Changes in niche differentiation and environmental filtering over a hydric stress gradient

群落的多样性取决于物种相互共存的能力,以及克服环境胁迫的能力,从而可能扮演一个环境过滤器的角色。生态位分化导致了比种间竞争更强的种内竞争,促进了物种共存。由于胁迫影响相互作用,生态位分化的强度可能沿胁迫作用的梯度发生变化。在有胁迫的栖息地,如沙漠和高山地区,植物的生长形式更加多样化,这表明在环境胁迫下植物具有更强的生态位分化。我们验证了生态位差异和环境过滤作用随着环境胁迫的增加而增强的假设。在墨西哥南部的半干旱草原上,我们沿着水分胁迫梯度在田间种植了6种一年生植物。植物进行三种种植处理：单独种植(没有相互作用),与同种植物为邻(种内相互作用)或与异种植物为邻(种间相互作用)。我们分析了种内与种间竞争的比值是如何沿水分胁迫梯度变化的,以评估水分如何决定生态位分化的强度。我们还测定了水分胁迫是否代表了一种环境过滤作用。我们发现了种内竞争比种间竞争更强,尤其是在水分胁迫更大的情况下。因此,我们的结果表明,除了一个物种外,所有物种至少在部分水分胁迫梯度下存在生态位分化。一些物种受到胁迫的阻碍,而另一些物种可能因为胁迫消除了土壤病原体而受到它的青睐。虽然高强度的生态位分化在环境胁迫下出现的频率略高,但由于我们的物种样本很小,而且这种通用的模式也存在例外,因此需要进一步的研究来确定这是否是自然界普遍存在的现象。     

Bacteriophage MS2 displays unreported capsid variability assembling T = 4 and mixed capsids

Bacteriophage MS2 is a positive-sense, single-stranded RNA virus encapsulated in an asymmetric T = 3 pseudo-icosahedral capsid. It infects Escherichia coli through the F-pilus, in which it binds through a maturation protein incorporated into its capsid. Cryogenic electron microscopy has previously shown that its genome is highly ordered within virions, and that it regulates the assembly process of the capsid. In this study, we have assembled recombinant MS2 capsids with non-genomic RNA containing the capsid incorporation sequence, and investigated the structures formed, revealing that T = 3, T = 4 and mixed capsids between these two triangulation numbers are generated, and resolving structures of T = 3 and T = 4 capsids to 4 Å and 6 Å respectively. We conclude that the basic MS2 capsid can form a mix of T = 3 and T = 4 structures, supporting a role for the ordered genome in favouring the formation of functional T = 3 virions.     

Evidence of doubly uniparental inheritance of the mitochondrial DNA in Polititapes rhomboides (Bivalvia,Veneridae): Evolutionary and population genetic analysis of F and M mitotypes

Doubly uniparental inheritance (DUI) is a particular mitochondrial DNA inheritance mode reported in a number of bivalves. DUI species show two types of mtDNA, one transmitted from females to daughters and sons (F mitotype) and another one from males to sons (M mitotype). In Veneridae, the existence of DUI has been investigated in several species but it was found in only two of them. In this study, we obtained partial sequences of rrnL, cytb and cox1 genes of males and females of Polititapes rhomboides from NW Spain and we demonstrated the existence of heteroplasmy in males, as expected under DUI. F and M mitotypes showed a taxon-specific phylogenetic pattern and similar evolutionary rates. We focused on cox1 for population genetic analysis, examining separately F and M mitotypes, but also F mitotypes from females (F_♀) and males (F_♂). In all cases, cox1 bears signs of strong purifying selection, with no apparent evidence of relaxed selection in the M genome, while the divergence between F and M genomes is in agreement with the neutral model of evolution. The cox1 polymorphism, higher at the M than at the F genome, also shows clear footprints of genetic hitchhiking with favourable mutations at other mtDNA loci, except for F_♂. In terms of population structure, results suggest that the pattern depends on the examined mitotype (F, F_♀, F_♂ or M).     

Response of transgenic tobacco overexpressing the CchGLP gene to cadmium and aluminium: phenotypic and microRNAs expression changes

Physiology and Molecular Biology of Plants - Transgenic tobacco (N. tabacum cv. Xanthi nc) expressing Capsicum chinense CchGLP gene that encodes an Mn-SOD, constitutively produces hydrogen...     

