Influence of Pluchea lanceolata (Asteraceae) on selected soil properties

Allelopathic interference may operate simultaneously, sequentially, and/or in combination with other mechanisms of interference such as nutrient interference. It is hypothesized that under field conditions, allelopathic plants may cause changes in chemical characteristics of soils in addition to qualitative and quantitative changes in the allelochemical status of soil infested with the allelopathic plant. To test this hypothesis, the perennial allelopathic weed Pluchea lanceolata was selected. A comparative study of P. lanceolata-infested soils, and soils 10, 20, 30, and 40 m away from the weed was undertaken to examine soil characteristics and quantitative and qualitative variation in soil phenolics. Impact of seasonal weather on the biotic and chemical characteristics of P. lanceolata, and quantitative variation in phenolics of weed-infested soils was also studied. Growth experiments were conducted to study the seasonal impact on allelopathic interference of P. lanceolata toward certain crop plants. Results indicate that P. lanceolata influences soil properties in addition to causing variation in soil phenolics. Two-way tests (i.e., analyzing allelopathic and nutrient interference) should be run regardless of whether one is studying allelopathy or nutrient interference and it is important to test allelopathy in all studies dealing with nutrient interference.     

Early emergence and resource availability can competitively favour natives over a functionally similar invader

Invasive plant species can form dense populations across large tracts of land. Based on these observations of dominance, invaders are often described as competitively superior, despite little direct evidence of competitive interactions with natives. The few studies that have measured competitive interactions have tended to compare an invader to natives that are unlikely to be strong competitors because they are functionally different. In this study, we measured competitive interactions among an invasive grass and two Australian native grasses that are functionally similar and widely distributed. We conducted a pair-wise glasshouse experiment, where we manipulated both biotic factors (timing of establishment, neighbour identity and density) and abiotic factors (nutrients and timing of water supply). We found that the invader significantly suppressed the performance of the natives; but its suppression ability was contingent on resource levels, with pulsed water/low nutrients or continuous watering reducing its competitive effects. The native grasses were able to suppress the performance of the invader when given a 3-week head-start, suggesting the invader may be incapable of establishing unless it emerges first, including in its own understorey. These findings provide insight for restoration, as the competitive effect of a functionally similar invader may be reduced by altering abiotic and biotic conditions in favour of natives.     

The evolutionary ecology of biotic association in a megadiverse bivalve superfamily: sponsorship required for permanent residency in sediment

Background

Marine lineage diversification is shaped by the interaction of biotic and abiotic factors but our understanding of their relative roles is underdeveloped. The megadiverse bivalve superfamily Galeommatoidea represents a promising study system to address this issue. It is composed of small-bodied clams that are either free-living or have commensal associations with invertebrate hosts. To test if the evolution of this lifestyle dichotomy is correlated with specific ecologies, we have performed a statistical analysis on the lifestyle and habitat preference of 121 species based on 90 source documents.

Methodology/Principal Findings

Galeommatoidea has significant diversity in the two primary benthic habitats: hard- and soft-bottoms. Hard-bottom dwellers are overwhelmingly free-living, typically hidden within crevices of rocks/coral heads/encrusting epifauna. In contrast, species in soft-bottom habitats are almost exclusively infaunal commensals. These infaunal biotic associations may involve direct attachment to a host, or clustering around its tube/burrow, but all commensals locate within the oxygenated sediment envelope produced by the host’s bioturbation.

Conclusions/Significance

The formation of commensal associations by galeommatoidean clams is robustly correlated with an abiotic environmental setting: living in sediments (). Sediment-dwelling bivalves are exposed to intense predation pressure that drops markedly with depth of burial. Commensal galeommatoideans routinely attain depth refuges many times their body lengths, independent of siphonal investment, by virtue of their host’s burrowing and bioturbation. In effect, they use their much larger hosts as giant auto-irrigating siphon substitutes. The evolution of biotic associations with infaunal bioturbating hosts may have been a prerequisite for the diversification of Galeommatoidea in sediments and has likely been a key factor in the success of this exceptionally diverse bivalve superfamily.     

Current genetic research on groundnut in India

The progress in genetic improvement of groundnut in India during the last five decades has been possible largely due to understanding and utilizing the information generated on the genetics of various characters of the plant. The current genetic studies on groundnut in India are carried out both on qualitative and agronomically important quantitative characters. Research accomplishments which are noteworthy in these areas have been reported in this paper. However, the genetics of several characters of economic importance has not been analyzed so far. Efforts to incorporate resistance to abiotic and biotic factors have gained momentum and a large number of resistant sources have been identified for each of these constraints. Additional efforts are expected to be made on gaining insight into the genetics of resistance to abiotic stresses and insect pests among biotic stresses, where the available information is meagre. Future studies are also expected to concentrate on unravelling the relationship of economic yield with various other characters, including the physiological and biochemical ones. Molecular marker techniques hold promise for genetic analysis of groundnut, as in other crop plants.     

