Turnover des flavonols dans les tuniques d'Allium cepa en survie

During ageing of isolated onion scales there is an accumulation of flavonols which increase continuously. This is not light-dependent but is associated with a high level of respiratory gaseous exchanges. Phenylalanine-[U-¹⁴C] is actively incorporated in these flavonols but experiments of pulse labelling show that they have either a very slow or no turnover. This suggests that enzymes able to destroy flavonols are lacking in this material.     

Ectocranial suture fusion in primates: pattern and phylogeny

Patterns of ectocranial suture fusion among Primates are subject to species‐specific variation. In this study, we used Guttman Scaling to compare modal progression of ectocranial suture fusion among Hominidae (Homo, Pan, Gorilla, and Pongo), Hylobates, and Cercopithecidae (Macaca and Papio) groups. Our hypothesis is that suture fusion patterns should reflect their evolutionary relationship. For the lateral‐anterior suture sites there appear to be three major patterns of fusion, one shared by Homo‐Pan‐Gorilla, anterior to posterior; one shared by Pongo and Hylobates, superior to inferior; and one shared by Cercopithecidae, posterior to anterior. For the vault suture pattern, the Hominidae groups reflect the known phylogeny. The data for Hylobates and Cercopithecidae groups is less clear. The vault suture site termination pattern of Papio is similar to that reported for Gorilla and Pongo. Thus, it may be that some suture sites are under larger genetic influence for patterns of fusion, while others are influenced by environmental/biomechanic influences. J. Morphol. 275:342–347, 2014. © 2013 Wiley Periodicals, Inc.     

Bird and mammal species composition in distinct geographic regions and their relationships with environmental factors across multiple spatial scales

Global patters of species distributions and their underlying mechanisms are a major question in ecology, and the need for multi‐scale analyses has been recognized. Previous studies recognized climate, topography, habitat heterogeneity and disturbance as important variables affecting such patterns. Here we report on analyses of species composition – environment relationships among different taxonomic groups in two continents, and the components of such relationships, in the contiguous USA and Australia. We used partial Canonical Correspondence Analysis of occurrence records of mammals and breeding birds from the Global Biodiversity Information Facility, to quantify relationships between species composition and environmental variables in remote geographic regions at multiple spatial scales, with extents ranging from 10⁵ to 10⁷ km² and sampling grids from 10 to 10,000 km². We evaluated the concept that two elements contribute to the impact of environmental variables on composition: the strength of species' affinity to an environmental variable, and the amount of variance in the variable. To disentangle these two elements, we analyzed correlations between resulting trends and the amount of variance contained in different environmental variables to isolate the mechanisms behind the observed relationships. We found that climate and land use‐land cover are responsible for most explained variance in species composition, regardless of scale, taxonomic group and geographic region. However, the amount of variance in species composition attributed to land use / land cover (LULC) was closely related to the amount of intrinsic variability in LULC in the USA, but not in Australia, while the effect of climate on species composition was negatively correlated to the variability found in the climatic variables. The low variance in climate, compared to LULC, suggests that species in both taxonomic groups have strong affinity to climate, thus it has a strong effect on species distribution and community composition, while the opposite is true for LULC.     

Spatiotemporal dimensions of community assembly

Ecological communities are assembled through a series of multiple processes, including dispersal, abiotic and biotic filtering, and ecological drift. Although these assembly processes act in concert to structure local communities, their relative importance is considerably variable among study systems. While such contingency of community assembly has been widely appreciated, the empirical and theoretical evidence is scattered around in the literature, and few efforts have been made to synthesize it. In this mini-review, we summarize the accumulated evidence of the context-dependency of community assembly rules, to reach a rough generalization of the contingency. Specifically, we argue that spatial and temporal dimensions can serve as general axes that regulate the relative importance of assembly processes. To this end, we synthesize the current understanding of how the relative importance of multiple assembly processes changes with spatial scales and complexity, and with time in the long and short terms. This review concludes that spatial and temporal dimensions can be common currencies of community assembly rules that are shared across various systems.     

Whole-Ecosystem Experiments: Replication Versus Realism: The Need for Ecosystem-Scale Experiments

The results of bottle and mesocosm experiments were compared with those obtained in whole-ecosystem experiments at the Experimental Lakes Area. Unless they can be cleverly designed to mimic major ecosystem processes and community compositions, smaller-scale experiments often give highly replicable, but spurious, answers. Problems with appropriate scaling are difficult to deduce without direct comparisons with whole-ecosystem experiments. Reasons are many, but include inappropriate spatial scales to include whole communities, in particular predators and nocturnally active animals; temporal scales that are too short to assess accurately the response of slow-responding organisms and biogeochemical processes; and elimination of key littoral–pelagic and catchment–lake interactions. Identical studies of limnological processes in lakes of a large range of sizes reveals that scaling correction is also necessary when extrapolating from small lakes to large ones. Accurate management decisions cannot be made with confidence unless ecosystem scales are studied. Received 26 March 1998; accepted 14 May 1998.     

