The effect of zinc contamination from electricity pylons. Genetic constraints on selection for zinc tolerance

Recent Progress, Challenges, and Opportunities of Membrane Distillation for Heavy Metals Removal

Water is essential for the presence of life on this earth. However, water contamination due to the presence of heavy/toxic metals is one of the serious environmental issues for living beings. Several methods have been devoted to separating or removing those heavy metals from wastewater. Among them, membrane distillation (MD) has become one of the most attractive approaches due to its higher rejection rate than processes driven by pressure, lower energy consumption than traditional distillation processes. MD has gained significant attention for removing heavy metals than other techniques like ion exchange and adsorption in the last two decades. This review provides insight knowledge to the reader and focuses on how heavy metals impact humans and the environment, sources of heavy metals, current and especially removal methods using the MD method. Moreover, recent studies, challenges, and opportunities on MD membrane modules and heavy metal removal systems are discussed. More importantly, in this review, we have identified the gaps and opportunities that are required for enhancing the MD approach and its practical suitability for heavy metal removals. MD module and system showed high performance, proving their possible applications to remove heavy metal ions in water/wastewater treatment.

Additive genetic variance for lifetime fitness and the capacity for adaptation in an annual plant

The immediate capacity for adaptation under current environmental conditions is directly proportional to the additive genetic variance for fitness, V_A (W). Mean absolute fitness, W ¯ , is predicted to change at the rate V A ( W ) W ¯ , according to Fisher's Fundamental Theorem of Natural Selection. Despite ample research evaluating degree of local adaptation, direct assessment of V_A (W) and the capacity for ongoing adaptation is exceedingly rare. We estimated V_A (W) and W ¯ in three pedigreed populations of annual Chamaecrista fasciculata, over three years in the wild. Contrasting with common expectations, we found significant V_A (W) in all populations and years, predicting increased mean fitness in subsequent generations (0.83 to 6.12 seeds per individual). Further, we detected two cases predicting "evolutionary rescue," where selection on standing V_A (W) was expected to increase fitness of declining populations ( W ¯ < 1.0) to levels consistent with population sustainability and growth. Within populations, inter-annual differences in genetic expression of fitness were striking. Significant genotype-by-year interactions reflected modest correlations between breeding values across years, indicating temporally variable selection at the genotypic level that could contribute to maintaining V_A (W). By directly estimating V_A (W) and total lifetime W ¯ , our study presents an experimental approach for studies of adaptive capacity in the wild.

Assessment of genetic diversity, population structure and sex identification in dioecious crop, Trichosanthes dioica employing ISSR, SCoT and SRAP markers

Twenty inter-simple sequence repeat (ISSR) and twenty two start codon targeted (SCoT) primers were employed to analyze genetic diversity and population structure among 52 Trichosanthes dioica Roxb. accessions collected from nine different eco-geographical regions of India. ISSR markers proved to be more informative in genetic diversity assessment and produced higher mean number of polymorphic bands (15.25 with 95.96% polymorphism) and polymorphic information content (PIC) value (0.47) compared to SCoT markers (12.55 polymorphic bands with 92.20% polymorphism and PIC: 0.45). Total genetic diversity (Ht) and genetic diversity within populations (Hs) in T. dioica accessions was found to be very high (0.45 and 0.43, respectively). AMOVA analysis also revealed higher genetic variation within populations (81%) than among them (19%). Among different T. dioica populations, very low genetic differentiation (Gst: 0.05) and high gene flow (Nm: 9.32) were observed. T. dioica populations of Bihar state were found to be highly diverse and Kolkata and Cuttack populations were least diverse. T. dioica male plants were more variable than females. UPGMA, Neighbor-Joining and population structure analyses divided T. dioica populations into three main clusters. First cluster comprised of Meerut population, second cluster included of Cuttack and Kolkata populations and populations of Bihar, Delhi and Kanpur occurred in third cluster. Genetic diversity was found to be strongly positively correlated with the latitude and strongly negatively correlated with annual mean rainfall of different T. dioica cultivated regions. For sex identification, one SRAP primer combination, 'Em-6/Me-4' amplified two molecular markers of around 230 and 290 bp specific to male T. dioica plants of Bihar, Kanpur, North Delhi and Meerut populations and were completely absent from female plants.

