West versus East Mediterranean Sea: origin and genetic differentiation of the sea cucumber Holothuria polii          下载免费PDF全文

Sara Valente  Ester A. Serrão  Mercedes González‐Wangüemert 《Marine Ecology》2015,36(3):485-495

We studied the genetic structure of the sea cucumber Holothuria (Roweothuria) polii (Delle Chiaje 1823) by analysing the mitochondrial DNA variation in two fragments of cytochrome oxidase I (COI) and 16S genes. Individuals were collected in seven locations along the Mediterranean Sea, which cover a wide range of the species distribution. We found high haplotype diversity for COI and moderate diversity for 16S, and low nucleotide diversity for both genes. Our results for the COI gene showed many recent and exclusive haplotypes with few mutational changes, suggesting recent or ongoing population expansion. The Western and Eastern Mediterranean populations exhibited slight but significant genetic differentiation (COI gene) with higher genetic diversity in the East. The most ancient haplotype was not present in the westernmost sampling location (SE Spain). The oldest expansion time was observed in Turkey, corresponding to mid‐Pleistocene. Turkey had also the highest genetic diversity (number of total and exclusive haplotypes, polymorphisms, haplotype and nucleotide diversity). This suggests that this region could be the origin of the subsequent colonizations through the Mediterranean Sea, a hypothesis that should be assessed with nuclear markers in future research.  相似文献   

Imposex levels and concentrations of organotin compounds (TBT and its metabolites) in Nassarius nitidus from the Lagoon of Venice   总被引：1，自引：0，他引：1  

Pavoni B  Centanni E  Valcanover S  Fasolato M  Ceccato S  Tagliapietra D 《Marine pollution bulletin》2007,55(10-12):505-511

Specimens of Nassarius nitidus were collected in seven stations of the Venice Lagoon to assess the levels of tributyltin (TBT) and its metabolites monobutyltin and dibutyltin in the tissues and monitor their effect on organisms, in particular the phenomenon of imposex (superimposition of male sexual characteristics on females). The following values of population indices were found: vas deferens sequence: 1.2+/-0.7-4.0+/-0.5; relative penis length: 6-47%. The least impacted station was situated in the northern part of the Lagoon, where females without imposex were found and Butyltin (BuTs) concentrations in the organisms (average sum of BuTs=43+/-14 ngSng(-1)w.) were significantly lower than in the other stations (range of average sum of BuTs: 101+/-22-217+/-27 ngSng(-1)d.w.). Population indices were found to be related to the TBT content in the tissues. In particular VDSI had a significant logarithmic correlation: r=0.95, n=8, p<0.05.  相似文献   

Compact groups in theory and practice – II. Comparing the observed and predicted nature of galaxies in compact groups     

Crystal M. Brasseur  Alan W. McConnachie  Sara L. Ellison  David R. Patton 《Monthly notices of the Royal Astronomical Society》2009,392(3):1141-1152

We examine the properties of galaxies in compact groups (CGs) identified in a mock galaxy catalogue based upon the Millennium Run simulation. The overall properties of groups identified in projection are in general agreement with the best available observational constraints. However, only ∼30 per cent of these simulated groups are found to be truly compact in three dimensions, suggesting that interlopers strongly affect our observed understanding of the properties of galaxies in CGs. These simulations predict that genuine CG galaxies are an extremely homogeneous population, confined nearly exclusively to the red sequence: they are best described as 'red and dead' ellipticals. When interlopers are included, the population becomes much more heterogeneous, due to bluer, star-forming, gas-rich, late-type galaxies incorrectly identified as CG members. These models suggest that selection of members by redshift, such that the line-of-sight velocity dispersion of the group is less than 1000 km s⁻¹, significantly reduces contamination to the 30 per cent level. Selection of members by galaxy colour, a technique used frequently for galaxy clusters, is also predicted to dramatically reduce contamination rates for CG studies.  相似文献   

Extension and Intensification of the Meso-American mid-summer drought in the twenty-first century     

Sara A. Rauscher  Filippo Giorgi  Noah S. Diffenbaugh  Anji Seth 《Climate Dynamics》2008,31(5):551-571

