Trees as environmental sentinels

Trees are reliable indicators of the long-term effects of atmospheric pollution. As the botanical big game of the planet they are also standing guard and may be providing a warning signal about our own future.     

Migrating shorebirds as integrative sentinels of global environmental change

Many shorebirds travel over large sections of the globe during the course of their annual cycle and use habitats in many different biomes and climate zones. Increasing knowledge of the factors driving variations in shorebird numbers, phenotype and behaviour may allow shorebirds to serve as 'integrative sentinels' of global environmental change. On the basis of numbers, timing of migration, plumage status and body mass, shorebirds could indicate whether ecological and climate systems are generally intact and stable at hemispheric scales, or whether parts of these systems might be changing. To develop this concept, we briefly review the worldwide shorebird migration systems before examining how local weather and global climatic features affect several performance measures of long-distance migrants. What do variations in numbers, phenotype and behaviour tell us about the dependence of shorebirds on weather and climate? How does data on migrating shorebirds integrate global environmental information? Documenting the dependencies between the population processes of shorebirds and global environmental features may be an important step towards assessing the likely effects of projected climate change. In the meantime we can develop the use of aspects of shorebird life histories on large spatial and temporal scales to assay global environmental change.     

Wild mink (Neovison vison) as sentinels in environmental monitoring

Superficial inguinal lymph nodes from 72 wild boars examined in a previous immunohistochemical (IHC) study on porcine circovirus type 2 (PCV2) were selected for a PCV2 polymerase chain reaction (PCR) analysis. Four of these lymph nodes were PCV2-IHC strongly positive with PMWS histological lesions (outcome 1), 6 weak to mild PCV2-IHC positive without PMWS histological lesions (outcome 2) and 62 PCV2-IHC negative. Considering IHC the gold standard for diagnosis, the aims of the study were to evaluate the suitability of the PCV2-DNA extraction from formalin-fixed and paraffin-embedded (FFPE) tissue and the sensitivity and specificity of PCR under two IHC interpretations criteria: (A) the sample was considered positive if the result was outcome 1; (B) the sample was considered positive if the result was outcome 1 or 2. Under (A) criteria, sensitivity and specificity of PCR were 100% and 89.7%, respectively; the Cohen's Kappa coefficient was 0.49. Under (B) criteria, sensitivity and specificity of PCR were 80.0% and 95.2%, respectively; the Cohen's Kappa coefficient was 0.72. The high Cohen's Kappa coefficient under the (B) interpretative criteria indicates good agreement between the two methods. In conclusion, 1) DNA extracted from FFPE specimens of wild boar is suitable for PCR and further represents a screening test for PCV2/PCVD (PCV2 Diseases) investigations in wild boar as well; 2) routine histological sampling can also be useful for PCV2 virological studies in wild boar.     

Dendritic cells: sentinels against pathogens

Dendritic cells (DCs) are the most potent antigen-presenting cells, and are regarded as "natural adjuvants" for the induction of primary T or T-dependent immunity. DCs in the peripheral sites capture and process antigens. Encounter of exogenous or endogenous stimuli mature the function of DCs, and they thus acquire T-cell stimulatory capacity and distinct chemotactic behavior which enables them to migrate to lymphoid tissue. In the secondary lymphoid organs, they present antigens to T- and B-cells and stimulate their proliferation. Dendritic cells are also involved in tolerance induction, in particular, to self antigens. DCs also play a key role in the transmission of many pathogens, and therefore may become targets for designing new therapies. DCs have been manipulated in vitro and in vivo for cancer immunotherapy. In this article, we provide a concise overview of DC biology and its current and future role in clinical settings.     

Endocrine regulation of the reproduction in crustaceans: Identification of potential targets for toxicants and environmental contaminants

Progress in ecotoxicological research documents that crustaceans are highly vulnerable to diverse chemicals and toxicants in the environment. In particular, pollutants affecting endocrine homeostasis in crustaceans (i.e., endocrine disruptors) are intensively studied, and serious reproductive disorders have been documented. In this review, current knowledge about the endocrine regulation of the crustacean reproduction is put together with the published ecotoxicological data with an attempt to summarize the potential of xenobiotics to affect crustacean reproduction. Following gaps and trends were identified: (1) Studies are required in the field of neurohormone (serotonin and dopamine) regulation of the reproduction and possible modulations by environmental toxicants such as antidepressant drugs. (2) Molting-related parameters (regulated by ecdysteroid hormones) are closely coordinated with the development and reproduction cycles in crustaceans (cross-links with methyl farnesoate signalling), and their susceptibility to toxicants should be studied. (3) Other biochemical targets for xenobiotics were recently discovered in crustaceans and these should be explored by further ecotoxicological studies (e.g., new information about ecdysteroid receptor molecular biology). (4) Some sex steroid hormones known from vertebrates (testosterone, progesterone) have been reported in crustaceans but knowledge about their targets (crustacean steroid receptors) and signalling is still limited. (5) Determination of the sex in developing juveniles (affecting the sex ratio in population) is a sensitive parameter to various xenobiotics (including endocrine disruptors) but its modulation by general environmental stress and non-specific toxicity should be further studied.     

