ecologically distinct seagrasses from the Caribbean: Halodule wrightii, Ruppia maritima, Syringodium filiforme, and Thalassia testudinum. Starch grains were observed in all species except S. filiforme. Grains from H. wrightii are typically observed in side-on orientation, are sub-round to angular, and are fairly small (3-19 μm, end-on). Grains of R. maritima are small spherical grains (4-8 μm) that have a centric hilum and a straight extinction cross with a median angle between the arms of 90°. Grains from T. testudinum are large (9-31 μm, end-on), conical in side-on and round/sub-round in end-on orientation, have a slightly eccentric hilum with an obvious particle, and prominent lamellae.Visual assessment and comparative statistics demonstrate that the morphology of starch grains from T. testudinum, R. maritima, and H. wrightii are significantly different. With more extensive research, there is potential for the positive identification of starch grains from an unknown seagrass. The ability to identify seagrass from starch grains could facilitate the identification of seagrasses in the fossil record and supply information on seagrass evolution and distribution, climate effects on seagrass distribution, and the diets of seagrass consumers.     

Management of sorghum grain mold through induced resistance mechanism using foliar spray of Pseudomonas fluorescens strains and non-conventional chemicals: a field study

Abstract

The study involved in-vitro and field studies using Pseudomonas fluorescens strains and some non-conventional chemicals for sorghum grain mold management. The culture filtrate of P. fluorescens strains PF-1 and PF-2 inhibited spore germination (p?<?0.001) and mycelial growth of grain mold fungi. Also, tested chemicals and commercial fungicides showed significant mycelial growth inhibition (p?<?0.001). PF-1, PF-2, ZnSO₄·7H₂O, salicylic acid and propiconazole were potentially effective and hence were tested in field (by foliar spraying). Two set of experiments were conducted simultaneously using naturally and artificially (Fusarium challenged) induced infected sorghum panicles. The lowest infection (score 4.2) was recorded with propiconazole. Disease severity was well controlled by PF-1 and PF-2, compared to ZnSO₄·7H₂O and salicylic acid. Furthermore, disease control was validated by determining total phenolic, flavonoid content and differentially induced phenolic acids (HPLC analysis) in harvested grains. Additionally, results of biochemical-traits, compatibility studies and antibiotic sensitivity of strains were found to be favourable.     

多效性基因Ghd7调控水稻剑叶面积

光合作用是植物的唯一能量来源,剑叶是水稻开花后进行光合作用的主要部位。Ghd7是一个多效性产量基因,能显著提高水稻产量。为了研究Ghd7对水稻剑叶形态的遗传效应,文章利用一个包含190个家系的BC2F2群体对水稻剑叶长度(FLL)、剑叶宽(FLW)和剑叶面积(FLA)进行QTL定位分析。在BC2F2群体,FLL、FLW和FLA性状表型值均显示为双峰分布,符合孟德尔单基因分离比,并均与每穗实粒数呈现显著正相关。在第7染色体上RM3859和C39分子标记间定位到FLL、FLW和FLA的QTL,分别解释变异的73.3%、62.3%和71.8%,均与Ghd7共分离。以珍汕97为轮回亲本,特青和明恢63分别为供体亲本,获得两个Ghd7近等基因系NIL(MH63)和NIL(TQ),FLL、FLW和FLA表型值均比珍汕97显著提高。另外,超表达Ghd7的合江19转基因植株的FLL、FLW和FLA表型值分别比合江19增加了8.9 cm、0.5 cm和17.8 cm2。这些结果表明Ghd7对调控剑叶面积起重要作用。     

Novel self-associative and multiphasic nanostructured soft carriers based on amphiphilic hyaluronic acid derivatives

The purpose of the present study was to investigate the physicochemical properties in aqueous media of amphiphilic hyaluronic acid (HA) derivatives obtained by reaction of HA's hydroxyl groups with octenyl succinic anhydride (OSA). The self-associative properties of the resulting octenyl succinic anhydride-modified hyaluronic acid (OSA-HA) derivatives were studied by fluorescence spectroscopy using Nile Red as fluorophore. The morphology, size and surface charge of the OSA-HA assemblies were determined by transmission electron microscopy, dynamic light scattering and by measuring their electrophoretic mobility, respectively. OSA-HA was shown to spontaneously self-associate in aqueous media into negatively charged spherical and multiphasic nanostructures with a hydrodynamic diameter between 170 and 230 nm and to solubilize hydrophobic compounds such as Nile Red. This was a good indication that OSA-HA could be used as building block for the formulation of soft nanocarriers towards the encapsulation and controlled delivery of hydrophobic active ingredients or drugs.     

