Relationship between plant phosphorus status and the kinetics of arsenate influx in clones ofdeschampsia cespitosa (L.) beauv. that differ in their tolerance to arsenate

Uptake kinetics of arsenate were determined in arsenate tolerant and non-tolerant clones of the grassDeschampsia cespitosa under differing root phosphorus status to investigate the mechanism controlling the suppression of arsenate influx observed in tolerant clones. Influx was always lower in tolerants compared to non-tolerants. Short term influx of arsenate by the high affinity uptake system in both tolerant clones was relatively insensitive to root phosphorus status. This was in contrast to the literature where the regulation of the phosphate (arsenate) uptake system is normally much more responsive to plant phosphorus status. The low affinity uptake system in both tolerant and non-tolerant clones, unlike the high affinity uptake system, was more closely regulated by root phosphate status and was repressed to a much greater degree under increasing root phosphorus levels than the high affinity system.     

Models of parent-offspring conflict. III. Intra-brood conflict

A genetic model of parent-offspring conflict is developed for the situation where conflictors cause the parent to redirect resources from contemporaneous siblings to themselves, by increased solicitation. It is shown that there is no restriction on the spread of genes causing such conflict if there is no direct cost associated with it. We examine the effect of imposing on the conflictors a cost of the extra solicitation when the cost is felt (a) by the individual conflictor only, and (b) by all members of the brood equally. It is shown that the Evolutionarily Stable Strategies for the two situations allow a greater degree of solicitation when its cost is borne by the whole brood. Multipaternity of broods also increases the degree of conflict.     

Why the evolution of resistance to anthropogenic toxins normally involves major gene changes: the limits to natural selection

Standard population genetic theory suggests that adaptation should normally be achieved by the spread of many genes each of small effect (polygenes), and that adaptation by major genes should be unusual. Such models depend on consideration of the rates of acquisition of adaptation. In practice, adaptation to pollutants and anthropogenic toxins has most frequently been achieved by the spread of major genes. A simple model is developed to explain this discrepancy, in which the determining factor is not the rate of spread, but the maximum response achievable under the two contrasting models of polygenic or major gene inheritance. In the short term, for a given mean and genetic variance, characters in which the additive genetic variance is produced by the segregation of many genes of small effect at intermediate gene frequencies are unable to produce as large a response to directional selection as characters in which the variance is caused by genes of large effect at low frequency. If the target for selection is a long way from the mean prior to selection (as it may well be for adaptation to novel anthropogenic stresses) then adaptation can only be achieved by species possessing major genes. The model is discussed with reference to the example of heavy metal tolerance in plants.     

Heavy metal tolerance in plants: A model evolutionary system

Evolved tolerance to toxic concentrations of heavy metals in plants inhabiting spoil heaps of mines is a well known phenomenon that has been the subject of much research in the last two decades. These plants are useful models for studying processes involved in the early stages of the speciation of edaphic endemics. Recent work has revealed the importance of several phenomena in the differentiation of tolerant populations, including natural selection, founder effects and ‘hitch-hiking’, and has demonstrated the early evolution of morphological differentiation and reproductive isolating mechanisms. Further studies of the biochemistry and molecular biology of heavy metal tolerance will help to show why some plant groups, such as Agrostis, are far more prone to evolve tolerance than others.     

Deaths from abuse of volatile substances: a national epidemiological study.

A survey of the United Kingdom detected 282 deaths from abuse of volatile substances during 1971-83. Deaths appeared to have increased in the most recent years, reaching 80 in 1983. Age at death ranged from 11 to 76 years but most deaths (72%) occurred under 20 years. Ninety five per cent of the subjects were male, and in 1983 deaths from volatile substance abuse accounted for 2% of all deaths in males aged 10-19. All areas of the United Kingdom were affected, the rates being highest in Scotland and urban areas. All social classes were affected, though rates were highest in social class V and the armed forces. The volatile substances abused were gas fuels (24%), mainly butane; aerosol sprays (17%); solvents in glues (27%); and other volatile substances, such as cleaning agents (31%). In 51% of cases death was attributed to the direct toxic effects of the substance abused, in 21% to plastic bag asphyxia, in 18% to inhalation of stomach contents, and in 11% to trauma. Deaths associated with the abuse of glues were more likely to be traumatic, but all substances appeared capable of killing directly by their toxic effects, probably by a cardiac mechanism. Only a small proportion of deaths (6%) were due to the abuse of glues among children under 16; hence current attempts to limit access of children to glues will probably have little impact on overall mortality.     

