Diurnal variations in the auto- and heterotrophic activity of cyanobacterial phycospheres (Gloeotrichia echinulata) and the identity of attached bacteria

1. We assessed the role of cyanobacterial–bacterial consortia (Gloeotrichia echinulata phycospheres) for net changes in inorganic carbon, primary production (PP) and secondary production in Lake Erken (Sweden). 2. At the time of sampling, large colonies of G. echinulata formed a massive bloom with abundances ranging from 102 colonies L^?1 in the pelagic zone to 5000 colonies L^?1 in shallow bays. These colonies and their surrounding phycospheres contributed between 17 and 92% of total PP, and phycosphere‐associated bacteria contributed between 8.5 and 82% of total bacterial secondary production. PP followed a diurnal cycle, whereas bacterial production showed no such pattern. Over a 24 h period, carbon dioxide measurements showed that the phycospheres were net autotrophic in the top layer of the water column, whereas they were net heterotrophic below 2 m depth. 3. Sequencing and phylogenetic analysis of 16S rRNA genes of attached bacteria revealed a diverse bacterial community that included populations affiliated with Proteobacteria, Bacteriodetes, Acidobacteria, Fusobacteria, Firmicutes, Verrucomicrobia, and other Cyanobacteria. 4. Compared with their planktonic counterparts, bacteria associated with cyanobacterial phycospheres had lower affinity for arginine, used as a model compound to assess uptake of organic compounds. 5. Extrapolation of our data to the water column of lake Erken suggests that microorganisms that were not associated with cyanobacteria dominated CO₂ production at the ecosystem scale during our experiments, as CO₂ fixation balanced CO₂ production in the cyanobacterial phycospheres.     

Increased growth and recruitment of piscivorous perch, Perca fluviatilis, during a transient phase of expanding submerged vegetation in a shallow lake

1. In this study, we examine how a 7‐year period of expanding submerged stonewort (Chara spp.) vegetation during a shift from turbid to clear water in a shallow lake influenced individual growth and population size structure of perch (Perca fluviatilis). We expected that a shift from phytoplankton to macrophyte dominance and clear water would improve feeding conditions for perch during a critical benthivorous ontogenetic stage, and enhance the recruitment of piscivorous perch. 2. Growth analysis based on opercula showed that growth during the second year of life was significantly higher in years with abundant vegetation than in years with turbid water and sparse vegetation. Growth was not affected during the first, third and fourth year of life. Stable isotope analyses on opercula from 2‐year‐old perch showed that the increase in growth coincided with a change in carbon source in the diet. Stable nitrogen ratio did not change, indicating that the increased growth was not an effect of any change in trophic position. 3. Following the expansion of submerged vegetation, perch size range and abundance of piscivorous perch increased in central, unvegetated areas of the lake. In stands of stoneworts, however, mainly benthivorous perch were caught, and size range did not change with time. 4. Our findings provide empirical support for the notion that establishment of submerged vegetation may lead to increased recruitment of piscivorous perch, because of improved competitive conditions for perch during the benthivorous stage. This is likely to constitute a benthic‐pelagic feedback coupling, in which submerged vegetation and clear water promote the recruitment of piscivorous perch, which, in turn, may increase water clarity through top‐down effects in the pelagic.     

Strong impact of wintering waterbirds on zebra mussel (Dreissena polymorpha) populations at Lake Constance, Germany

1. Since zebra mussel invaded Lake Constance in the 1960s the number of wintering waterbirds increased fourfold. We studied the impact of predation by waterbirds (tufted duck Aythya fuligula, pochard Aythya ferina and coot Fulica atra) on the population of Dreissena polymorpha in winter 2001/2002. These three species, with monthly peak numbers of approximately 230 000 individuals, currently comprise up to 80% of the waterbird population wintering at Lake Constance. 2. Four different study sites and four depths, that represent typical and characteristic habitats of mussels in Upper Lake Constance, were chosen. 3. Zebra mussels were sampled before, during and after predation by waterbirds. Their biomass in shallow areas decreased by >90%; the biomass reduction in deeper areas was highly variable and dependent on the substratum. With one exception, no changes could be detected at the greatest depth (11 m). 4. Concurrent exclosure studies revealed that the decrease in zebra mussels was caused by waterbird predation. A GIS‐based approximation revealed that in an area of 1 km² a total of approximately 750 t mussel fresh mass was removed by birds, which is equivalent to 1390 g mussels per bird per day. 5. Wintering waterbirds have a strong structural impact on the littoral community of Lake Constance and could be the key predator of zebra mussels.     

