Elevational Gradients in β-Diversity Reflect Variation in the Strength of Local Community Assembly Mechanisms across Spatial Scales

Despite long-standing interest in elevational-diversity gradients, little is known about the processes that cause changes in the compositional variation of communities (β-diversity) across elevations. Recent studies have suggested that β-diversity gradients are driven by variation in species pools, rather than by variation in the strength of local community assembly mechanisms such as dispersal limitation, environmental filtering, or local biotic interactions. However, tests of this hypothesis have been limited to very small spatial scales that limit inferences about how the relative importance of assembly mechanisms may change across spatial scales. Here, we test the hypothesis that scale-dependent community assembly mechanisms shape biogeographic β-diversity gradients using one of the most well-characterized elevational gradients of tropical plant diversity. Using an extensive dataset on woody plant distributions along a 4,000-m elevational gradient in the Bolivian Andes, we compared observed patterns of β-diversity to null-model expectations. β-deviations (standardized differences from null values) were used to measure the relative effects of local community assembly mechanisms after removing sampling effects caused by variation in species pools. To test for scale-dependency, we compared elevational gradients at two contrasting spatial scales that differed in the size of local assemblages and regions by at least an order of magnitude. Elevational gradients in β-diversity persisted after accounting for regional variation in species pools. Moreover, the elevational gradient in β-deviations changed with spatial scale. At small scales, local assembly mechanisms were detectable, but variation in species pools accounted for most of the elevational gradient in β-diversity. At large spatial scales, in contrast, local assembly mechanisms were a dominant force driving changes in β-diversity. In contrast to the hypothesis that variation in species pools alone drives β-diversity gradients, we show that local community assembly mechanisms contribute strongly to systematic changes in β-diversity across elevations. We conclude that scale-dependent variation in community assembly mechanisms underlies these iconic gradients in global biodiversity.     

Diversity,Abundance, and Spatial Distribution of Ammonia-Oxidizing β-Proteobacteria in Sediments from Changjiang Estuary and Its Adjacent Area in East China Sea

Changjiang Estuary, the largest estuary in China, encompasses a wide range of nutrient loading and trophic levels from the rivers to the sea, providing an ideal natural environment to explore relationships between functional diversity, physical/chemical complexity, and ecosystem function. In this study, molecular biological techniques were used to analyze the community structure and diversity of ammonia-oxidizing bacteria (AOB) in the sediments of Changjiang Estuary and its adjacent waters in East China Sea. The amoA gene (encoding ammonia monooxygenase subunit A) libraries analysis revealed extensive diversity within the β-Proteobacteria group of AOB, which were grouped into Nitrosospira-like and Nitrosomonas-like lineages. The majority of amoA gene sequences fell within Nitrosospira-like clade, and only a few sequences were clustered with the Nitrosomonas-like clade, indicating that Nitrosospira-like lineage may be more adaptable than Nitrosomonas-like lineage in this area. Multivariate statistical analysis indicated that the spatial distribution of the sedimentary β-Proteobacterial amoA genotype assemblages correlated significantly with nitrate, nitrite, and salinity. The vertical profile of amoA gene copies in gravity cores showed that intense sediment resuspension led to a deeper mixing layer. The horizontal distribution pattern of amoA gene copies was nearly correlated with the clayey mud belt in Changjiang Estuary and its adjacent area in East China Sea, where higher β-Proteobacteria phylogenetic diversity was observed. Meanwhile, those areas with high amoA copies in the surface sediments nearly matched those with low concentrations of dissolved oxygen and ammonium in the bottom water.     

