Are environmental electromagnetic fields genotoxic?

Long-term exposure to extremely-low-frequency electromagnetic fields (ELF EMFs) greater than 0.4 microT has been linked, by epidemiological studies, to a small elevated risk of childhood leukaemia. Laboratory-based experiments have been claimed to show that ELF EMFs induce a variety of biological responses, although these claims are controversial. Recent experiments by Ivancsits et al. [Mutat. Res. 519 (2002) 1; Int. Arch. Occup. Environ. Health 76 (2003) 431; Mech. Age. Dev. 124 (2003) 847; H.W. Rüdiger, S. Ivancsits, E. Diem, O. Jahn, Genotoxic effects of ELF-EMF on human cells in vitro, Bioelectromagnetics Society 25th Annual Meeting, Maui, USA, 2003] suggest that ELF EMFs are genotoxic, on the basis of observations that intermittent exposures induce single-strand breaks (SSB) and double-strand DNA breaks (DSB) in the DNA of cultured human fibroblasts. The implications of these findings are discussed.     

How do environmental stresses accelerate photoinhibition?

Environmental stress enhances the extent of photoinhibition, a process that is determined by the balance between the rate of photodamage to photosystem II (PSII) and the rate of its repair. Recent investigations suggest that exposure to environmental stresses, such as salt, cold, moderate heat and oxidative stress, do not affect photodamage but inhibit the repair of PSII through suppression of the synthesis of PSII proteins. In particular, production of D1 protein is downregulated at the translation step by the direct inactivation of the translation machinery and/or by primarily interrupting the fixation of CO2. The latter results in the creation of reactive oxygen species (ROS), which in turn block the synthesis of PSII proteins in chloroplasts.     

How to value biodiversity in environmental management?

Biodiversity is globally recognised as a cornerstone of healthy ecosystems, and biodiversity conservation is increasingly becoming one of the important aims of environmental management. Evaluating the trade-offs of alternative management strategies requires quantitative estimates of the costs and benefits of their outcomes, including the value of biodiversity lost or preserved. This paper takes a decision-analytic standpoint, and reviews and discusses the alternative aspects of biodiversity valuation by dividing them into three categories: socio-cultural, economic, and ecological indicator approaches. We discuss the interplay between these three perspectives and suggest integrating them into an ecosystem-based management (EBM) framework, which permits us to acknowledge ecological systems as a rich mixture of interactive elements along with their social and economic aspects. In this holistic framework, socio-cultural preferences can serve as a tool to identify the ecosystem services most relevant to society, whereas monetary valuation offers more globally comparative and understandable values. Biodiversity indicators provide clear quantitative measures and information about the role of biodiversity in the functioning and health of ecosystems. In the multi-objective EBM approach proposed in the paper, biodiversity indicators serve to define threshold values (i.e., the minimum level required to maintain a healthy environment). An appropriate set of decision-making criteria and the best method for conducting the decision analysis depend on the context and the management problem in question. Therefore, we propose a sequence of steps to follow when quantitatively evaluating environmental management against biodiversity.     

When does environmental variation most influence species coexistence?

The ability of environmental variation to affect species coexistence is much studied, yet environmental variation is not always important. I present an approximate calculation for the long-run growth rate of a species in the presence of spatially and temporally correlated environmental variation. I then perform a factorial numerical experiment, varying the mean seed dispersal distances, competition radii, and overwinter seed survival probabilities for two competing species for an array of variational regimes, noting the effects on their long-run growth rates. I find, first, that purely spatial variation has a greater capacity for influence than variation with a temporal component. Second, spatiotemporal variation can promote coexistence as strongly as purely temporal variation or more so, given the right species traits. Third, if the environmental variation has a spatial component, traits which enable species to become spatially segregated promote coexistence most strongly. That is, it is the possibility of spatial segregation which gives spatial variation its large potential to promote coexistence.

Reactive oxygen species: the unavoidable environmental insult?

Reactive oxygen species (ROS) are generated by a variety of sources from the environment (e.g., photo-oxidations and emissions) and normal cellular functions (e.g., mitochondrial metabolism and neutrophil activation). ROS include free radicals (e.g., superoxide and hydroxyl radicals), nonradical oxygen species (e.g., hydrogen peroxide and peroxynitrite) and reactive lipids and carbohydrates (e. g., ketoaldehydes, hydroxynonenal). Oxidative damage to DNA can occur by many routes including the oxidative modification of the nucleotide bases, sugars, or by forming crosslinks. Such modifications can lead to mutations, pathologies, cellular aging and death. Oxidation of proteins appears to play a causative role in many chronic diseases of aging including cataractogenesis, rheumatoid arthritis, and various neurodegenerative diseases including Alzheimer's Disease (AD). Our goal is to elucidate the mechanism(s) by which oxidative modification results in the disease. These studies have shown that (a) cells from old individuals are more susceptible to oxidative damage than cells from young donors; (b) oxidative protein modification is not random; (c) some of the damage can be prevented by antioxidants, but there is an age-dependent difference; and (d) an age-related impairment of recognition and destruction of modified proteins exists. It is believed that mechanistic insight into oxidative damage will allow prevention or intervention such that these insults are not inevitable. Our studies are also designed to identify the proteins which are most susceptible to ROS damage and to use these as potential biomarkers for the early diagnosis of diseases such as AD. For example, separation of proteins from cells or tissues on one- and two-dimensional gels followed by staining for both total protein and specifically oxidized residues (e.g., nitrotyrosine) may allow identification of biomarkers for AD.     