Geography Plays a More Important Role than Soil Composition on Structuring Genetic Variation of Pseudometallophyte Commelina communis

Pseudometallophytes are excellent models to study microevolution and local adaptation to soil pollution, as they can grow both on metalliferous and contrasting non-metalliferous soils. Although, there has been accumulating evidence for the effects of edaphic conditions and geographical isolation on the genetic structure of pesudometallophytes, it is still a difficult problem in evolutionary biology to assess their relative importance. In this study, we investigated the spatial patterns of genetic variability, population differentiation and genetic groups in pseudometallophyte Commelina communis with 12 microsatellite loci. Eight metallicolous and six non-metallicolous populations of C. communis were sampled from cupriferous sites and surrounding non-contaminated areas in China. Neither significant reduction in genetic diversity nor apparent founder and bottleneck effects were observed in metallicolous populations of C. communis. Based on Bayesian and Neighbor-Joining clustering analyses and a principal coordinates analysis, all sampled populations were found to be mainly separated into three genetic groups, corresponding well to their geographical locations rather than edaphic origins. Moreover, a significant and strong correlation between population genetic divergence and geographical distance were detected by Mantel test (r = 0.33; P < 0.05) and multiple matrix regression with randomization (MMRR; βD = 0.57, P < 0.01). However, the effect of copper concentration on genetic patterns of C. communis was not significant (MMRR; βE = -0.17, P = 0.12). Our study clearly demonstrated that the extreme edaphic conditions in metalliferous areas had limited effects on the genetic variability in C. communis. Geographic distance played a more important role in affecting the genetic structure of C. communis than soil composition did. In C. communis, the geographically disjunctive populations on metalliferous soils had multiple origins and evolved independently from nearby non-metallicolous populations.

An ideal weed: plasticity and invasiveness in Polygonum cespitosum

The introduced Asian plant Polygonum cespitosum has only recently become invasive in northeastern North America, spreading into sunny as well as shaded habitats. We present findings from a multiyear case study of this ongoing species invasion, drawing on field environmental measurements, glasshouse plasticity and resurrection experiments, and molecular genetic (microsatellite) data. We focus in particular on patterns of individual phenotypic plasticity (norms of reaction), their diversity within and among populations in the species' introduced range, and their contribution to its potential to evolve even greater invasiveness. Genotypes from introduced-range P. cespitosum populations have recently evolved to express greater adaptive plasticity to full sun and/or dry conditions without any loss of fitness in shade. Evidently, this species may evolve the sort of "general-purpose genotypes" hypothesized by Herbert Baker to characterize an "ideal weed." Indeed, we identified certain genotypes capable of extremely high reproductive output across contrasting conditions, including sunny, shaded, moist, and dry. Populations containing these high-performance genotypes had consistently higher fitness in all glasshouse habitats; there was no evidence for local adaptive differentiation among populations from sunny, shaded, moist, or dry sites. Norm of reaction data may provide valuable insights to invasion biology: the presence of broadly adaptive, high-performance genotypes can promote a species' ecological spread while providing the fuel for increased invasiveness to evolve.

Assessment of genetic diversity in the endangered populations of Breonadia salicina (Rubiaceae) growing in the kingdom of Saudi Arabia using inter-simple sequence repeat markers

BACKGROUND

Breonadia salicina (Rubiaceae) is a critically endangered plant at the local scale native to southwestern Saudi Arabia. To understand the levels and partitioning of genetic variation across populations and geographical regions of this species, we assessed its genetic diversity using inter-simple sequence repeat (ISSR) markers.

RESULTS

Fourteen ISSR primers selected from 43 primers gave rise to 211 amplified loci, of which 68 were polymorphic. The percentage of polymorphic loci (PPL) at the population level ranged from 17.1 to 23.7%, with an average of 21.3%. Nei's gene diversity (h) and Shannon's information index (I) were 0.086 and 0.125, respectively. At the species level, PPL was 32.2%, while h and I were 0.116 and 0.172, respectively. A hierarchical analysis of molecular variance revealed a high level of genetic differentiation among populations (17% of total variance, P = 0.001), consistent with the gene differentiation coefficient (G ST = 0.256). Nevertheless, the evaluated genetic diversity was very low within populations; while relatively high among populations, levels were insufficient for long-term survival. Saudi Arabian accessions were also compared to accessions of a population from Yemen, where the species is more widespread. The Yemeni population also showed low genetic diversity but clustered separately.