Recent global-scale analyses of the CMIP3 model projections for the twenty-first century indicate a strong, coherent decreased precipitation response over Central America and the Intra-America Seas region. We explore this regional response and examine the models’ skill in representing present-day climate over this region. For much of Central America, the annual cycle of precipitation is characterized by a rainy season that extends from May to October with a period of reduced precipitation in July and August called the mid-summer drought. A comparison of the climate of the twentieth century simulations (20c3m) with observations over the period 1961–1990 shows that nearly all models underestimate precipitation over Central America, due in part to an underestimation of sea surface temperatures over the tropical North Atlantic and an excessively smooth representation of regional topographical features. However, many of the models capture the mid-summer drought. Differences between the A1B scenario (2061–2090) and 20c3m (1961–1990) simulations show decreased precipitation in the future climate scenario, mostly in June and July, just before and during the onset of the mid-summer drought. We thus hypothesize that the simulated twenty-first century drying over Central America represents an early onset and intensification of the mid-summer drought. An analysis of circulation changes indicates that the westward expansion and intensification of the North Atlantic subtropical high associated with the mid-summer drought occurs earlier in the A1B simulations, along with stronger low-level easterlies. The eastern Pacific inter-tropical convergence zone is also located further southward in the scenario simulations. There are some indications that these changes could be forced by ENSO-like warming of the tropical eastern Pacific and increased land–ocean heating contrasts over the North American continent.  相似文献   

CMIP3 projected changes in the annual cycle of the South American Monsoon     

Anji Seth  Maisa Rojas  Sara A. Rauscher 《Climatic change》2010,98(3-4):331-357

Nine models from the Coupled Model Intercomparison Project version 3 dataset are employed to examine projected changes in the South American Monsoon System annual cycle by comparing the 20th Century and SRES A2 scenarios. The following hypotheses are examined: (1) the warm season climate responses in the Southeast, Continental South Atlantic Convergence Zone (CSACZ) and Monsoon regions are related by regional circulation and moisture transport changes which, in turn, must be consistent with robust large-scale changes in the climate system, and (2) an increased threshold for convection in a warmer world may affect the timing of warm season rains. The present analysis reaffirms that the Southeast region is likely to experience increased precipitation through the warm season. Additional results exhibit more uncertainty due to large inter-model variance and disagreement in the A2 scenarios. Nevertheless several statistically significant results are found. In the Monsoon and to a lesser extent in the CSACZ region, the multi-model median suggests reduced precipitation during spring (Sep–Nov). These continental precipitation changes are accompanied by a southward shift of the maximum precipitation in the South Atlantic Convergence Zone. Changes in circulation include a poleward displaced South Atlantic Anticyclone (SAAC) and enhanced moisture transport associated with a strengthened northerly low level flow east of the Andes during spring. Moisture transport divergence calculations indicate unchanged divergence in the Monsoon region during spring and increased convergence in the Southeast throughout the warm season. The circulation and moisture transport changes suggest the increased precipitation in the Southeast during spring may be related to changes in the SALLJ and SAAC, which both enhance moisture transport to the Southeast. The seasonally dry Monsoon region is further affected by an increased threshold for convection in the warmer, more humid and stable climate of the 21st century, which combined with the circulation changes may weaken the onset of the rainy season. Although there is substantial variability among the models, and the results are represented by small changes compared with the multi-model variance, their statistical significance combined with their consistency with expected robust large scale changes provides a measure of confidence in otherwise tentative results. Further testing of the relationships presented here will be required to fully understand projected changes in the South American Monsoon.  相似文献   

Remotely sensed soil moisture integration in an ecosystem carbon flux model. The spatial implication     

Willem W. Verstraeten  Frank Veroustraete  Wolfgang Wagner  Tom Van Roey  Walter Heyns  Sara Verbeiren  Jan Feyen 《Climatic change》2010,103(1-2):117-136

While remote sensing is able to provide spatially explicit datasets at regional to global scales, extensive application to date has been found only in the reporting and verification of ecosystem carbon fluxes under the Kyoto Protocol. One of the problems is that new remote sensing datasets can be used only with models or data assimilation schemes adapted to include a data input interface dedicated to the type and format of these remote sensing datasets. In this study, soil water index data (SWI), derived from the ERS scatterometer (10-daily time period with a spatial resolution of 50 km), are integrated into the ecosystem carbon balance model C-Fix to assess 10-daily Net Ecosystem Productivity (NEP) patterns of Europe from the remote sensing perspective on an approximate 1-by-1 km² pixel scale using NDVI-AVHRR data. The modeling performance of NEP obtained with and without the assimilation of remotely sensed soil moisture data in the carbon flux model C-Fix is evaluated with EUROFLUX data. Results show a general decrease of the RRMSE of up to 11 with an average of 3.46. C-Fix is applied at the European scale to demonstrate the potential of this ecosystem carbon flux model, based on remote sensing inputs. More specifically, the strong impact of soil moisture on the European carbon balance in the context of the Kyoto Protocol (anthropogenic carbon emissions) is indicated at the country level. Results suggest that several European countries shift from being a carbon sink (i.e., NEP > 1) to being a carbon source (i.e., NEP < 0) whether or not short-term water availability (i.e., soil moisture) is considered in C-Fix NEP estimations.  相似文献   