Characterization of the mRNAs for α-, β- and γ-actin

The mRNAs for α-, β- and γ-actin have been characterized with respect to molecular weight and poly(A) content. Polyacrylamide gel electrophoresis under denaturing conditions shows that the mRNA for α-actin (muscle-specific actin) is approximately 4.6 × 10⁵ daltons in size, and that the mRNAs for β- and γ-actin (nonmuscle actins) are much larger, approximately 6.6 × 10⁵ daltons in size. We therefore calculate that the noncoding regions of the β- and γ-actin mRNAs contain about 800 nucleotides. This is in marked contrast to the noncoding regions of α-actin mRNA which contain only about 180 nucleotides. During electrophoresis in high-resolution nondenaturing gels, the β-actin mRNA migrates slightly slower than the γ-actin mRNA. This indicates either that β-actin mRNA is about 100 nucleotides longer than γ-actin mRNA, or that these mRNAs differ in secondary structure. Fractionation of actin mRNA on the basis of poly(A) content shows that a substantial portion of the β-actin mRNA, but very little of the α- or γ-actin mRNAs, fails to bind to oligo(dT)-cellulose. Much of this poly(A)-deficient β-actin mRNA, however, does bind to poly(U)-Sepharose, a substrate with higher affinity for short poly(A) sequences. This indicates that many of these β-actin mRNA molecules are polyadenylated, but that they have unusually short poly(A) tails. The finding that β- and γ-actins are translated from mRNAs of different electrophoretic mobility and different poly(A) content strongly suggests that these two closely related proteins are products of different genes.     

Ultrastructural localization of corticotropin, β-lipotropin,and αand β-endorphin in the porcine anterior pituitary

Summary The peroxidase-antiperoxidase immunocytochemical technique was used to identify the ACTH/endorphin cells in the porcine pituitary at the ultrastructural level and to determine the precise subcellular localization of the pro-ACTH/endorphin fragments. The cells display different aspects: 1) large, regular shapes with numerous and large secretory granules; 2) small, irregular and angular shapes with small granules aligned along the periphery of the cell; and 3) intermediate forms. The presence of and -endorphin not only in the same cells but also in the same secretory granules that contain ACTH and -LPH clearly indicates that both the precursor or its fragments and the abovementioned peptides are stored in the same granules and released simultaneously by the corticotropic cells. The presence of FSH in some corticotropic cells is also discussed.Abbreviations used in this Article ACTH corticotropin - -MSH -melanotropin (ACTH I–I3) - CLIP corticotropin-like intermediate lobe peptide (ACTH 18–39) - -LPH -lipotropin - -MSH -melanotropin (-LPH 41–58); -endorphin (-LPH 61–91); -endorphin (-LPH 61–76)     

The localization and the isoenzymes of α- and β-Galactosidases in root tips

The localization was studied of α- and β-galactosidases in frozen sections of Ca-formol fixed root tips using simultaneous azocoupling reaction. In all species studied (Allium cepa,Cucurbita maxima, Lupinus albus, Pisum sativum, Vicia faba, Zea mays) positive results were obtained, the localization being ubiquitous (according to localization typology given here). InVicia faba andZea mays the isoenzymes of α- and β-galactosidases were revealed by means of acrylamide gel electrophoresis, using authors’ modification of Reisfeld method, in whole root tips, particular growth zones and separately in cortex and central cylinder. No differences were observed comparing stele and cortex. Whereas characteristic isoenzyme patterns were found in individual growth zones in maize, no differences appeared in broad bean. A comparison was made of thein situ localization and of the isoenzyme patterns of α- and β-galactosidases with α- and β-glucosidases. In the case of galactosidases, positive results appear with both α- and β-galactoside. The rising of pH to neutrality leads to considerable decrease in the activity of both galactosidases.     

Spatio-Temporal Variability of Copepod Abundance along the 20°S Monitoring Transect in the Northern Benguela Upwelling System from 2005 to 2011

