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41.
RAFAEL M. ALVES ALEXANDRE M. SEBBENN ANGELA S. ARTERO ANTONIO FIGUEIRA 《Molecular ecology resources》2006,6(4):1219-1221
Theobroma grandiflorum (cupuassu) is an important fruit tree native to the Brazilian Amazon. Forty‐eight microsatellite loci developed for the congener Theobroma cacao were tested in cupuassu, and 29 (60.4%) produced robust alleles. The analyses of 216 cupuassu accessions using the 21 polymorphic microsatellite loci revealed a total of 113 alleles. The number of alleles per polymorphic locus ranged from two to 11, with an average of 5.38 alleles per locus. The average observed heterozygosity was 0.343, while the mean expected heterozygosity was 0.614. The successful transferability of T. cacao microsatellite primers to cupuassu was consistent with currently accepted phylogeny. 相似文献
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The oxygen isotope composition (δ18O) of atmospheric CO2 is among a very limited number of tools available to constrain estimates of the biospheric gross CO2 fluxes, photosynthesis and respiration at large scales. However, the accuracy of the partitioning strongly depends on the extent of isotopic disequilibrium between the signals carried by these two gross fluxes. Chamber‐based field measurements of total CO2 and CO18O fluxes from foliage and soil can help evaluate and refine our models of isotopic fractionation by plants and soils and validate the extent and pattern of isotopic disequilibrium within terrestrial ecosystems. Owing to sampling limitations in the past, such measurements have been very rare and covered only a few days. In this study, we coupled automated branch and soil chambers with tuneable diode laser absorption spectroscopy techniques to continuously capture the δ18O signals of foliage and soil CO2 exchange in a Pinus pinaster Aït forest in France. Over the growing season, we observed a seasonally persistent isotopic disequilibrium between the δ18O signatures of net CO2 fluxes from leaves and soils, except during rain events when the isotopic imbalance became temporarily weaker. Variations in the δ18O of CO2 exchanged between leaves, soil and the atmosphere were well explained by theory describing changes in the oxygen isotope composition of ecosystem water pools in response to changes in leaf transpiration and soil evaporation. 相似文献
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Long-term dynamics and community structure of freshwater gastropods exposed to parasitism and other environmental stressors 总被引:1,自引:0,他引:1
1. Freshwater communities are subject to various abrupt environmental disturbances and increasing pollution levels in their habitat. According to the nature and the periodicity of disturbances (i.e. punctuated, recurrent or continuous), one may expect different kinds of response of the target gastropod communities. 2. The gastropod community of a French lake has been investigated for 10 years to study its responses to three main environmental disturbances: supra‐seasonal droughts, recurrent proliferations of cyanobacteria and parasitism by trematodes. The relationship between this latter factor, considered as a continuous stressor, and the gastropod community was a particular focus. 3. A total of 13 280 gastropods belonging to 17 species (mostly Pulmonata with Planorbidae as the dominant family) have been sampled in the lake over the 10‐year time series. Species composition of the gastropod community varied strongly during the study period as did species richness (0–14, mean of 6.5 ± 0.4 species) and abundance of gastropods (0–4456, mean of 192 ± 72 individuals). Trematode larvae belonging to 11 morphotypes of cercariae were detected in 15 of the 17 species of gastropods and had a total prevalence of 2.9%. 4. Droughts (punctuated stressor) were responsible for the disappearance of nearly all gastropod species, and thus represent a severe environmental stressor for them. Nevertheless, the extent of this stressor was limited since the gastropod community was highly resilient. 5. Recurrent proliferations of toxic cyanobacteria (recurrent stressor) coincided with the large decline of the gastropod community, corresponding to a strong decrease in abundance and species richness. Intoxication of gastropods by toxic cyanobacteria was demonstrated by the bioaccumulation of microcystins in all gastropod tissues. 6. Trematode parasitism (continuous stressor) did not affect the gastropod community despite the possibly strong impact of parasites on some host species (those with monthly prevalence as high as 100% at some times). Indeed, abundance and species richness of gastropods were scarcely influenced by trematode prevalence or species richness. 相似文献
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CLINE CARDI ALEXANDRE VAILLANT HABY SANOU BOKARY A. KELLY JEAN‐MARC BOUVET 《Molecular ecology resources》2005,5(3):524-526
In order to study the genetic diversity and structure in the population of Vitellaria paradoxa, we characterized eight polymorphic microsatellite loci. Primers to amplify these loci were tested on 169 individual trees representing a sample of the population of shea tree in Mali. The loci were all polymorphic with a number of alleles between three to nine and with observed level of heterozygosity ranging from 0.035 to 0.507. These markers will be useful for genetic and ecological studies of this species. 相似文献
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ALEXANDRE F. SOUZA 《Austral ecology》2007,32(5):524-533
