The impact of UV-B and sulphur- or copper-containing solutions in acidic conditions on chlorophyll fluorescence in selected Ramalina species

Ramalina maciformis and Ramalina lacera were exposed to different solutions and UV-B to seek for alterations in the PSII photosynthetic quantum yield (F(v)/F(m)), in response to chemicals and radiation. For R. maciformis, significant alterations of the F(v)/F(m) ratio occurred only in response to different bisulphite solutions. The F(v)/F(m) ratio decreased most in R. maciformis and R. lacera following exposure to 5 and 1 mM bisulphite, respectively. Significant differences in F(v)/F(m) ratios were observed for R. lacera in response to different solutions and light at different wavelengths, this being synergistic. The PSII system was unaffected by simulated acid rain in both lichens. R. maciformis, in particular, may survive limited acid rain exposure owing to high Ca oxalate accumulation. The F(v)/F(m) ratio decreased most in R. lacera following short-term exposures to CuSO(4), suggesting that this species is more sensitive to Cu ions under acidic conditions.     

Characterization of demethylation of methylmercury in cultured astrocytes

Mercury (Hg) is a well-known neurotoxicant but its toxicity depends on the species present. A steady emergence of inorganic Hg in the brain following chronic and accidental exposure to methylmercury (MeHg) has suggested that MeHg can undergo demethylation. The objective of this study is to develop an in vitro model to study factors affecting Hg demethylation in the central nervous system. Astrocytes obtained from neonatal rat pups were cultured for 24h with 1 microM MeHg in the presence of two pro-oxidants, buthionine sulphoximine (BSO) and rotenone. The BSO treatment produced a 21% increase in reactive oxygen species (ROS) content compared to the control (control vs. BSO; 100+/-1.35 vs. 121+/-1.52 relative fluorescence units (RFU)mg(-1) protein, p<0.001) but did not affect total Hg accumulation (control vs. BSO=86.5+/-4.14 ng mg(-1) vs. 95.7+/-9.26 ng mg(-1)). Rotenone increased ROS levels 107% (control vs. rotenone; 100%+/-1.35 vs. 207%+/-6.78RFU mg(-1)protein, p<0.001) and significantly increased the accumulation of total Hg (control vs. rotenone=86.5+/-4.14 ng mg(-1) vs. 124+/-3.80 ng mg(-1), p<0.001). There was no detectable demethylation in the control or BSO treated group, however, the rotenone treatment significantly increased the demethylation (control vs. rotenone=-1.86+/-5.57% vs. 16.3+/-2.68%, p<0.05). For the first time, we have demonstrated in an in vitro primary astrocyte culture model that MeHg can be converted to inorganic Hg and demethylation increases with oxidative stress. Our results provide a useful model to study demethylation of Hg in astrocytes and to explore potential ways to protect against Hg toxicity.     

Hepatopancreatic endosymbionts in coastal isopods (Crustacea: Isopoda), and their contribution to digestion

Three isopod species (Crustacea: Isopoda), commonly found in the intertidal and supratidal zones of the North American Pacific coast, were studied with respect to symbiotic microbiota in their midgut glands (hepatopancreas). Ligia pallasii (Oniscidea: Ligiidae) contained high numbers of microbial symbionts in its hepatopancreatic caeca. Numbers of endosymbionts were strongly reduced by ingestion of antibiotics. By contrast, the hepatopancreas of Idotea wosnesenskii (Valvifera: Idoteidae) and Gnorimosphaeroma oregonense (Sphaeromatidea: Sphaeromatidae) did not contain any microbiota. Results of feeding experiments suggest that microbial endosymbionts contribute to digestive processes in L. pallasii, the most terrestrial of the three isopods that we studied. The acquisition of digestion-enhancing endosymbionts may have been an important evolutionary step allowing isopods to colonize terrestrial habitats where relatively indigestible leaf litter is the primary food source. By contrast, the ability to digest phenolic compounds was most developed in one of the more marine species, suggesting that this trait may have evolved independently in isopod species that consume a phenolic-rich diet, whether in marine habitats or on land. Received: 28 August 2000 / Accepted: 8 December 2000     

Regulation of ovary activation in worker honey-bees (Apis mellifera): larval signal production and adult response thresholds differ between anarchistic and wild-type bees

One-day-old anarchistic (selected for successful worker reproduction) and wild-type honey-bee workers were introduced into queenright colonies of honey-bees of two treatments. In treatment 1, all eggs and larvae were offspring of queens from an anarchistic line. In treatment 2, all eggs and larvae were offspring of wild-type queens. In both treatments, adult workers were wild type. This experimental arrangement was used to test the importance of larval genotype on ovary activation in young adult workers. After 12 days, the introduced bees were dissected to determine the frequency of ovary activation. In those colonies provided with wild-type brood, 0% of introduced wild-type bees and 16% of anarchistic bees had activated ovaries. In those colonies provided with anarchistic brood, 13% of introduced wild-type bees and 41% of anarchistic bees had activated ovaries. These results strongly support the hypothesis that selection for high levels of worker reproduction in anarchistic stocks has reduced the amount or composition of brood pheromones produced by larvae that normally signal workers to refrain from reproduction. They also suggest that anarchistic workers have a higher threshold for these signals than wild-type bees.     