Gene expression, cellular diversification and tumor progression to the metastatic phenotype.

Alterations in the expression of certain genes or in their products can render benign tumor cells metastatic. Experimentally this has been quickly performed by transferring dominantly acting oncogenes such as c-H-rasEJ into susceptible cells, but in vivo such a rapid qualitative change in a dominantly acting oncogene occurs only rarely, and progression to highly metastatic phenotypes is thought to occur through a slow stepwise process. Such slow changes can be reversible and need not involve known dominantly acting oncogenes, consistent with clinical observations. An important element of the natural progression of tumors to malignancy may be their ability to circumvent microenvironmental controls that regulate growth and cellular diversity and to evolve into heterogeneous phenotypes, a process that appears to involve mainly quantitative changes in gene expression but which can be rapidly stimulated in cell culture by the introduction of a dominantly acting oncogene. It is proposed that the highly malignant cells that have slowly evolved in vivo with only a few qualitative gene changes have undergone extensive cycles of diversification and accumulation of quantitative changes in the expression of genes that encode products that are related to malignancy and metastasis. Thus, highly malignant cellular phenotypes can arise quickly through specific qualitative changes in critical controlling genes or more slowly by less critical qualitative genetic changes, coupled with cellular diversification and accumulation of quantitative changes in gene expression.     

Cobalamin and microbial plankton dynamics along a coastal to offshore transect in the Eastern North Atlantic Ocean

Cobalamin (B12) is an essential cofactor that is exclusively synthesized by some prokaryotes while many prokaryotes and eukaryotes require an external supply of B12. The spatial and temporal availability of B12 is poorly understood in marine ecosystems. Field measurements of B12 along with a large set of ancillary biotic and abiotic factors were obtained during three oceanographic cruises in the NW Iberian Peninsula, covering different spatial and temporal scales. B12 concentrations were remarkably low (<1.5 pM) in all samples, being significantly higher at the subsurface Eastern North Atlantic Central Water than at shallower depths, suggesting that B12 supply in this water mass is greater than demand. Multiple regression models excluded B12 concentration as predictive variable for phytoplankton biomass or production, regardless of the presence of B12-requiring algae. Prokaryote production was the best predictor for primary production, and eukaryote community composition was better correlated with prokaryote community composition than with nutritional resources, suggesting that biotic interactions play a significant role in regulating microbial communities. Interestingly, co-occurrence network analyses based on 16S and 18S rRNA sequences allowed the identification of significant associations between potential B12 producers and consumers (e.g. Thaumarchaeota and Dynophyceae, or Amylibacter and Ostreococcus respectively), which can now be investigated using model systems in the laboratory.     

Using near-isogenic barley lines to validate deoxynivalenol (DON) QTL previously identified through association analysis

Fusarium head blight (FHB) and its associated mycotoxin, deoxynivalenol (DON), are the major biotic factors limiting cereal production in many parts of the world. A recent association mapping (AM) study of US six-row spring barley identified several modest effect quantitative trait loci (QTL) for DON and FHB. To date, few studies have attempted to verify the results of association analyses, particularly for complex traits such as DON and FHB resistance in barley. While AM methods use measures to control for the effects of population structure and multiple testing, false positive associations may still occur. A previous AM study used elite breeding germplasm to identify QTL for FHB and DON. To verify the results of that study, we evaluated the effects of the nine DON QTL using near-isogenic lines (NILs). We created families of contrasting homozygous haplotypes from lines in the original AM populations that were heterozygous for the DON QTL. Seventeen NIL families were evaluated for FHB and DON in three field experiments. Significant differences between contrasting NIL haplotypes were detected for three QTL across environments and/or genetic backgrounds, thereby confirming QTL from the original AM study. Several explanations for those QTL that were not confirmed are discussed, including the effect of genetic background and incomplete sampling of relevant haplotypes.     

A New Statistical Method for Mixed Variates Analysis in Epidemiological Research

Epidemiologically oriented research often may not do without observational or only partially controlled studies. In many such situations both qualitative characteristics and quantitative ones are observed. In literature there are different methods of handling such problems. The paper presents a method for analyzing dependencies resp. associations between random variates of any kind. The model concerned fullfills the whole field between analysis of variance, analysis of covariance and contingency table analysis. The method is named MIVA or mixed variates analysis, bases on the class of Conditional Gaussian Distributions of the exponential family and results in a unique system of mixed and unmixed measures of association–of pairwise, partial, multiple and global type. These measures are easy to be estimated and tested on significant deviation from zero. They may be used describing or analyzing dependence structures in many epidemiological studies but also in other fields.     