Influence of aquatic macrophyte habitat complexity on invertebrate abundance and richness in tropical lagoons

1. Aquatic plants are a key component of spatial heterogeneity in a waterscape, contributing to habitat complexity and helping determine diversity at various spatial scales. Theoretically, the more complex a habitat, the higher the number of species present. 2. Few empirical data are available to test the hypothesis that complexity increases diversity in aquatic communities (e.g. Jeffries, 1993 ). Fractal dimension has become widely applied in ecology as a tool to quantify the degree of complexity at different scales. 3. We investigated the hypothesis that complexity in vegetated habitat in two tropical lagoons mediates littoral invertebrate number of taxa (S) and density (N). Aquatic macrophyte habitat complexity was defined using a fractal dimension and a gradient of natural plant complexities. We also considered plant area, plant identity and, only for S, invertebrate density as additional explanatory variables. 4. Our results indicate that habitat complexity provided by the different architectures of aquatic plants, significantly affects both S and total N. However, number of individuals (as a result of passive sampling) also helps to account for S and, together with plant identity and area, contributes to the determination of N. We suggest that measurements of structural complexity, measured through fractal geometry, should be included in studies aimed at explaining attributes of attached invertebrates at small (e.g. plant or leaf) scales.     

Variability in relative importance of determinants of reef fish recruitment

Multiple processes can act together to determine abundance of organisms and structure of communities. Recently, appreciation of this fact has motivated development of conceptual and statistical frameworks that quantitatively assess the relative importance of multiple causal factors. However, little consideration has been given to variability in the "importance" of processes through space and time (i.e. robustness), which represents another facet of a process's importance. Here, I focused on populations of a coral reef fish ( Thalassoma hardwicke ) and used an existing analytical method to assess the relative importance of initial population inputs (larval supply) and subsequent juvenile mortality in determining the average abundances of juvenile fish populations in different locations and times. The relative importance of processes varied significantly both temporally and spatially across a range of scales, and indicate a need for future assessments of relative importance to incorporate this variability.     

Silica-scaled chrysophytes (Synurophyceae) from some rivers and shallow lakes in Hungary

Silica-scaled chrysophytes are a special group in the phytoplankton of rivers and shallow lakes. They are present the whole year at low density, but sometimes — mainly during autumn and spring — some species can become frequent and very numerous to form real water blooms.In this study, seven species of silica-scaled chrysophytes have been recorded and identified by electron microscopy of phytoplankton samples from some rivers and shallow lakes in Hungary. Most of these silica-scaled chrysophytes have previously been found in eutrophic and hypertrophic localities, and almost all of them are common and widely distributed, even cosmopolitan. Only Synura echinulata Korshikov has not previously been recorded from Hungary. Some of them as Synura curtispina (Petersen & Hansen) Asmund, S. petersenii Korshikov, Mallomonas acaroides Perty emend. Ivanov, M. tonsurata Teiling were frequently found in the phytoplankton samples. Sometimes in autumn and winter Synura petersenii was the most abundant species in the phytoplankton and formed blooms.     

Siliceous scales in the centrohelid heliozoan Raphidocystis contractilis facilitate settlement to the substratum

The centrohelid heliozoan Raphidocystis contractilis has hundreds of small scales on the surface of the cell body. To understand the biological functions of the scales, comparative examinations were conducted between wild-type and scale-deficient strains that has naturally lost scales after long-term cultivation. The scale-deficient strain exhibited decreased adhesion to the substratum and had a lower sedimentation rate in water than the wild-type strain, suggesting that the scale may have the ability to attach quickly and strongly to the substratum. Percoll density gradient centrifugation showed that the scale-deficient strain had a lower density than that of the wild-type strain. In the wild-type strain, more scaled cells were observed in the higher specific gravity fractions. During the long-term culture of cells, only the cells suspended in the upper area of the flask were transferred to fresh medium. By repeating this procedure, we may have selected only cells that did not possess normal scales. In the natural environment, centrohelid heliozoans are easily flushed away if they cannot adhere strongly to the bottom. These results suggest that they use scales to ensure effective adhesion to the substratum.