Gut nociceptors: sentinels promoting host defense

Gut-innervating nociceptive neurons detect noxious mechanical and chemical stimuli within our gut, constituting the start of the'gut pain'pathway.In a recent pa...     

Inter-individual differences in the metabolism of environmental toxicants: cytochrome P450 1A2 as a prototype.

Cytochrome P450 (P450) 1A2 provides an interesting paradigm for inter-individual differences in the metabolism of pro-carcinogens. The enzyme is known to vary 40-fold among individuals and may contribute to cancers caused by heterocyclic amines and other chemicals. Rat and human P450 1A2 are known to be 75% identical and were compared for several catalytic activities. The human enzyme was an order of magnitude more efficient in the N-hydroxylation of two heterocyclic amines. Further, the levels of P450 1A2 expressed in human livers show a 40-fold variation, with some as high as 0.25 nmol P450 1A2 per milligram microsomal protein. Some human liver samples are more active (than those isolated from polychlorinated biphenyl-treated rats) in the activation of heterocyclic amines. A bacterial genotoxicity assay has been developed in which human P450 1A2 and NADPH-P450 reductase are expressed within Escherichia coli and bacterial mutants can be assayed using reversion to lac prototrophy. A random mutagenesis strategy for human P450 1A2 has been developed and used to examine the changes in catalytic activity seen with many single-amino acid substitutions. These results may be of relevance in consideration of genetic polymorphisms. Further, the findings pose a challenge to molecular epidemiology effort in that results with one substrate do not necessarily predict those for others. Some dinitropyrenes are P450 1A2 substrates but others are not. 6-Nitrochrysene can be activated by human P450 1A2 but the (mono) nitropyrenes examined were not; these were oxidized by P450 3A4 instead.     

Transition-state regulators: sentinels of Bacillus subtilis post-exponential gene expression

When Bacillus subtilis encounters a nutrient-depleted environment, it expresses a wide variety of genes that encode functions in alternative pathways of metabolism and energy production. Expression of these genes first occurs during the transition from active growth into stationary phase and is controlled by a class of proteins termed transition-state regulators. In several instances, a given gene is redundantly controlled by two or more of these regulators and many of these regulators control genes in numerous different pathways. The AbrB, Hpr and Sin proteins are the best-studied examples of these regulatory molecules. Their role is to prevent inappropriate and possibly detrimental functions from being expressed during exponential growth when they are not needed. They serve as elements integrating sporulation with ancillary stationary-phase phenomena and appear to participate in the timing of early sporulation events and in fine-tuning the magnitude of gene expression in response to specific environmental conditions.     

State-dependent sentinels: an experimental study in the Arabian babbler

Natural patterns of cooperative sentinel behaviour in Arabian babblers, Turdoides squamiceps, have proven consistent with state-dependent models of individually selfish anti-predator strategies. Here we demonstrate experimentally that sentinel effort within groups is determined simply by individual state. The two highest-ranking males in eight groups were separately fed a supplement of mealworms, each for one day at a time. Control days before and after each treatment confirmed that no carry-over effects occurred, and that most normal sentinel activity was carried out by alpha males, then beta males and then by the rest of the group. When supplemented, both alpha and beta males exhibited similar marked increases in sentinel activity, relative to control days. Unsupplemented males and the rest of the group incompletely compensated for these increases with reductions in sentinel effort. Differences in individual body mass within groups reflected natural and experimental variation in sentinel effort. Alpha and beta males weighed more than other group members, and gained mass only when supplementally fed. There was no evidence either for competitive sentinel behaviour, nor for any increased interference between males during the supplementation treatments. These results therefore provide strong evidence in support of the state-dependent approach to cooperative sentinel behaviour.     

Mutualism among safe, selfish sentinels: a dynamic game

Sentinels are group members that watch from prominent positions. Sentinel interchanges often appear orderly, and groups with sentinels rarely have zero or many sentinels. A dynamic game was constructed to examine if these observations about sentinels could be based on selfish actions by individual group members. In this game, each group member chose to forage or be a sentinel based on its own energetic state and the actions of others. Sentinels received a selfish antipredator benefit if their ability to detect approaching predators more than compensated for their increased exposure to undetected predators. Provided sentinels were relatively safe and that detection information spread to other group members when sentinels detected predators, sentinels appeared highly coordinated for all combinations of parameters. This apparent coordination was based on mutualism because each individual gained by being a sentinel when other group members were not (and foraging when other group members were being sentinels). The model was very robust, but exact level of sentinel behavior varied somewhat with changes in foraging and predation parameters. This model could best be tested by testing its assumptions about sentinel safety, foraging-predation trade-offs, and information transfer in groups.     