Long-term data sets are essential to understand climate-induced variability in marine ecosystems. This study provides the first comprehensive analysis of longer-term temporal and spatial variations in zooplankton abundance and copepod community structure in the northern Benguela upwelling system from 2005 to 2011. Samples were collected from the upper 200 m along a transect at 20°S perpendicular to the coast of Namibia to 70 nm offshore. Based on seasonal and interannual trends in surface temperature and salinity, three distinct time periods were discernible with stronger upwelling in spring and extensive warm-water intrusions in late summer, thus, high temperature amplitudes, in the years 2005/06 and 2010/11, and less intensive upwelling followed by weaker warm-water intrusions from 2008/09 to 2009/10. Zooplankton abundance reflected these changes with higher numbers in 2005/06 and 2010/11. In contrast, zooplankton density was lower in 2008/09 and 2009/10, when temperature gradients from spring to late summer were less pronounced. Spatially, copepod abundance tended to be highest between 30 and 60 nautical miles off the coast, coinciding with the shelf break and continental slope. The dominant larger calanoid copepods were Calanoides carinatus, Metridia lucens and Nannocalanus minor. On all three scales studied, i.e. spatially from the coast to offshore waters as well as temporally, both seasonally and interannually, maximum zooplankton abundance was not coupled to the coldest temperature regime, and hence strongest upwelling intensity. Pronounced temperature amplitudes, and therefore strong gradients within a year, were apparently important and resulted in higher zooplankton abundance.     

Ultrastructural localization of immunoreactive corticotropin, β-lipotropin, α- and β-endorphin in Cells of the human fetal anterior pituitary

Summary Cells immunoreactive with anti--(17–39) ACTH, -(1–24) corticotropin, -LPH, - and -EP were identified in the human fetal anterior pituitary at the ultrastructural level using the peroxidase-antiperoxidase complex method on ultrathin sections.Only one definite cell type was revealed by all these antisera. All granules of each individual immunostained cell reacted regardless of the antiserum used. The immunostained cells occurred in groups and were sometimes located in the wall of the follicle-like structures commonly observed in the fetal anterior pituitary. The cells revealed two main aspects: 1) The largest elements were rich in organelles, and their numerous secretory granules showed significant variations in size (250–500 nm in diameter), electron density of their content and stain-deposit intensity. The ergastoplasm, consisting of irregular tubules, was poorly developed. In the vicinity of the conspicuous Golgi apparatus, organelles related to the GERL complex were commonly observed. Multivesicular bodies were frequent. Some of these cells showed bundles of microfilaments (60 nm in thickness). 2) The smaller cells had an electron-lucent hyaloplasm with sparse organelles; they contained fewer granules and never showed microfilaments.The immunocytological results are consistent with the synthesis of a molecule similar to pro-opiocortin by this type of endocrine cell in human fetuses. Morphological evidence for the maturation process of this precursor and for the secretory activity of these cells and its possible regulation is presented and discussed.Abbreviations used ACTH corticotropin (39 amino acid polypeptide) - -MSH -melanotropin (ACTH [1–13]) - CLIP corticotropin-like intermediate lobe peptide (ACTH [18–39]) - -LPH -lipotropin (91 amino acid polypeptide) - -MSH -melanotropin (-LPH [41–58]) - -EP -endorphin (-LPH [61–91]) - -EP -endorphin (-LPH [61–76]) - PTA phosphotungstic acid Acknowledgements: The authors would like to thank Professors P. Magnin and J. Liaras, Hôpital Edouard Herriot; M. Dumont, Hôpital de la Croix-Rousse; A. Notter and R. Garmier, Hôtel Dieu; M. Bethenod, Hôpital Debrousse, Lyon, and the entire staff whose cooperation enabled samples to be taken under optimal conditions. The authors also thank Professor L. Graf, Research Institute for Pharmaceutical Chemistry (Budapest), and Professor R. Guillemin (Salk Institute, La Jolla) for their generous gift of antigensThis work was supported by a grant from I.N.S.E.R.M., ATP 46.77.78 (P.M. Dubois)     

Conformational stabilities of the rat α- and β-parvalbumins

It is widely believed that β-parvalbumin (PV) isoforms are intrinsically less stable than α-parvalbumins, due to greater electrostatic repulsion and an abbreviated C-terminal helix. However, when examined by differential scanning calorimetry, the apo-form of the rat β-PV (i.e. oncomodulin) actually displays greater thermal stability than the α-PV. Whereas the melting temperature of the α isoform is 45.8°C at physiological pH and ionic strength, the T_m for the β isoform is more than 7° higher (53.6°C). This result suggests that factors besides net charge and C-terminal helix length strongly influence parvalbumin conformational stability. Extension of the F helix in the β-PV, by insertion of Ser-109, has a modest stabilizing effect, raising the T_m by 1.1°. Truncation of the α-PV F helix, by removal of Glu-108, has a more profound impact, lowering the T_m by 4.0°.     