Cyclic AMP and Calcium in Relaxation in Intestinal Smooth Muscle

WE have studied the role of cyclic AMP in relaxation of smooth muscle and elucidated the mechanism of its action.     

Prevalence of common <Emphasis Type="Italic">MEFV</Emphasis> mutations and carrier frequencies in a large cohort of Iranian populations

Familial Mediterranean fever (FMF) is a hereditary autoinflammatory disorder caused by mutations in the MEFV gene. The disease is especially common among Armenian, Turkish, Jewish and Middle East Arab populations. To identify the frequency and the spectrum of common MEFV mutations in different Iranian populations, we investigated a cohort of 208 unselected asymptomatic individuals and 743 FMF patients. Nine hundred and fifty-one samples were analysed for the presence of 12 MEFV mutations by PCR and reverse-hybridization (FMF StripAssay, ViennaLab, Vienna, Austria). Confirmatory dideoxy sequencing of all MEFV gene exons was performed for 39 patients. Fifty-seven (27.4%) healthy individual carried mutant MEFV alleles. Three hundred and ninety-one (52.6%) FMF patients were found positive for either one (172/743; 23.1%), two or three MEFV mutations. Using dideoxy sequencing, three novel variants, A66P, R202W and H300Q, could be identified. Our analysis revealed an allele frequency and carrier rate of 15.6 and 27.4%, respectively, among healthy Iranians. Still moderate compared to neighbouring Armenia, but higher than in Turkey or Iraq, these data suggest that FMF is remarkably common among Iranian populations. E148Q was most frequent in the group of healthy individuals, whereas M694V was the most common mutation among FMF patients, thereby corroborating previous studies on MEFV mutational spectra in the Middle East. Accordingly, MEFV mutations are frequent in healthy Iranian individuals across different ethnic groups. Based on this finding, the awareness for FMF and the implementation of augmented carrier screening programmes considering the multiethnic nature of the Iranian population should be promoted.     

Embryonic and post-embryonic development of the Early Cambrian cnidarian Olivooides

Phosphatized specimens of Olivooides from the Early Cambrian of Shaanxi, China, represent a number of developmental stages. These include cleavage, gastrulation, organogenesis, cuticularization, pre-hatching, post-hatching and subsequent growth. This allows the reconstruction of a nearly full developmental sequence of this animal. Olivooides had large (600-870 μm in diameter), sphaerical eggs, indicating a high yolk content. Development was direct. Thus adult characters were forming already in the embryo, and there was no free larval stage. The embryonic development took place within a smooth protective membrane. Gastrulation probably was by polar ingression, and the blastopore appears to correspond to the aperture of the later stages. An embryonic cuticle formed which carried star-shaped structures, stellae, over the entire surface except for a radially folded non-stellate portion around the future aperture. At a later stage, the stellate cuticle was thrown into folds concentric with the aperture. This radially folded tissue then became more dominant. After hatching, the body assumed the shape of a strongly annulated cone, with the stellate cuticle forming the apical part and the folded cuticle forming a longitudinally striate cuticle around the aperture. Subsequent growth took place through the addition of striate tissue. A pentaradial symmetry of the body is suggested by lateral folds in the apical part. Olivooides is interpreted as a cnidarian, probably closely related to the scyphozoans. The conical test may have housed a polyp similar to the thecate polyps of modern coronate scyphozoans, but, unlike the latter, Olivooides had no visible attachment structures. There is no evidence for or against a free medusa stage. The prevalence of lecithotrophic direct developers in the Neoproterozoic and Cambrian, unless reflecting a preservational bias, casts some doubts on evolutionary models that assume larval planktotrophy to be primitive among metazoans.     