CONCLUSIONS

Breonadia salicina in Saudi Arabia is characterized by low within-population genetic diversity and high among-population genetic differentiation. Based on our findings, this locally endangered species is on the verge of local extinction. The species' survival depends on successful implementation of suggested strategies for its long-term conservation.

Propagule limitation, disparate habitat quality, and variation in phenotypic selection at a local species range boundary

Adaptation to novel conditions beyond current range boundaries requires the presence of suitable sites within dispersal range, but may be impeded when emigrants encounter poor habitat and sharply different selection pressures. We investigated fine-scale spatial heterogeneity in ecological dynamics and selection at a local population boundary of the annual plant Gilia tricolor. In two years, we planted G. tricolor seeds in core habitat, margin habitat at the edge of the local range, and exterior habitat in order to measure spatial and temporal variation in habitat quality, opportunity for selection, and selection on phenotypic traits. We found a striking decline in average habitat quality with distance from the population core, yet some migrant seeds were successful in suitable, unoccupied microsites at and beyond the range boundary. Total and direct selection on four out of five measured phenotypic traits varied across habitat zones, as well as between years. Moreover, the margin habitat often exerted unique selection pressures that were not intermediate between core and exterior habitats. This study reveals that a combination of ecological and evolutionary forces, including propagule limitation, variation in habitat quality and spatial heterogeneity in phenotypic selection may reduce opportunities for adaptive range expansion, even across a very local population boundary.

Metal resistance in populations of red maple (Acer rubrum L.) and white birch (Betula papyrifera Marsh.) from a metal-contaminated region and neighbouring non-contaminated regions

Metal resistance in populations of Acer rubrum and Betula papyrifera in the industrially contaminated region of Sudbury, Ontario, was compared with resistance in populations from neighbouring uncontaminated regions. In two one-season experiments, seedlings were grown outdoors on contaminated (mainly Cu, Ni) and uncontaminated substrates. Sudbury populations of both species responded less to contamination than populations from uncontaminated regions. In A. rubrum this difference was small. For both species, Sudbury plants were smaller when grown on uncontaminated substrate. B. papyrifera from Sudbury grew better on contaminated substrate than the other populations. There is indication of variation in metal resistance within the populations from the non-contaminated regions. The data shows that trees may develop adaptive resistance to heavy metals, but the low degree of resistance indicates that the development of such resistances are slower than observed for herbaceous species with shorter generation times.

Parallel Ecological Speciation in Plants?

Populations that have independently evolved reproductive isolation from their ancestors while remaining reproductively cohesive have undergone parallel speciation. A specific type of parallel speciation, known as parallel ecological speciation, is one of several forms of evidence for ecology's role in speciation. In this paper we search the literature for candidate examples of parallel ecological speciation in plants. We use four explicit criteria (independence, isolation, compatibility, and selection) to judge the strength of evidence for each potential case. We find that evidence for parallel ecological speciation in plants is unexpectedly scarce, especially relative to the many well-characterized systems in animals. This does not imply that ecological speciation is uncommon in plants. It only implies that evidence from parallel ecological speciation is rare. Potential explanations for the lack of convincing examples include a lack of rigorous testing and the possibility that plants are less prone to parallel ecological speciation than animals.

Morphological and genetic variations of Potentilla matsumurae (Rosaceae) between fellfield and snowbed populations

Identifying ecological factors associated with local differentiation of populations is important for understanding microevolutionary processes. Alpine environments offer a unique opportunity to investigate the effects of habitat-specific selective forces and gene flow limitations among populations at a microscale on local adaptation because the heterogeneous snowmelt patterns in alpine ecosystems provide steep environmental changes. We investigated the variation in morphological traits and enzyme loci between fellfield and snowbed populations of Potentilla matsumurae, a common alpine herb with a wide distribution along snowmelt gradients in northern Japan. We found significant differences in morphological traits between fellfield and snowbed habitats in a northern distribution region. These differences were maintained when plants were grown under uniform conditions in a greenhouse. Allozyme variations among 15 populations from geographically separated regions with different historical backgrounds showed that the populations are more genetically differentiated between the fellfield and snowbed habitats within a region than between populations occupying the same habitat type in different regions. These results suggest that variation in snowmelt regimes could be a driving force creating local adaptation and genetic differentiation of alpine plant populations.