Automated Entire Thrombus Density Measurements for Robust and Comprehensive Thrombus Characterization in Patients with Acute Ischemic Stroke

Background and Purpose

In acute ischemic stroke (AIS) management, CT-based thrombus density has been associated with treatment success. However, currently used thrombus measurements are prone to inter-observer variability and oversimplify the heterogeneous thrombus composition. Our aim was first to introduce an automated method to assess the entire thrombus density and then to compare the measured entire thrombus density with respect to current standard manual measurements.

Materials and Method

In 135 AIS patients, the density distribution of the entire thrombus was determined. Density distributions were described using medians, interquartile ranges (IQR), kurtosis, and skewedness. Differences between the median of entire thrombus measurements and commonly applied manual measurements using 3 regions of interest were determined using linear regression.

Results

Density distributions varied considerably with medians ranging from 20.0 to 62.8 HU and IQRs ranging from 9.3 to 55.8 HU. The average median of the thrombus density distributions (43.5 ± 10.2 HU) was lower than the manual assessment (49.6 ± 8.0 HU) (p<0.05). The difference between manual measurements and median density of entire thrombus decreased with increasing density (r = 0.64; p<0.05), revealing relatively higher manual measurements for low density thrombi such that manual density measurement tend overestimates the real thrombus density.

Conclusions

Automatic measurements of the full thrombus expose a wide variety of thrombi density distribution, which is not grasped with currently used manual measurement. Furthermore, discrimination of low and high density thrombi is improved with the automated method.     

Indirect Evolution of Hybrid Lethality Due to Linkage with Selected Locus in Mimulus guttatus

Most species are superbly and intricately adapted to the environments in which they live. Adaptive evolution by natural selection is the primary force shaping biological diversity. Differences between closely related species in ecologically selected characters such as habitat preference, reproductive timing, courtship behavior, or pollinator attraction may prevent interbreeding in nature, causing reproductive isolation. But does ecological adaptation cause reproductive incompatibilities such as hybrid sterility or lethality? Although several genes causing hybrid incompatibilities have been identified, there is intense debate over whether the genes that contribute to ecological adaptations also cause hybrid incompatibilities. Thirty years ago, a genetic study of local adaptation to copper mine soils in the wildflower Mimulus guttatus identified a locus that appeared to cause copper tolerance and hybrid lethality in crosses to other populations. But do copper tolerance and hybrid lethality have the same molecular genetic basis? Here we show, using high-resolution genome mapping, that copper tolerance and hybrid lethality are not caused by the same gene but are in fact separately controlled by two tightly linked loci. We further show that selection on the copper tolerance locus indirectly caused the hybrid incompatibility allele to go to high frequency in the copper mine population because of hitchhiking. Our results provide a new twist on Darwin''s original supposition that hybrid incompatibilities evolve as an incidental by-product of ordinary adaptation to the environment.     

Zinc tolerance and hyperaccumulation are genetically independent characters

The hyperaccumulation of metals by a rare class of plants is a fascinating and little understood phenomenon. No genetic analysis has been possible since no intraspecific variation is known for this character. Here, we report on crosses between the zinc-hyperaccumulating and -tolerant species Arabidopsis halleri and the non-hyperaccumulating, non-tolerant species Arabidopsis petraea. The F2 segregates for both characters and it appears that the two characters are genetically independent. The data for tolerance are consistent with a single major gene for this character (although the number of genes for hyperaccumulation cannot be determined), and is probably not very large.     

Ecological and genetic correlates of long-term population trends in the park grass experiment

The Park Grass Experiment (PGE) is the longest-observed set of experimental plant communities in existence. Although the gross composition of the vegetation was at equilibrium over the 60-yr period from 1920 to 1979, annual records show that individual species exhibited a range of dynamics. We tested two hypotheses to explain why some species initially increased and why subsequently some of these (the outbreak species) decreased again. The study was designed around eight phylogenetically independent contrasts (PICs), each containing related species with different dynamics. Our first hypothesis was that persistent increasers and outbreakers have higher intrinsic rates of natural increase than control species (species without trends), allowing them to spread when interspecific competition is reduced by drought. This was tested by measuring establishment and seed production of species in field experiments, with and without interspecific competition. Seed production in outbreak species responded more strongly to release from interspecific competition than it did in either of the other groups of species. Our second hypothesis was that outbreak species eventually declined because they lacked the genetic variation necessary to adapt to the novel habitats to which they had initially spread. We tested this by measuring mating systems and genetic diversity in persistent and outbreak species in the PGE. In seven out of seven PICs tested, the outbreak species was more selfing than its persistent relative. There was a significant positive correlation between outcrossing rate and gene diversity. These results support roles for both ecological and genetic traits in long-term dynamics.     

Towards a framework for the evolutionary genomics of Kinetoplastids: what kind of data and how much?

The current status of kinetoplastids phylogeny and evolution is discussed in view of the recent progresses on genomics. Some ideas on a potential framework for the evolutionary genomics of kinetoplastids are presented.