RAPID ALDOSTERONE-INDUCED CELL VOLUME INCREASE OF ENDOTHELIAL CELLS MEASURED BY THE ATOMIC FORCE MICROSCOPE

Atomic force microscopy (AFM) is a useful technique for imaging the surface of living cells in three dimensions. The authors applied AFM to obtain morphological information of individual cultured endothelial cells of bovine aorta under stationary and strain conditions and to simultaneously measure changes in cell volume in response to aldosterone. This mineralocorticoid hormone is known to have acute, non-genomic effects on intracellular pH, intracellular electrolytes and inositol-1,4,5-triphosphate production. In this study whether endothelial cells under tension change their volume in response to aldosterone was tested. Such changes were already shown in human leukocytes measured by Coulter counter. In contrast to leukocytes that are more or less spherical and live in suspension, endothelial cells exhibit a complex morphology and adhere to a substrate. Thus, measurements of discrete cell volume changes in endothelial cells under physiological condition is only feasible with more sophisticated techniques. By using AFM we could precisely measure the absolute cell volume of individual living endothelial cells. Before the addition of aldosterone the cell volume of mechanically stressed endothelial cells mimicking arterial blood pressure was 1827±172fl. Cell volume was found to increase by 28% 5min after hormone exposure. Twenty-five minutes later cell volume was back to normal despite the continuous presence of aldosterone in the medium. Amiloride, a blocker of the plasma membrane Na⁺/H⁺exchanger prevented the initial aldosterone-induced volume increase. Taken together, AFM disclosed a transient swelling of endothelial cells induced by the activation of an aldosterone sensitive plasma membrane Na⁺/H⁺exchanger.     

Fire season effects on the recruitment of non‐sprouting serotinous Proteaceae in the eastern (bimodal rainfall) fynbos biome,South Africa

Abstract Research in Mediterranean‐climate shrublands in both South Africa and Australia shows that recruitment of proteoid shrubs (non‐sprouting, serotinous Proteaceae) is best after warm‐season (summer and autumn) fires and worst after cool‐season (winter and spring) ones. This pattern has been attributed to post‐dispersal seed attrition as well as size of pre‐dispersal seed reserves. Here we investigate patterns of post‐fire recruitment for four proteoid species in the eastern part of South Africa's fynbos biome, which has a bimodal (spring and autumn) rainfall regime. Despite the lack of significant differences in recruitment between cool‐ and warm‐season burns, we find some evidence for favourable recruitment periods following fires in spring and autumn, immediately before, and coinciding with, the bimodal rainfall peaks. This suggests that enhanced recruitment is associated with conditions of high soil moisture immediately after the fire, and that rapid germination may minimize post‐dispersal seed attrition. In two of the species, we also find a shift from peak flowering in winter and spring in the Mediterranean‐climate part of the fynbos biome, to summer and autumn flowering in the eastern part. Because these two species are only weakly serotinous, warm‐season flowering would result in maximal seed banks in spring, which could explain the spring recruitment peak, but not the autumn one. We conclude that eastern recruitment patterns differ significantly from those observed in the western and central parts of the biome, and that fire management protocols for the east, which are currently based on data and experience from the winter‐rainfall fynbos biome, need to be adjusted accordingly. Fire managers in the eastern fynbos biome should be less constrained by requirements to burn within a narrow seasonal range, and should therefore be in a better position to apply the required management burns.     

Galápagos' Opuntia (prickly pear) cacti: extensive morphological diversity, low genetic variability

Due to the pronounced morphological variation and geographical distribution of Galápagos' Opuntia cacti, numerous hypotheses have been advanced regarding their radiation, diversification, and classification. The currently accepted classification is based on morphology and recognizes six species and fourteen varieties, but the plasticity of many of the characteristics renders any morphological taxonomy problematic. Our analysis of previously published morphological data agrees only partially with the current classification. We present the first molecular phylogeny of these plants. Multiple DNA sequences indicate little genetic distinction among the currently identified species, despite restricted gene flow and limited long distance dispersal within the archipelago. No clear relationship exists between morphological and genetic differences. These results suggest that both molecular and morphological data should be used in conservation planning.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 451–461.     

Effects of an experimental drought on the functioning of a cacao agroforestry system,Sulawesi, Indonesia

Agroforestry systems may play a critical role in reducing the vulnerability of farmers' livelihood to droughts as tree‐based systems provide several mechanisms that can mitigate the impacts from extreme weather events. Here, we use a replicated throughfall reduction experiment to study the drought response of a cacao/Gliricidia stand over a 13‐month period. Soil water content was successfully reduced down to a soil depth of at least 2.5 m. Contrary to our expectations we measured only relatively small nonsignificant changes in cacao (?11%) and Gliricidia (?12%) sap flux densities, cacao leaf litterfall (+8%), Gliricidia leaf litterfall (?2%), soil carbon dioxide efflux (?14%), and cacao yield (?10%) during roof closure. However, cacao bean yield in roof plots was substantially lower (?45%) compared with control plots during the main harvest following the period when soil water content was lowest. This indicates that cacao bean yield was more sensitive to drought than other ecosystem functions. We found evidence in this agroforest that there is complementary use of soil water resources through vertical partitioning of water uptake between cacao and Gliricidia. This, in combination with acclimation may have helped cacao trees to cope with the induced drought. Cacao agroforests may thus play an important role as a drought‐tolerant land use in those (sub‐) tropical regions where the frequency and severity of droughts is projected to increase.