Antifeedant Activity of <i>Caesalpinia coriaria</i> Essential Oil Against <i>Incisitermes marginipennis</i> (Latreille)

This study scrutinized the possibility of finding toxicant or deterrent plant metabolites against the dry wood termite Incisitermes marginipennis (Latreille). Plant deterrent agents act as repellents or antifeedants to prevent wood decay and increase its useful life. The potential of the tree Caesalpinia coriaria (Fabaceae) as a biological source of molecules with deterrent effects against the dry wood termite was assessed by a phytochemical fractionation guided by repellence and antifeedant activities. The gas chromatography-mass spectrometry analysis of the leaf essential oil showed geraniol to be one of the major components and its repellent and antifeedant effects were determined. Geraniol had only an antifeedant effect without affecting the body weight or survival of the dry wood termite. Unlike the leaf essential oil, geraniol did not exhibit a repellency effect. An in-silico approach of the activity of acetylcholinesterase in interaction with geraniol resulted in an affinity energy of −7.5 Kcal/mol. Geraniol interacted with the amino acid tyrosine 324 located in the enzyme’s active site while citronellol (negative control) interacted with tryptophan 83 located adjacent to the active site. These deterring terpenes have not been implemented for the preservation and restoration of wood products exposed to the attack of the dry wood termite. However, they are an important natural control alternative.     

Interaction of <i>Acaena elongata</i> L. with Arbuscular Mycorrhizal Fungi under Phosphorus Limitation Conditions in a Temperate Forest

The aim of this study was to analyze the performance of Acaena elongata colonized by arbuscular mycorrhizal fungi (AMF) to different phosphorus (P) concentrations, as a measure of AMF dependency. A. elongata, is a species from soils where P availability is limited, such as temperate forests. Our research questions were: 1) How do different P concentrations affect the AMF association in Acaena elongata, and 2) How does the AMF association influence A. elongata’s growth under different P concentrations? A. elongata’s growth, P content in plant tissue, AMF colonization and dependency were measured under four P concentrations: control (0 g P kg⁻¹ ), low (0.05 g P kg⁻¹ ), intermediate (0.2 g P kg⁻¹ ) and high (2 g P kg⁻¹ ) in different harvests. A complete randomized block design was applied. A. elongata’s growth was higher under -AMF in intermediate and high P concentrations, and the lowest growth corresponded to +AMF in the low and intermediate P concentration. We observed a negative effect on the root biomass under +AMF in intermediate P concentration, while the P concentration had a positive effect on the leaf area ratio. The AMF colonization in A. elongata decreased in the highest P concentration and it was favored under intermediate P concentration; while the low and the high concentrations generated a cost-benefit imbalance. Our results suggest that the performance of some plant species in soils with low P availability may not be favored by their association with AMF, but a synergy between AMF and intermediate P concentrations might drive A. elongata’s growth.     

Possible Ancestral Functions of the Genetic and RNA Operational Precodes and the Origin of the Genetic System

Origins of Life and Evolution of Biospheres - The origin of genetic systems is the central problem in the study of the origin of life for which various explanatory hypotheses have been presented....     

Flower biology of the cactus Coryphantha elephantidens in the tropical dry forest of Central Mexico

Floral traits and sexual systems in angiosperms are strategies that enhance outcrossing within hermaphrodite flowers and among individuals in a population. Sexual systems with unisexual flowers have also evolved among angiosperms, resulting in sex specialization. Furthermore, the interaction of floral traits and floral visitors determines successful plant reproduction. Globose cacti are bee pollinated, and variation in the diversity of their pollinator assemblages is strongly associated with floral phenotype. Our objective was to describe the floral biology of the cactus Coryphantha elephantidens and to determine its relationship with pollinators. Floral traits were studied by direct observations in live and fixed flowers. The breeding system was determined using two estimators based on floral morphology: pollen grains to ovules per flower (P/O) ratio and outcrossing index. Pollination treatments were conducted to determine the mating system. Floral visitors were recorded using direct observation. Flowers of C. elephantidens are variable in color, protandric, herkogamous and nectarless. Estimators of the breeding system indicated xenogamy, which is consistent with the obligate outcrossing revealed by the pollination experiment. Thirty-seven percent of the plants have female flowers that do not produce pollen, making this population functionally gynodioecious. Both fruit and seed set were high compared to other globose cacti. Pollinators included eight species of native bees, a more diverse pollinator assemblage than other globose cacti. Given the high pressure on pollen due to functional gynodioecy, nectarless flowers, an outcrossing mating system, and the necessity of pollinators to set seeds, we concluded that native bees are highly efficient pollinators that play a crucial role in the sexual reproduction of C. elephantidens.