Marine biodiversity�Cecosystem functions under uncertain environmental futures

Anthropogenic activity is currently leading to dramatic transformations of ecosystems and losses of biodiversity. The recognition that these ecosystems provide services that are essential for human well-being has led to a major interest in the forms of the biodiversity–ecosystem functioning relationship. However, there is a lack of studies examining the impact of climate change on these relationships and it remains unclear how multiple climatic drivers may affect levels of ecosystem functioning. Here, we examine the roles of two important climate change variables, temperature and concentration of atmospheric carbon dioxide, on the relationship between invertebrate species richness and nutrient release in a model benthic estuarine system. We found a positive relationship between invertebrate species richness and the levels of release of NH₄-N into the water column, but no effect of species richness on the release of PO₄-P. Higher temperatures and greater concentrations of atmospheric carbon dioxide had a negative impact on nutrient release. Importantly, we found significant interactions between the climate variables, indicating that reliably predicting the effects of future climate change will not be straightforward as multiple drivers are unlikely to have purely additive effects, resulting in increased levels of uncertainty.     

Microfragmentation concept explains non-positive environmental heterogeneity–diversity relationships

Although recent studies have revealed that the relationship between diversity and environmental heterogeneity is not always positive, as classical niche theory predicts, scientists have had difficulty interpreting these results from an ecological perspective. We propose a new concept—microfragmentation—to explain how small-scale heterogeneity can have neutral or even negative effect on species diversity. We define microfragmentation as a community level process of splitting habitat into a more heterogeneous environment that can have non-positive effects on the diversity through habitat loss and subsequent isolation. We provide support for the microfragmentation concept with results from spatially explicit heterogeneity–diversity model simulations, in which varying sets of species (with different ratios of specialist and generalist species) were modeled at different levels of configurational heterogeneity (meaning that only the habitat structure was changed, not its composition). Our results indicate that environmental heterogeneity can affect community diversity in the same way as fragmentation at the landscape level. Although generalist species might not be seriously affected by microfragmentation, the persistence of specialist species can be seriously disturbed by small-scale patchiness. The microfragmentation concept provides new insight into community level diversity dynamics and can influence conservation and management strategies.     

Is sexual selection beneficial during adaptation to environmental change?

The role of sexual selection in adaptation is disputed. A balance between sexual and viability selection can be achieved in stable environments, but environmental perturbations could change the costs and benefits arising from sexual selection and influence the rate of adaptation. Here we synthesise theoretical and empirical work on the role of sexual selection in adaptation to changed conditions. Contrasting results have been gained, but the majority of studies suggest that sexual selection has no significant effect or a negative effect on the rate of adaptation. However, once sexually selected traits start to evolve, sexual selection can accelerate adaptation. The role of sexual selection in extinction appears to be minor, but the results could be skewed.     

Bacterial metabolism of environmental arsenic—mechanisms and biotechnological applications

Arsenic causes threats for environmental and human health in numerous places around the world mainly due to its carcinogenic potential at low doses. Removing arsenic from contaminated sites is hampered by the occurrence of several oxidation states with different physicochemical properties. The actual state of arsenic strongly depends on its environment whereby microorganisms play important roles in its geochemical cycle. Due to its toxicity, nearly all organisms possess metabolic mechanisms to resist its hazardous effects, mainly by active extrusion, but also by extracellular precipitation, chelation, and intracellular sequestration. Some microbes are even able to actively use various arsenic compounds in their metabolism, either as an electron donor or as a terminal electron acceptor for anaerobic respiration. Some microorganisms can also methylate inorganic arsenic, probably as a resistance mechanism, or demethylate organic arsenicals. Bioavailability of arsenic in water and sediments is strongly influenced by such microbial activities. Therefore, understanding microbial reactions to arsenic is of importance for the development of technologies for improved bioremediation of arsenic-contaminated waters and environments. This review gives an overview of the current knowledge on bacterial interactions with arsenic and on biotechnologies for its detoxification and removal.     

How to detect Toxoplasma gondii oocysts in environmental samples?

Detection of Toxoplasma gondii oocysts in environmental samples is a great challenge for researchers as this coccidian parasite can be responsible for severe infections in humans and in animals via ingestion of a single oocyst from contaminated water, soil, fruits or vegetables. Despite field investigations, oocysts have been rarely recovered from the environment due to the lack of sensitive methods. Immunomagnetic separation, fluorescence-activated cell sorting, and polymerase chain reaction have recently shown promising use in detection of protozoa from complex matrices. Such procedures could be applied to T. gondii detection, if studies on the antigenic and biochemical composition of the oocyst wall are completed. Using such methods, it will be possible to assess the occurrence, prevalence, viability and virulence of T. gondii oocysts in environmental matrices and specify sources of human and animal contamination.     