Evidence of adaptive tolerance to nickel in isolates of Cenococcum geophilum from serpentine soils

Selection for metal-tolerant ecotypes of ectomycorrhizal (ECM) fungi has been reported in instances of metal contamination of soils as a result of human activities. However, no study has yet provided evidence that natural metalliferous soils, such as serpentine soils, can drive the evolution of metal tolerance in ECM fungi. We examined in vitro Ni tolerance in isolates of Cenococcum geophilum from serpentine and non-serpentine soils to assess whether isolates from serpentine soils exhibited patterns consistent with adaptation to elevated levels of Ni, a typical feature of serpentine. A second objective was to investigate the relationship between Ni tolerance and specific growth rates (micro) among isolates to increase our understanding of possible tolerance/growth trade-offs. Isolates from both soil types were screened for Ni tolerance by measuring biomass production in liquid media with increasing Ni concentrations, so that the effective concentration of Ni inhibiting fungal growth by 50% (EC(50)) could be determined. Isolates of C. geophilum from serpentine soils exhibited significantly higher tolerance to Ni than non-serpentine isolates. The mean Ni EC(50) value for serpentine isolates (23.4 microg ml(-1)) was approximately seven times higher than the estimated value for non-serpentine isolates (3.38 microg ml(-1)). Although there was still a considerable variation in Ni sensitivity among the isolates, none of the serpentine isolates had EC(50) values for Ni within the range found for non-serpentine isolates. We found a negative correlation between EC(50) and micro values among isolates (r = -0.555). This trend, albeit only marginally significant (P = 0.06), indicates a potential trade-off between tolerance and growth, in agreement with selection against Ni tolerance in "normal" habitats. Overall, these results suggest that Ni tolerance arose among serpentine isolates of C. geophilum as an adaptive response to Ni exposure in serpentine soils.

Strong ecological but weak evolutionary effects of elevated CO2 on a recombinant inbred population of Arabidopsis thaliana

Increases in atmospheric CO2 concentration have an impact on plant communities by influencing plant growth and morphology, species interactions, and ecosystem processes. These ecological effects may be accompanied by evolutionary change if elevated CO2 (eCO2) alters patterns of natural selection or expression of genetic variation. Here, a statistically powerful quantitative genetic experiment and manipulations of CO2 concentrations in a field setting were used to investigate how eCO2 impacts patterns of selection on ecologically important traits in Arabidopsis thaliana; heritabilities, which influence the rate of response to selection; and genetic covariances between traits, which may constrain responses to selection. CO2 had strong phenotypic effects; plants grown in eCO2 were taller and produced more biomass and fruits. Also, significant directional selection was observed on many traits and significant genetic variation was observed for all traits. However, no evolutionary effect of eCO2 was detected; patterns of selection, heritabilities and genetic correlations corresponded closely in ambient and elevated CO2 environments. The data suggest that patterns of natural selection and the quantitative genetic parameters of this A. thaliana population are robust to increases in CO2 concentration and that responses to eCO2 will be primarily ecological.

Functional ecology of ecotypic differentiation in the Californian serpentine sunflower (Helianthus exilis)

* Here, we examined phenotypic differences between locally adapted serpentine and riparian populations of the serpentine sunflower Helianthus exilis from northern California, USA. * Within a common environment, plants from serpentine and riparian sites were grown in regular potting soil or serpentine soil. Physiology, morphology, phenology and fitness-related traits were measured. * Overall, riparian plants grew more rapidly, attained a larger final size, produced larger leaves, and smaller flowering heads. Riparian plants also invested less in root biomass and were more water-use-efficient than the serpentine plants. Serpentine and riparian plants also differed in leaf concentrations of boron, magnesium, sodium and molybdenum. * These ecotypic differences suggest contrasting adaptive strategies to cope with either edaphic stress in serpentine sites or intense above-ground competition at riparian sites. There was a significant population origin x soil type crossing interaction in one fitness trait (average dry weight) that mirrored local adaptation previously documented for these riparian and serpentine ecotypes. However, because all other fitness traits did not exhibit this crossing interaction in our common garden study, it is possible that phenotypic differences underlying local adaptation may be amplified in the field as a result of biotic and abiotic interactions.