Ontogeny and localization of the α, β, and γ crystallins in newt eye lens development

The α-, β-, and γ-crystallins, proteins characteristic for the vertebrate eye lens, have been localized in the developing lens of Notophthalmus viridescens, the eastern spotted newt. Using the immunofluorescence technique, antibodies to the α-, β-, and γ-crystallin classes were applied to tissue sections through the eye region of developing N. viridescens embryos, Harrison (external) Stages 30 to 46+. β-Crystallins were the first of the crystallins to appear in a few cells of the lens vesicle even before the lengthening of the prospective primary fiber cells. γ-Crystallins were first detectable at a slightly more advanced stage in the prospective primary fibers, and α-crystallins in a few cells of the beginning primary fiber area. The external layer/epithelium was negative for β-crystallins until late in lens morphogenesis, and α- and γ-crystallins could not be detected in these cells at any time. This, the first use in amphibia of homologous antibodies specific for the crystallin classes, makes clear that phylogenetic differences exist as to the primacy and relevance of specific crystallins to events during morphogenesis of the eye lens.     

Enzymatic Activities and Prokaryotic Abundance in Relation to Organic Matter along a West–East Mediterranean Transect (TRANSMED Cruise)

The distribution of extracellular enzymatic activities (EEA) [leucine aminopeptidase (LAP), ?-glucosidase (GLU), alkaline phosphatase (AP)], as well as that of prokaryotic abundance (PA) and biomass (PB), dissolved organic carbon (DOC), particulate organic carbon and particulate total nitrogen (POC, PTN), was determined in the epi-, meso-, and bathypelagic waters of the Mediterranean Sea along a West-East transect and at one Atlantic station located outside the Strait of Gibraltar. This study represents a synoptical evaluation of the microbial metabolism during early summer. Decreasing trends with depth were observed for most of the parameters (PA, PB, AP, DOC, POC, PTN). Significant differences between the western and eastern basins of the Mediterranean Sea were found, displaying higher rates of LAP and GLU and lower C/N ratios more in the eastern than in the western areas. Conversely, in the epipelagic layer, PA and PB were found to be higher in the western than in the eastern basins. PB was significantly related to DOC concentration (all data, n = 145, r = 0.53, P < 0.01), while significant correlations of EEA with POC and PTN were found in the epipelagic layer, indicating an active response of microbial metabolism to organic substrates. Specific enzyme activities normalized to cell abundance pointed out high values of LAP and GLU in the bathypelagic layer, especially in the eastern basin, while cell-specific AP was high in the epi- and bathypelagic zone of the eastern basin indicating a rapid regeneration of inorganic P for both prokaryotes and phytoplankton needs. Low activity and abundance characterized the Atlantic station, while opposite trends of these parameters were observed along the Mediterranean transect, showing the uncoupling between abundance and activity data. In the east Mediterranean Sea, decomposition processes increased probably in response to mesoscale structures which lead to organic matter downwelling.     

The evolution of the α- and β-globin gene clusters in human populations

Summary DNA analysis of the - and -globin gene clusters has revealed substantial variability between individuals and populations. As well as restriction enzyme site and length polymorphisms, variation in gene copy number and type is observed. Because of this extensive polymorphism DNA analysis offers a highly informative method of studying genetic affinities between human populations. Haplotypes, consisting of a set of restriction enzyme polymorphisms distributed along the cluster, have been developed for both loci. Analysis of the molecular basis of numerous -thalassaemia alleles has revealed, in general, different sets of mutations in different populations, indicating that these postdate the racial divergence. Recent microepidemiological studies on the distribution of -thalassaemia support the hypothesis that this condition, like the {ie16-1}, has been selected because it confers protection against malaria. Population-specific DNA polymorphisms at these and other loci promise to be of considerable value to genetic anthropology.     