Small mammals as sentinels of antimicrobial-resistant staphylococci

A total of 39 coagulase-negative staphylococci and seven Staphylococcus aureus strains were isolated from small mammal feces, i.e., the striped field mouse (Apodemus agrarius) and the yellow-necked mouse (A. flavicollis) in two sampling areas, deciduous forest and karst plains. MALDI-TOF analysis revealed five species of coagulase-negative staphylococci: S. sciuri, S. hominis, S. warneri, S. haemolyticus, and S. xylosus. All strains were susceptible to tetracycline, linezolid, vancomycin, and teicoplanin. Three MRSA strains with the mecA gene were detected. The beta-lactamase gene blaZ was detected in ampicillin-resistant staphylococci and in the high-level resistant strains (oxacillin over 2 mg/L) mecA gene. The mecC gene was not detected by PCR. Erythromycin-resistant staphylococci harbored the ermC gene and/or the efflux gene msrA. There were no detectable dfr genes in trimethoprim-resistant staphylococci and the rifampicin-resistant strains were without mutation in the rpoB gene. In summary, wild small mammals may serve as sentinels of mecA-positive S. aureus with erythromycin resistance genes ermC and efflux msrA. Small mammals appear to be useful indicators of antibiotic resistance.     

Mechanisms involved in the neurotoxic effects of environmental toxicants such as polychlorinated biphenyls and brominated flame retardants

Many toxic substances have been distributed to the environment, some of which have properties that promote accumulation and biomagnification in living organisms. Approximately 1.2 million metric tons of polychlorinated biphenyls (PCBs) have been produced and about 30% have been discharged to the environment. Approximately 200 000 metric tons of brominated flame retardants (BFRs) are produced annually, of which considerable amounts have been spread globally, even to the Polar Regions. Behavioral testing of animals has shown that these compounds may affect learning, memory and fine motor functions. Animals are most sensitive during early development. Several epidemiological studies have shown that PCBs and BFRs may be responsible for similar effects in humans. Of especially concern are possible effects of PCBs and BFRs in mixtures containing the highly neurotoxic methyl mercury. The compounds affect several targets in the nervous system that seem to be interconnected, and may be responsible for the observed behavioral deficits. It was shown early that PCBs affect dopamine and serotonin levels in the brain. Later studies showed that transport mechanisms of these neurotransmitters appear to be particularly sensitive to PCBs. Furthermore, PCBs affect intracellular calcium levels and induce formation of reactive oxygen species both in vivo and in vitro, and reduce cell viability in vitro. Neuroendocrine functions, particularly the thyroid hormone system, are also sensitive to disruption by PCBs and BFRs. Their metabolites, such as hydroxy‐metabolites, appear to be particularly potent. We conclude that PCBs are particularly toxic during early development and that the toxic effects are a combination of several factors, including disturbance of calcium homeostasis, oxidative stress, and influence on neurotransmitter transport. Monoaminergic cells appear to be particularly vulnerable.     

Physiological costs of combating chemical toxicants: Ecological implications

• 1.1. Evidence is presented that combating the poisoning effects of toxic chemicals is metabotically costly.
• 2.2. This has implications for relating physiological stress responses observed at the level of individual organisms to population effects, and needs to be incorporated explicitly into models making this link.
• 3.3. The cost hypothesis also has implication for the evolution of stress resistance either as a fixed or facultative (inducible) response. Optimization models incorporating these ideas are reviewed and discussed.

     

A novel group of ovarian toxicants: the psoralens

The psoralens are naturally occurring metabolites found in many crop plants; synthetic forms of 5-methoxypsoralen (bergapten) and 8-methoxypsoralen (xanthotoxin) are widely used in skin photochemotherapy. Our previous research documented that dietary bergapten and xanthotoxin reduced birthrates in female rats when males and females were exposed to these chemicals. The present study was designed to determine the cause of this reduced birthrate and whether this resulted from direct impact on the females. The study demonstrates that bergapten and xanthotoxin administered, either alone or in combination to female rats (mated to undosed males), significantly reduced the number of implantation sites, pups, and corpora lutea in dosed females compared with control animals. Additionally, full uterine weight and empty uterine weight were significantly reduced. These compounds also significantly reduced circulating estrogen levels in a dose-dependent manner. Interestingly, the psoralens significantly induced mRNAs of liver enzymes typically induced by polycyclic aromatic hydrocarbons, CYP1A1 and UGT1A6; the higher the dose, the greater the induction. UGT 2B1 mRNA, typically induced by phenobarbital-like compounds, was not significantly affected. Thus, enhanced oxidative metabolism and conjugation of estrogens in psoralen-treated animals may provide a partial explanation for the effects observed. These findings are also consistent with psoralen-induced reduction in ovarian follicular function and ovulation.