Phoma Leaf Spot Disease of Tinospora Cordifolia and its Effect on Secondary Metabolite Production

Tinospora cordifolia is one of the important medicinal climbers growing extensively in Bhadra Wildlife Sanctuary, Karnataka, India. The plant foliages were found infected with Phoma putaminum in different parts of the sanctuary. A three‐year (August 2006–July 2009) study of the disease due to the pathogen indicated that the disease incidence (DI) ranged from 0 to 100% (maximum in Kakanahasudi), while disease severity (DS) ranged from 1.60 to 45.00% (maximum in Madhuguni). The environmental parameters like rainfall and relative humidity (RH) correlated significantly with DI and DS, while temperature correlated negatively. The regression analysis indicated that DI and DS were affected due to increase in RH and decrease in temperature and rainfall. The spatial heterogeneity of the foliar disease determined by the binary form of modified Taylor's power law indicated that the disease incidence showed the regular pattern of dispersion (P < 0.001) in seven forest regions and heterogenous pattern (P < 0.001) in one forest region. The result also indicated that the alkaloid content decreased drastically following infection with P. putaminum, while phenol, flavonoid and steroid contents increased with increase in the severity of infection.     

Driving factors of small-scale variability in a savanna plant population after a fire

The severity of fire impacts on fire-prone vegetation is often spatially heterogeneous, and may lead to small-scale patchiness in the structure of plant populations by affecting mortality, topkill, and reproduction. This patchiness, however, is not usually taken into account in fire ecology studies. We show that a dry-season fire may result in small-scale patchiness in the population structure of the common shrub Miconia albicans, mostly by differential topkill and resprouting. We related fire severity to population structure parameters of the study species and assessed the effects of fire on its soil seed bank. Basal area of non-woody live stems and of dead stems increased with fire severity, whereas that of woody live stems decreased, indicating topkill and resprouting. However, there was no relationship between fire severity and the total number of live or dead plants, showing that mortality in the fire was low. We found very few seedlings, indicating that resprouting, not germination from the soil seed bank, is the main recovery strategy of this species. The fire also affected the soil seed bank, as there were fewer seedlings emerging from soil collected in burned patches. Although this study was performed with a single species, it is likely that other species, especially those with basal resprouting, will show similar patterns of post-fire patchiness in population structure. This patchiness, in turn, may affect the spatial distribution of future fires, and should be taken into account in studies of fire ecology.     

Mapping landscape services,spatial synergies and trade-offs. A case study using variogram models and geostatistical simulations in an agrarian landscape in North-East Germany

This paper presents a probabilistic approach for mapping and assessment of services provided by landscapes, based on variogram modelling and geostatistical simulations. Of operational value is that several services can be treated and mapped simultaneously, providing an efficient tool to model the heterogeneity of different landscape components. The methodology was adopted to depict spatial heterogeneity of five landscape services in the case study area of Märkische Schweiz in North East Germany: habitat for species, crop production, visual appreciation, water supply, and water regulation. Results, displayed in terms of single and joint probability maps, provide new insights about the composition and interrelation of multiple services in a region. It is shown that each landscape service is characterised by a specific spatial pattern, described in terms of heterogeneity and spatial range. Setting a probability threshold of service occurrence >0.50, 10% of the area under agricultural land uses provides no landscape services, 35% delivers one service while 25% and 19% supply two and three services, respectively. The share of agricultural area with a potential joint provision of four services equals 10%, while only 1.4% of the area has a potential to deliver five joint landscape services. The highest mean join probability is that observed for the common supply of production and habitat services (30%), highlighting the occurrence of hotspots of services provision with possible conflicts due to the on-going intensification of agricultural management.     

AliGROOVE – visualization of heterogeneous sequence divergence within multiple sequence alignments and detection of inflated branch support

Background

Masking of multiple sequence alignment blocks has become a powerful method to enhance the tree-likeness of the underlying data. However, existing masking approaches are insensitive to heterogeneous sequence divergence which can mislead tree reconstructions. We present AliGROOVE, a new method based on a sliding window and a Monte Carlo resampling approach, that visualizes heterogeneous sequence divergence or alignment ambiguity related to single taxa or subsets of taxa within a multiple sequence alignment and tags suspicious branches on a given tree.

Results

We used simulated multiple sequence alignments to show that the extent of alignment ambiguity in pairwise sequence comparison is correlated with the frequency of misplaced taxa in tree reconstructions. The approach implemented in AliGROOVE allows to detect nodes within a tree that are supported despite the absence of phylogenetic signal in the underlying multiple sequence alignment. We show that AliGROOVE equally well detects heterogeneous sequence divergence in a case study based on an empirical data set of mitochondrial DNA sequences of chelicerates.

Conclusions

The AliGROOVE approach has the potential to identify single taxa or subsets of taxa which show predominantly randomized sequence similarity in comparison with other taxa in a multiple sequence alignment. It further allows to evaluate the reliability of node support in a novel way.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2105-15-294) contains supplementary material, which is available to authorized users.     

Intermediate fragmentation per se provides stable predator-prey metapopulation dynamics

The extent to which a landscape is fragmented affects persistence of predator-prey dynamics. Increasing fragmentation concomitantly imposes conditions that stabilise and destabilise metapopulations. For the first time, we explicitly assessed the hypothesis that intermediate levels provide optimal conditions for stability. We examine four structural changes arising from increased fragmentation: increased fragment number; decreased fragment size; increased connectedness (corridors scaled to fragment); increased fragment heterogeneity (based on connectedness). Using the model predator-prey system (Didinium-Paramecium) we support our hypothesis, by examining replicated metapopulations dynamics at five fragmentation levels. Although both species became extinct without fragmentation, prey survived at low and high levels, and both survived at intermediate levels. By examining time to extinction, maximum abundances, and population asynchrony we conclude that fragmentation produces structural heterogeneity (independent of environmental heterogeneity), which influences stability. Our analysis suggests why some theoretical, field and microcosm studies present conflicting views of fragmentation effects on population persistence.     

Environment-dependent selection on mate choice in a natural population of birds

Female mate choice acts as an important evolutionary force, yet the influence of the environment on both its expression and the selective pressures acting upon it remains unknown. We found consistent heritable differences between females in their choice of mate based on ornament size during a 25-year study of a population of collared flycatchers. However, the fitness consequences of mate choice were dependent on environmental conditions experienced whilst breeding. Females breeding with highly ornamented males experienced high relative fitness during dry summer conditions, but low relative fitness during wetter years. Our results imply that sexual selection within a population can be highly variable and dependent upon the prevailing weather conditions experienced by individuals.     

Spatial heterogeneity in the strength of selection against deleterious alleles and the mutation load

According to current estimates of genomic deleterious mutation rates (which are often of the order 0.1-1) the mutation load (defined as a reduction in the average fitness of a population due to the presence of deleterious alleles) may be important in many populations. In this paper, I use multilocus simulations to explore the effect of spatial heterogeneity in the strength of selection against deleterious alleles on the mutation load (for example, it has been suggested that stressful environments may increase the strength of selection). These simulations show contrasted results: in some situations, spatial heterogeneity may greatly reduce the mutation load, due to the fact that migrants coming from demes under stronger selection carry relatively few deleterious alleles, and benefit from a strong advantage within demes under weaker selection (where individuals carry many more deleterious alleles); in other situations, however, deleterious alleles accumulate within demes under stronger selection, due to migration pressure from demes under weaker selection, leading to fitness erosion within those demes. This second situation is more frequent when the productivity of the different demes is proportional to their mean fitness. The effect of spatial heterogeneity is greatly reduced, however, when the response to environmental differences is inconsistent across loci.