Photochemical efficiency is an important component of ecophysiological variation of Cistus albidus between habitats in south-east Spain

The ecophysiology of Cistus albidus L. plants in a variety of habitats in south-east Spain was measured in situ over the course of a year, to determine whether physiological variation occurs between populations growing in sites exposed to differing temperature and precipitation. Not all the observed variation could be explained by differing contemporary meteorological conditions. In particular, plants at the driest site maintained much higher photochemical efficiency through the summer and autumn than plants at the other sites, and also showed higher stomatal conductance after the autumn rains. Principal component analysis identified photochemical efficiency as the greatest source of variation between populations. Such variation may represent the result of differing selection in populations that have been exposed to different prevailing conditions of mean temperature, precipitation or atmospheric humidity, for long periods of time.

AFLP-based assessment of the effects of environmental heavy metal pollution on the genetic structure of pioneer populations of Suillus luteus

•  The effects of environmental heavy metal pollution on the genetic structure of pioneer populations of the ectomycorrhizal basidiomycete Suillus luteus were assessed. •  Sporocarps were collected from nine different locations and characterized by amplified fragment length polymorphism (AFLP) markers. Six of the sampling sites were contaminated with heavy metals and were dominated by tolerant individuals. Considerable genetic diversity was found within geographic subpopulations, but no reduction of the genetic diversity of populations inhabiting contaminated soils was observed. Neither did significant clustering of subpopulations inhabiting contaminated soils occur. Overall, the genetic differentiation between subpopulations was low, but Bayesian inference indicated the presence of two genetically differentiated clusters of individuals, which may correspond to different intercompatibility groups in S. luteus. •  Heavy metal contamination seems to have a limited influence on the genetic structure of populations of S. luteus. Loss of diversity may have been prevented by sexual reproduction and rapid evolution of the tolerance trait or initial genetic bottlenecks may have been reduced by admixture and recurrent migration from surrounding populations colonizing noncontaminated soils.

A zinc-adapted fungus protects pines from zinc stress

•  Here we investigated zinc tolerance of ectomycorrhizal Scots pine (Pinus sylvestris) seedlings. An ectomycorrhizal genotype of Suillus bovinus, collected from a Zn-contaminated site and showing adaptive Zn tolerance in vitro, was compared with a nonadapted isolate from a nonpolluted area. •  A dose-response experiment was performed. Dynamics of plant and fungal development, and phosphate and ammonium uptake capacity, were assessed under increasing Zn stress. Effects of Zn on transpiration, nutrient content and Zn accumulation were analysed. •  Significant Zn-inoculation interaction effects were observed for several responses measured, including uptake rates of phosphate and ammonium; phosphorus, iron and Zn content in shoots; transpiration; biomass of external mycelia; and fungal biomass in roots. •  The Zn-tolerant S. bovinus genotype was particularly efficient in protecting pines from Zn stress. The growth of a Zn-sensitive genotype from a normal wild-type population was inhibited at high Zn concentrations, and this isolate could not sustain the pines' acquisition of nutrients. This study shows that well adapted microbial root symbionts are a major component of the survival strategy of trees that colonize contaminated soils.

Edaphic races and phylogenetic taxa in the Lasthenia californica complex (Asteraceae: Heliantheae): an hypothesis of parallel evolution

Lasthenia californica sensu Ornduff consists of two races that differ in their flavonoid pigments and edaphic tolerances. Recent phylogenetic studies of Lasthenia have revealed that members of L. californica sensu Ornduff belong to two phylogenetic species. The relationship of the edaphic races to these new species and to each other is the focus of this study. Characterization of flavonoid profiles and phylogenetic placement of 33 populations demonstrates that races and phylogenetic taxa are not concordant, suggesting that one or both edaphic races evolved in parallel in the two clades. We hypothesize an edaphically linked ecological role for flavonoid differences that first revealed the existence of two races.