The Importance of Biotic vs. Abiotic Drivers of Local Plant Community Composition Along Regional Bioclimatic Gradients

We assessed if the relative importance of biotic and abiotic factors for plant community composition differs along environmental gradients and between functional groups, and asked which implications this may have in a warmer and wetter future. The study location is a unique grid of sites spanning regional-scale temperature and precipitation gradients in boreal and alpine grasslands in southern Norway. Within each site we sampled vegetation and associated biotic and abiotic factors, and combined broad- and fine-scale ordination analyses to assess the relative explanatory power of these factors for species composition. Although the community responses to biotic and abiotic factors did not consistently change as predicted along the bioclimatic gradients, abiotic variables tended to explain a larger proportion of the variation in species composition towards colder sites, whereas biotic variables explained more towards warmer sites, supporting the stress gradient hypothesis. Significant interactions with precipitation suggest that biotic variables explained more towards wetter climates in the sub alpine and boreal sites, but more towards drier climates in the colder alpine. Thus, we predict that biotic interactions may become more important in alpine and boreal grasslands in a warmer future, although more winter precipitation may counteract this trend in oceanic alpine climates. Our results show that both local and regional scales analyses are needed to disentangle the local vegetation-environment relationships and their regional-scale drivers, and biotic interactions and precipitation must be included when predicting future species assemblages.     

A population based twin study of sex differences in depressive symptoms.

Depressive symptoms reflect depressed mood over a relatively short period of time and are measured using symptom checklists such as the SCL-90. There is some evidence that depressive symptoms are associated with major depression (MD), which is a clinically diagnosed psychiatric illness. Genetic studies of depressive symptomatology suggest a role for genetic factors as well as unique environmental influences. While epidemiological research suggests that depressive symptoms may be influenced by sex-specific factors, few genetically informative findings support this result entirely. We used data from male and female same sex and opposite-sex twin pairs to assess the extent to which genetic, shared and unique environmental factors influence depressive symptoms. Furthermore, we tested for the presence of qualitative and quantitative sex differences in depressive symptoms. Our results suggest that similar to other studies, depressive symptomatology is moderately heritable (31%) with no evidence for shared environmental factors. Our best fitting model suggests that there are no qualitative or quantitative sex differences in depressive symptoms. Our analyses suggest that while there may be mean differences in the levels of depressive symptoms across sexes, the genetic and environmental factors that predispose males and females to depressive symptoms are not different.     

Inducible direct plant defense against insect herbivores: A review

Plants respond to insect herbivory with responses broadly known as direct defenses, indirect defenses, and tolerance. Direct defenses include all plant traits that affect susceptibility of host plants by themselves. Overall categories of direct plant defenses against insect herbivores include limiting food supply, reducing nutrient value, reducing preference, disrupting physical structures, and inhibiting chemical pathways of the attacking insect. Major known defense chemicals include plant secondary metabolites, protein inhibitors of insect digestive enzymes, proteases, lectins, amino acid deaminases and oxidases. Multiple factors with additive or even synergistic impact are usually involved in defense against a specific insect species, and factors of major importance to one insect species may only be of secondary importance or not effective at all against another insect species. Extensive qualitative and quantitative high throughput analyses of temporal and spatial variations in gene expression, protein level and activity, and metabolite concentration will accelerate not only the understanding of the overall mechanisms of direct defense, but also accelerate the identification of specific targets for enhancement of plant resistance for agriculture.     

植物诱导性直接防御

众所周知,植物对植食性昆虫危害的反应表现在3个方面：直接防御,间接防御,和耐害性。直接防御是指植物自身所具有的能影响寄主植物感虫性的所有特性。植物对昆虫危害的直接防御包括：限制食物供给,降低营养价值,减少偏嗜程度,破坏组织结构和抑制害虫代谢途径。目前已知的防御化合物主要包括植物次生代谢物质、昆虫消化酶（蛋白）抑制剂、蛋白酶、凝集素、氨基酸脱氨酶和氧化酶。植物在防御某种昆虫为害时多个因素往往具有累加效应或协同作用,并且对一种昆虫起主导作用的因素在防御另一种昆虫时可能仅仅起次要作用甚至根本不起作用。因此,对寄主植物基因表达、蛋白水平和活性以及代谢物含量在不同时空条件下进行广泛的定量和定性的高通量分析,不仅可以促进对植物直接防御机制的全面理解,而且有助于在农业生产中加快对作物抗性的特定靶标的鉴定。     

The effects of hybridization in plants on secondary chemistry: implications for the ecology and evolution of plant-herbivore interactions