Comparison of classification and clustering methods in spatial rainfall pattern recognition at Northern Iran   总被引：1，自引：1，他引：0  

Saeed Golian  Bahram Saghafian  Sara Sheshangosht  Hossein Ghalkhani 《Theoretical and Applied Climatology》2010,102(3-4):319-329

Pattern recognition is the science of data structure and its classification. There are many classification and clustering methods prevalent in pattern recognition area. In this research, rainfall data in a region in Northern Iran are classified with natural breaks classification method and with a revised fuzzy c-means (FCM) algorithm as a clustering approach. To compare these two methods, the results of the FCM method are hardened. Comparison proved overall coincidence of natural breaks classification and FCM clustering methods. The differences arise from nature of these two methods. In the FCM, the boundaries between adjacent clusters are not sharp while they are abrupt in natural breaks method. The sensitivity of both methods with respect to rain gauge density was also analyzed. For each rain gauge density, percentage of boundary region and hardening error are at a minimum in the first cluster while the second cluster has the maximum error. Moreover, the number of clusters was sensitive to the number of stations. Since the optimum number of classes is not apparent in the classification methods and the boundary between adjacent classes is abrupt, use of clustering methods such as the FCM method, overcome such deficiencies. The methods were also applied for mapping an aridity index in the study region where the results revealed good coincidence between the FCM clustering and natural breaks classification methods.  相似文献   

Resolution effects on regional climate model simulations of seasonal precipitation over Europe   总被引：5，自引：2，他引：3  

Sara A. Rauscher  Erika Coppola  Claudio Piani  Filippo Giorgi 《Climate Dynamics》2010,35(4):685-711

We analyze a set of nine regional climate model simulations for the period 1961–2000 performed at 25 and 50 km horizontal grid spacing over a European domain in order to determine the effects of horizontal resolution on the simulation of precipitation. All of the models represent the seasonal mean spatial patterns and amount of precipitation fairly well. Most models exhibit a tendency to over-predict precipitation, resulting in a domain-average total bias for the ensemble mean of about 20% in winter (DJF) and less than 10% in summer (JJA) at both resolutions, although this bias could be artificially enhanced by the lack of a gauge correction in the observations. A majority of the models show increased precipitation at 25 km relative to 50 km over the oceans and inland seas in DJF, JJA, and ANN (annual average), although the response is strongest during JJA. The ratio of convective precipitation to total precipitation decreases over land for most models at 25 km. In addition, there is an increase in interannual variability in many of the models at 25 km grid spacing. Comparison with gridded observations indicates that a majority of models show improved skill in simulating both the spatial pattern and temporal evolution of precipitation at 25 km compared to 50 km during the summer months, but not in winter or on an annual mean basis. Model skill at higher resolution in simulating the spatial and temporal character of seasonal precipitation is found especially for Great Britain. This geographic dependence of the increased skill suggests that observed data of sufficient density are necessary to capture fine-scale climate signals. As climate models increase their horizontal resolution, it is thus a key priority to produce high quality fine scale observations for model evaluation.  相似文献   

The host galaxies of strong Ca ii quasar absorption systems at z < 0.5     

Berkeley J. Zych  Michael T. Murphy  Max Pettini  Paul C. Hewett  Emma V. Ryan-Weber  Sara L. Ellison 《Monthly notices of the Royal Astronomical Society》2007,379(4):1409-1422

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Agricultural performance on marginal land in Eastern Inner Mongolia,China – Development in the pre- and post-1978 reform periods     

Sara Brogaard  Xiubin Li 《GeoJournal》2005,64(3):163-175

Rapid economic development in the aftermath of the Chinese post-1978 reforms has resulted in a shrinking of grain grown area in the southern and eastern regions of the country which in turn is believed to have put the marginal northern regions under increased pressure. This paper examines key indicators of agricultural performance as well as cultivated land area development of the pre- and post-1978 reform periods focusing on the agro-pastoral Tongliao City Prefecture, eastern Inner Mongolia. The results are related to the village level development through a case study as well as to the provincial level. Average annual grain per capita production increased from about 400 kg in the late 1970s to more then 1000 kg in the late 1990s. This was achieved through a combination of intensification and reclamation of cropland, with the latter restricted to pastoral classified counties. Production variability, in particular for the low producing counties, has also increased possibly as an effect of the substitution of traditional mixed pattern of crops with HYV monocultures. Average living standards have improved but have been accompanied by widening income gaps. Poor farmers’ livelihoods continue to be insecure, particularly during dry years. Concern is raised regarding the sustainability of the rapid agricultural development; an increased use of costly fertilisers constrains poorer farmer’s economy and may lead to deteriorating water quality while increasing irrigation depletes water resources.  相似文献