Can environmental fluctuation prevent competitive exclusion in sympatric flycatchers?

Ecology has been characterized by a central controversy for decades: namely, whether the distribution and abundance of organisms are determined by species interactions, such as competitive exclusion, or by environmental conditions. In part, this is because competitive exclusion has not been convincingly demonstrated in open, natural systems. In addition, traditional theoretical models cannot predict the outcome of competitive interactions in the presence of environmental variability. In this paper we document the limiting influence of strong interspecific competition on population dynamics and nestling mortality in a mixed population of pied flycatchers (Ficedula hypoleuca) and collared flycatchers (F. albicollis in a narrow zone of sympatry. Whereas the former species was limited mainly by interspecific competition, the latter species was limited by the concerted influences of intraspecific competition and climate. The analysis suggests a march towards competitive exclusion of the pied flycatcher during warm periods. However, competitive exclusion is apparently prohibited on a local scale because intraspecific competition among individual collared flycatchers intensifies when they are forced to cope with severe environmental conditions, promoting the temporary and local presence of pied flycatchers.     

Genome instability and epigenetic modification--heritable responses to environmental stress?

As sessile organisms, plants need to continuously adjust their responses to external stimuli to cope with changing growth conditions. Since the seed dispersal range is often rather limited, exposure of progeny to the growth conditions of parents is very probable. The plasticity of plant phenotypes cannot be simply explained by genetic changes such as point mutations, deletions, insertions and gross chromosomal rearrangements. Since many environmental stresses persist for only one or several plant generations, other mechanisms of adaptation must exist. The heritability of reversible epigenetic modifications that regulate gene expression without changing DNA sequence makes them an attractive alternative mechanism. In this review, we discuss recent advances in understanding how changes in genome stability and epigenetically mediated changes in gene expression could contribute to plant adaptation. We provide examples of environmentally induced transgenerational epigenetic effects that include the appearance of new phenotypes in successive generations of stressed plants. We also describe several cases in which exposure to stress leads to nonrandom heritable but reversible changes in stress tolerance in the progeny of stressed plants.     

Are ruminal bacteria protected against environmental stress by plant antioxidants?

AIMS: To investigate the activity response of the antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSHPx) of the rumen bacterium Streptococcus bovis following exposure to mercury(II) chloride (HgCl(2) in the presence of plant antioxidants. METHODS AND RESULTS: Streptococcus bovis was grown with 0 or 5 microg ml(-1) of HgCl(2) alone or together with antioxidant substances (AOS): seleno-l-methionine (Se), alpha-tocopherol (alpha toc), beta-carotene (beta car), melatonin (mel). The activities of SOD and GHPx were estimated in supernatants of disrupted bacterial cells. A significant decrease in the Strep. bovis SOD activity in the presence of HgCl(2) and tested AOS, except mel, was observed. The GSHPx activity of Strep. bovis was under the same cultivation conditions nonsignificantly changed and a significant decrease in the GSHPx activity was recorded only in the presence of beta car. CONCLUSIONS: The positive effect of Se, alpha toc and beta car on the elimination of environmental stress, evoked by mercury, in ruminal bacterium Strep. bovis in vitro was documented. SIGNIFICANCE AND IMPACT OF THE STUDY: The potential role of plant antioxidants in elimination of the environmental stress of ruminal bacteria evoked by heavy metals is discussed.     

Masting in a temperate tree: Evidence for environmental prediction?

Many plant species produce large fruit crops in some years and then produce few or no fruits in others. Synchronous, inter‐annual variation in plant reproduction is known as ‘masting’ and its adaptive significance has yet to be fully resolved. For 8 consecutive years, I quantified every fruit produced by 22 females of a New Zealand tree species (Dysoxylum spectabile), which has an unusual habit of taking a full calendar year to mature fruits after flowering. Fruit production varied strongly among years and was tightly synchronized among trees. Annual variability in fruit production declined with total reproductive output, indicating trees with lower fecundity exhibited a stronger tendency to mast. Although unrelated to temperature, annual fruit production was positively related to precipitation during annual periods of fruit development, and negatively related to fruit production in the previous year. Seedlings had higher rates of survivorship in a wet, high‐seed year than in a dry, low‐seed year, suggesting that seedlings might be drought sensitive. Therefore, D. spectabile produced large fruit crops during periods of high rainfall prior to fruit maturation, which may enhance survivorship of drought‐intolerant seeds. Results were inconsistent with several hypotheses that are widely believed to be the most likely explanations for masting. Instead, results were consistent with the environmental prediction hypothesis, suggesting that this hypothesis may be more important than previously appreciated.