Molecular genecology of temperature response in Lolium perenne: 1. preliminary analysis to reduce false positives

Molecular genecology is the study of geographical clines in frequencies of molecular markers and their relationship to ecological clines in environmental conditions. This study outlines the principles underlying the selection of populations, focusing on avoiding 'false positives'- noncausal correlations between allele frequency and the environment. The principles are illustrated by identifying a set of populations of Lolium perenne for the study of temperature responses. The selected set of populations encompasses a 20 degrees C range in mean January temperature. Their freezing tolerance shows a linear trend with winter temperature, LT50 decreasing by 0.25 degrees C for each 1 degrees C reduction in mean January temperature.

Evolution of herbicide resistance in weeds: initial frequency of target site-based resistance to acetolactate synthase-inhibiting herbicides in Lolium rigidum

The frequency of individuals resistant to two acetolactate synthase (ALS)-inhibiting herbicides in three previously untreated populations of Lolium rigidum was determined. The frequency of individuals resistant to the sulfonylurea herbicide sulfometuron-methyl varied from 2.2 x 10(-5) to 1.2 x 10(-4) and the frequency of individuals resistant to the imidazolinone herbicide imazapyr varied from 1 x 10(-5) to 5.8 x 10(-5) depending on the population. Application of sulfometuron-methyl selected individuals with a herbicide-insensitive ALS, which was also cross-resistant to imazapyr. The high initial frequency of individuals resistant to ALS-inhibiting herbicides in L. rigidumpopulations never previously exposed to these herbicides helps explain the rapid evolution of herbicide resistance in this species once ALS-inhibiting herbicides were used.

The genetics of metal tolerance in vascular plants

In many parts of the world soils are detrimental to plant growth owing to elevated levels of metal ions, caused either by natural processes or by the result of man's activities. Many plants have evolved ecotypes or varieties that are able to grow more-or-less normally on these soils. This paper reviews our knowledge of the genetics of this phenomenon. The nature of tolerance and the problems of its measurement are discussed. Tolerance is frequently measured by an index produced by comparing growth in a contaminated environment with growth in a control environment. It is argued that this measurement is inappropriate for many genetical studies, and that it is frequently more useful to use growth at a single critical level of metal as a measure of tolerance. Polygenic inheritance provides a null hypothesis that has to be tested in a genetical analysis. Examples of major genes for tolerance to aluminium, arsenic, boron, cadmium, copper and manganese are discussed. Even where major genes have been demonstrated, it is probable that other minor genes, 'modifiers', are present as well. Because of the nature of tolerance as a character, dominance and epistasis are likely to vary with the level of metal at which an analysis is performed. Tolerance is generally found to be dominant at some levels of the metal. Studies which have mapped tolerance genes, particularly to aluminium and salt, are discussed. The specificity of tolerance is a matter of some confusion. Some studies indicate that tolerances evolve independently to different metals, but others have suggested that tolerance to one metal may often confer a degree of tolerance to some other metals. Very little is known about the molecular genetics of tolerance, and the mechanisms of tolerance to most metals. The possible role of phytochelatins and metallothionein-like proteins in metal tolerance is discussed. The distribution of tolerance in natural populations suggests that tolerance is a disadvantage in uncontaminated environments, but how this 'cost' arises is not known. There is some evidence that the disadvantage to tolerance may be associated more with the modifiers of tolerance than with the primary tolerance gene. The study of the genetics of tolerance is of importance in planning breeding programmes to produce tolerant crops for use in areas where metal contamination is a limiting factor in productivity. It can also assist in understanding the mechanisms of tolerance, as exemplified by the study of the mechanism of arsenic tolerance in Holcus lanatus. Important areas for further research are discussed. Contents Summary 541 I. Introduction 542 II. Introduction 542 III. Transmission genetics of tolerance 544 IV. Specificity of tolerance 550 V. Molecular genetics of tolerance 552 VI. Ecological genetics of tolerance 553 VII. Conclusions 555 Acknowledgements 556 References 556.