Natural hybridization is a frequent phenomenon in plants. It can lead to the formation of new species, facilitate introgression of plant traits, and affect the interactions between plants and their biotic and abiotic environments. An important consequence of hybridization is the generation of qualitative and quantitative variation in secondary chemistry. Using the literature and my own results, I review the effects of hybridization on plant secondary chemistry, the mechanisms that generate patterns of chemical variation, and the possible consequences of this variation for plants and herbivores. Hybrids are immensely variable. Qualitatively, hybrids may express all of the secondary chemicals of the parental taxa, may fail to express certain parental chemicals, or may express novel chemicals that are absent in each parent. Quantitatively, concentrations of parental chemicals may vary markedly among hybrids. There are five primary factors that contribute to variation: parental taxa, hybrid class (F(1), F(2), etc.), ploidy level, chemical class, and the genetics of expression (dominance, recessive vs. additive inheritance). This variation is likely to affect the process of chemical diversification, the potential for introgression, the likelihood that hybrids will facilitate host shifts by herbivores, and the conditions that might lead to enhanced hybrid susceptibility and lower fitness.     

Neuronal Control of Mucus Secretion by Leeches: Toward a General Theory for Serotonin

The large Retzius cells are serotonin-containing neurons whoseimpulse activity controls the secretion of mucus from the skinof leeches. Serotonin elicits the secretion of mucus withoutany apparent synaptic transfers in either the central or peripheralnervous systems. Such a secretogogue function may be more generalas serotonin controls the secretion of mucus from the gastrointestinaltract of mammals and from the ciliated gills of bivalved molluscs.Furthermore, the qualitative and quantitative distribution ofserotonin in molluscs, annelids, arthropods, and vertebratescorresponds approximately with mucosecretory structures. Serotoninappears also to control other secretory functions in some ofthese animals. It is proposed therefore that serotonin mightoften function in controlling secretion.     

Biotic replacement and mass extinction of the Ediacara biota

The latest Neoproterozoic extinction of the Ediacara biota has been variously attributed to catastrophic removal by perturbations to global geochemical cycles, ‘biotic replacement’ by Cambrian-type ecosystem engineers, and a taphonomic artefact. We perform the first critical test of the ‘biotic replacement’ hypothesis using combined palaeoecological and geochemical data collected from the youngest Ediacaran strata in southern Namibia. We find that, even after accounting for a variety of potential sampling and taphonomic biases, the Ediacaran assemblage preserved at Farm Swartpunt has significantly lower genus richness than older assemblages. Geochemical and sedimentological analyses confirm an oxygenated and non-restricted palaeoenvironment for fossil-bearing sediments, thus suggesting that oxygen stress and/or hypersalinity are unlikely to be responsible for the low diversity of communities preserved at Swartpunt. These combined analyses suggest depauperate communities characterized the latest Ediacaran and provide the first quantitative support for the biotic replacement model for the end of the Ediacara biota. Although more sites (especially those recording different palaeoenvironments) are undoubtedly needed, this study provides the first quantitative palaeoecological evidence to suggest that evolutionary innovation, ecosystem engineering and biological interactions may have ultimately caused the first mass extinction of complex life.     

Plant root growth, architecture and function

Without roots there would be no rhizosphere and no rhizodeposition to fuel microbial activity. Although micro-organisms may view roots merely as a source of carbon supply this belies the fascinating complexity and diversity of root systems that occurs despite their common function. Here, we examine the physiological and genetic determinants of root growth and the complex, yet varied and flexible, root architecture that results. The main functions of root systems are also explored including how roots cope with nutrient acquisition from the heterogeneous soil environment and their ability to form mutualistic associations with key soil micro-organisms (such as nitrogen fixing bacteria and mycorrhizal fungi) to aid them in their quest for nutrients. Finally, some key biotic and abiotic constraints on root development and function in the soil environment are examined and some of the adaptations roots have evolved to counter such stresses discussed.     

The Complexity of Factors Driving Volatile Organic Compound Emissions by Plants

The emissions of volatile organic compounds, VOC, from plants have strong relevance for plant physiology, plant ecology, and atmospheric chemistry. We report here on the current knowledge of the many internal (genetic and biochemical) and external (abiotic - temperature, light, water availability, wind, ozone, and biotic - animal, plant and microorganisms interactions) factors that control emission rates of different VOC by altering their synthesis, vapour pressure or diffusion to the atmosphere. The complex net of these factors, their interactions and the different responses of the different VOC produces the large qualitative and quantitative, spatial and temporal variability of emissions and the frequent deviations from current standard emission models. The need for a co-operative multidisciplinary multiscale research to disentangle this complex and important issue of plant VOC emissions is reminded.