Yield vs. Quality trade‐offs for wheat in response to carbon dioxide and ozone

Although it is established that there exist potential trade‐offs between grain yield and grain quality in wheat exposed to elevated carbon dioxide (CO₂) and ozone (O₃), their underlying causes remain poorly explored. To investigate the processes affecting grain quality under altered CO₂ and O₃, we analysed 57 experiments with CO₂ or O₃ exposure in different exposure systems. The study covered 24 cultivars studied in 112 experimental treatments from 11 countries. A significant growth dilution effect on grain protein was found: a change in grain yield of 10% by O₃ was associated with a change in grain protein yield of 8.1% (R² = 0.96), whereas a change in yield effect of 10% by CO₂ was linked to a change in grain protein yield effect of 7.5% (R² = 0.74). Superimposed on this effect, elevated CO₂, but not O₃, had a significant negative effect on grain protein yield also in the absence of effects on grain yield, indicating that there exists a process by which CO₂ restricts grain protein accumulation, which is absent for O₃. Grain mass, another quality trait, was more strongly affected by O₃ than grain number, whereas the opposite was true for CO₂. Harvest index was strongly and negatively influenced by O₃, but was unaffected by CO₂. We conclude that yield vs. protein trade‐offs for wheat in response to CO₂ and O₃ are constrained by close relationships between effects on grain biomass and less than proportional effects on grain protein. An important and novel finding was that elevated CO₂ has a direct negative effect on grain protein accumulation independent of the yield effect, supporting recent evidence of CO₂‐induced impairment of nitrate uptake/assimilation. Finally, our results demonstrated that processes underlying responses of grain yield vs. quality trade‐offs are very different in wheat exposed to elevated O₃ compared with elevated CO₂.     

Nitrogen dynamics in grain crop and legume pasture systems under elevated atmospheric carbon dioxide concentration: A meta‐analysis

Understanding nitrogen (N) removal and replenishment is crucial to crop sustainability under rising atmospheric carbon dioxide concentration ([CO₂]). While a significant portion of N is removed in grains, the soil N taken from agroecosystems can be replenished by fertilizer application and N₂ fixation by legumes. The effects of elevated [CO₂] on N dynamics in grain crop and legume pasture systems were evaluated using meta‐analytic techniques (366 observations from 127 studies). The information analysed for non‐legume crops included grain N removal, residue C : N ratio, fertilizer N recovery and nitrous oxide (N₂O) emission. In addition to these parameters, nodule number and mass, nitrogenase activity, the percentage and amount of N fixed from the atmosphere were also assessed in legumes. Elevated [CO₂] increased grain N removal of C₃ non‐legumes (11%), legumes (36%) and C₄ crops (14%). The C : N ratio of residues from C₃ non‐legumes and legumes increased under elevated [CO₂] by 16% and 8%, respectively, but the increase for C₄ crops (9%) was not statistically significant. Under elevated [CO₂], there was a 38% increase in the amount of N fixed from the atmosphere by legumes, which was accompanied by greater whole plant nodule number (33%), nodule mass (39%), nitrogenase activity (37%) and %N derived from the atmosphere (10%; non‐significant). Elevated [CO₂] increased the plant uptake of fertilizer N by 17%, and N₂O emission by 27%. These results suggest that N demand and removal in grain cropping systems will increase under future CO₂‐enriched environments, and that current N management practices (fertilizer application and legume incorporation) will need to be revised.     

Effects of a short-term p-hydroxybenzoic acid application on grain yield and yield components in different tiller categories of spring barley

The aim of these experiments was to evaluate how thresholds for phytotoxic substances obtained in seedling bioassays relate to yield losses or changes in yield components of mature barley crops after a short-term exposure to p-hydroxybenzoic acid. Under laboratory conditions a treatment with 1.81 mM p-hydroxybenzoic acid significantly reduced the radicle length of barley, whereas coleoptile elongation was less sensitive. The inhibition of the radicle length and coleoptile elongation was greater if the pH of the test solution was not buffered at pH 5.5. In a glasshouse trial the effect of p-hydroxybenzoic acid on the radicle and coleoptile elongation of spring barley was compared with the yield response after a three day exposure either during germination or at the double ridge stage of apex development. Applications of 0.72 mM, 1.44 mM and 3.62 mM p-hydroxybenzoic acid averaged over the treatments during germination or at the double ridge stage of development caused a yield reduction in the single ear weight of 5%, 13% and 19% in comparison with the control, respectively. The higher tiller categories in general showed a greater sensitivity towards an application of p-hydroxybenzoic acid and, therefore, could not compensate for the yield decrease of the main stem tiller. A single application of p-hydroxybenzoic acid either at germination or at the double ridge stage may cause yield losses, as reported from no-till systems or cereal monocultures. The data have implications for the interpretation of seedlings bioassays in allelopathic research and their applicability in estimating yield losses caused by phytotoxic substances. ei]Section editor: R Merckx