T3 regulates E-cadherin,and β- and α-catenin expression in the stomach during the metamorphosis of the toad Rhinella arenarum

Abstract

The metamorphosis of Rhinella arenarum was induced precociously for 5 days, then blocked for 3 months to evaluate the role of thyroid hormones as modulators of morphoregulatory molecules such as E-cadherin, and β- and α-catenin during epithelium remodeling. We then performed an immunohistochemical and morphometric study of these molecules in the larval stomach. We show that 3,5,3′-triiodothyronine exerts a positive regulatory effect on E-cadherin and β- and α-catenin expression in stomach epithelium. This suggests continuous synthesis of E-cadherin, and β- and α-catenin; synthesis essentially is thyroid hormone-independent during premetamorphosis and early prometamorphosis, but it becomes thyroid hormone-dependent during metamorphic climax.     

Salecan Enhances the Activities of β-1,3-Glucanase and Decreases the Biomass of Soil-Borne Fungi

Salecan, a linear extracellular polysaccharide consisting of β-1,3-D-glucan, has potential applications in the food, pharmaceutical and cosmetic industries. The objective of this study was to evaluate the effects of salecan on soil microbial communities in a vegetable patch. Compositional shifts in the genetic structure of indigenous soil bacterial and fungal communities were monitored using culture-dependent dilution plating, culture-independent PCR-denaturing gradient gel electrophoresis (DGGE) and quantitative PCR. After 60 days, soil microorganism counts showed no significant variation in bacterial density and a marked decrease in the numbers of fungi. The DGGE profiles revealed that salecan changed the composition of the microbial community in soil by increasing the amount of Bacillus strains and decreasing the amount of Fusarium strains. Quantitative PCR confirmed that the populations of the soil-borne fungi Fusarium oxysporum and Trichoderma spp. were decreased approximately 6- and 2-fold, respectively, in soil containing salecan. This decrease in the amount of fungi can be explained by salecan inducing an increase in the activities of β-1,3-glucanase in the soil. These results suggest the promising application of salecan for biological control of pathogens of soil-borne fungi.     

Differences between α- and β-Chain Mutants of Human Haemoglobin and between α- and β-Thalassaemia. Possible Duplication of the α-Chain Gene

Human adult haemoglobin consists of two unlike pairs of polypeptide chains, and can be described as α₂β₂. Amino-acid substitutions in either of the two types of chain result in α- and β-chain variants. In thalassaemia, which causes a lowered production of haemoglobin, the α or the β chain can be affected, the result being α- or β-thalassaemia. There is a quantitative difference in the proportion of α- and β-chain variants to normal haemoglobin in the respective heterozygotes, and there is also a difference in the pattern of inheritance of α- and β-thalassaemia: these could possibly be explained by assuming that man has one gene for the β- and two for the α-chain.     

Immunologie localization of α- and β-endorphins and β-lipotropin in corticotropic cells of the normal and anencephalic fetal pituitaries

Summary Intercellular bridges have been detected in ovarian follicle cells of Drosophila melanogaster. These bridges occur widely between follicle cells of previtellogenic chambers, while, in vitellogenic chambers, they become restricted to the columnar follicle cells. Usually, only one bridge is detectable between adjacent follicle cells, but a single cell may form two cytoplasmic continuities.The fine structure of the intercellular bridges is similar to that previously described in the development of Drosophila. The bridge wall consists of two layers of which the more external is more electron dense and thinner than the inner one.The role played by the intercellular bridges in the determination of a synchronous differentiation of the linked follicle cells is discussed in relation to the known behaviour of these cells in the secretion of the egg covering precursors.