Predicting the Risk of Extinction through Hybridization

Abstract: Natural hybridization threatens a substantial number of plant and animal species with extinction, but extinction risk has been difficult to evaluate in the absence of a quantitative assessment of risk factors. We investigated a number of ecological parameters likely to affect extinction risk, through an individual-based model simulating the life cycle of two hybridizing annual plant species. All parameters tested, ranging from population size to variance in pollen-tube growth rates, affected extinction risk. The sensitivity of each parameter varied dramatically across parameter sets, but, overall, the competitive ability, initial frequency, and selfing rate of the native taxon had the strongest effect on extinction. In addition, prezygotic reproductive barriers had a stronger influence on extinction rates than did postzygotic barriers. A stable hybrid zone was possible only when habitat differentiation was included in the model. When there was no habitat differentiation, either one of the parental species or the hybrids eventually displaced the other two taxa. The simulations demonstrated that hybridization is perhaps the most rapidly acting genetic threat to endangered species, with extinction often taking place in less than five generations. The simulation model was also applied to naturally hybridizing species pairs for which considerable genetic and ecological information is available. The predictions from these "worked examples" are in close agreement with observed outcomes and further suggest that an endemic cordgrass species is threatened by hybridization. These simulations provide guidance concerning the kinds of data required to evaluate extinction risk and possible conservation strategies.     

Closing the material cycle of biomass-derived fly ashes: a regional case study of natural ageing in Finland

Journal of Material Cycles and Waste Management - The amount of biomass-derived ashes is expected to rise in the EU due to targets to increase the use of renewable energy resources. To promote the...     

Fir decline and mortality in the southern Siberian Mountains

Regional Environmental Change - Increased dieback and mortality of “dark needle conifer” (DNC) stands (composed of fir (Abies sibirica), Siberian pine (Pinus sibirica) and spruce (Picea...     

Stable carbon isotope ratio in xylotrophic fungi and their substrates

Data on the ratio of stable carbon isotopes in xylotrophic fungi and their xylic substrates are presented for the first time. It is shown that coniferous substrates are more enriched in the heavy carbon isotope, compared to deciduous substrates. In both cases, however, their carbon isotope composition is characterized by low variability and does not correlate with the species or physiological type of decomposer fungus but shows a statistically significant correlation with the degree of wood mineralization. The ratio of stable carbon isotopes in the fungi depends on that in their substrates but is shifted in favor of the heavier isotope. This trophic shift lacks species specificity, is equally manifested in decomposers of deciduous and coniferous substrates, remains unchanged along the latitudinal climatic gradient, and is positively correlated with the carbon isotope composition of substrates, in the absence of correlation with the degree of their mineralization.     

Seasonal ecophysiology of an endangered coastal species,the yellow-horned poppy (Glaucium flavum Crantz)

Glaucium flavum Crantz. is a short-lived perennial herb distributed in coastal zones from the Black Sea to southern, western and north-western Europe. Despite its diminishing area of distribution and potential pharmacological value, little is known about the ecophysiological features of this coastal species. We investigated the photosynthetic performance of G. flavum by measuring gas exchange, chlorophyll fluorescence, photosynthetic pigment concentration and leaf water content over the space of a year in a coastal habitat of SW Spain. We also measured the variation in total concentrations of nitrogen, phosphorus, sulphur, potassium, calcium and magnesium, in the leaves and soil, throughout the study period. G. flavum showed a high resistance to summer drought conditions which appeared to be due to the high degree of stomatal control. The potential photochemical efficiency of photosystem II showed minimum values during the winter, indicating that low temperatures can produce negative effects within the photosynthetic apparatus. However, the marked decline in net photosynthesis during the winter seems to be mainly related to a loss of metabolic activity. Although leaf nutrient concentrations were, in general, within the normal ranges, phosphorus availability seems to be limited by the high calcium concentrations detected in the soil of the study site. Our study points out the efficiency of the different physiological adaptations of this rare and endangered coastal species in coping with the strong seasonal variability of the Mediterranean climate.