Abstract In this paper I examined the usefulness of tree population size distributions in evaluating the conservation status of populations of an endangered tree species. I set expectations derived from two complimentary views of the ecology of rainforest trees and examined whether they were met by size distributions of populations of the South American dominant conifer Araucaria angustifolia and its relationship with forest structural characteristics. Specifically, I evaluated the expectations that (i) A. angustifolia trees have larger diameter than average angiosperm trees and form a higher monospecific canopy layer above the shorter angiosperm canopies; (ii) A. angustifolia populations are characterized by size distributions with many large individuals and a long tail of relatively rare, small individuals (have symmetry coefficient <0); (iii) the symmetry of the size distribution of A. angustifolia populations is negatively related to the abundance of large (d.b.h. ≥ 10.0 cm) individuals in the population; and (iv) the abundance of A. angustifolia trees is negatively related to the abundance of angiosperm trees, as the successional accumulation of angiosperm stems would not be accompanied by the recruitment of new A. angustifolia. These expectations were evaluated using data on 25 populations of A. angustifolia sampled in the Rio Grande do Sul State in southern Brazil. The first, third and fourth expectations were met, while the second one was only partially met. This was because populations showed a bimodal distribution regarding symmetry in size distribution, with most populations showing normal or negative symmetry, and those logged, adult‐depleted populations showing positive skewness. 相似文献
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Soil carbon storage potential of direct seeding mulch-based cropping systems in the Cerrados of Brazil 总被引:1,自引:0,他引:1
MARC CORBEELS † ERIC SCOPEL † ALEXANDRE CARDOSO† MARTIAL BERNOUX‡ JEAN-MARIE DOUZET§ MARCOS SIQUEIRA NETO¶ 《Global Change Biology》2006,12(9):1773-1787
No‐tillage cropping systems with direct seeding into a mulch of plant residues from cover crops – the so‐called direct seeding mulch‐based cropping (DMC) systems – have been adopted widely over the last 10–15 years in the Cerrado region of Brazil. They are replacing the traditional soybean monoculture with bare fallow using conventional tillage (CT) practices. The objective of this study was to examine how DMC practices affect soil organic carbon (SOC) dynamics and to assess their potential for enhanced soil carbon (C) storage. The approach was to determine soil C stocks along a chronosequence of fields under DMC, and then to apply the generic decomposition and yield (G'DAY) plant–soil model to analyse the soil C storage potential for a number of cropping systems. Forty‐five fields were selected on a plateau of Ferralsols in the central Cerrado region to represent a chronosequence of 0–12 years under continuous DMC. Before DMC the fields had been under CT soybean monoculture following the clearing of the native savannah. An average increase in SOC stocks of 0.83 Mg C ha?1 yr?1 in the 0–20 cm topsoil was measured. The corresponding increase in total soil nitrogen was 79 kg N ha?1 yr?1. The G'DAY model predicted a net accumulation of 0.70–1.15 Mg C ha?1 yr?1 in the 0–40 cm topsoil for the first 12 years, depending on the type of soil and DMC system. Model predictions showed that less soil C was accumulated under DMC systems that commenced immediately after clearing the native savannah. Gains in soil C under DMC were primarily due to the introduction of a second crop that caused higher net primary productivity, leading to higher plant C inputs to soil. A rough estimation shows that the conversion of 6 million ha of CT soybean monoculture to DMC in the Cerrados would enhance soil C storage by 4.9 Tg C yr?1 during at least the first 12 years following the conversion to DMC. 相似文献
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J. BRACHET B. DE PETROCELLIS A. FICQ H. ALEXANDRE 《Differentiation; research in biological diversity》1980,17(1-3):63-76
Activation of unfertilized Chaetopterus eggs by treatment with an excess of KCl may lead to the production of unicellular ciliated larvae (Lillie's differentiation without cleavage). The effects of a number of inhibitors of protein (puromycin, cycloheximide, emetin), RNA (actinomycin D), and DNA (hydroxyurea) synthesis on differentiation without cleavage and on normal development have been studied in Chaetopterus . Incorporation of radioactive leucine, uridine, and thymine has been followed by biochemical methods and by autoradiography. The DNA content of the large polyploid nucleus has been estimated by cytophotometry. The initial pseudocleavage period of differentiation without cleavage is characterized by a burst in DNA and protein synthesis; the inhibitors have little or no effect on this burst and on pseudocleavage itself. Protein and DNA synthesis levels off during the following phase (segregation), but the inhibitors become more effective. RNA synthesis is almost linear for 20 h. These results are compared with those obtained on eggs from other species. 相似文献
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ALEXANDRE ALEIXO 《Biological journal of the Linnean Society. Linnean Society of London》2006,89(2):383-395
Phylogeographical and population genetics methods are used to reconstruct the diversification history of two species of the genus Xiphorhynchus (Aves: Dendrocolaptidae) associated with seasonally flooded forest types in Amazonia. Sequences of the mitochondrial gene cytochrome b were assessed for 21 and 30 individuals, belonging to eight and ten populations, of Xiphorhynchus kienerii and Xiphorhynchus obsoletus , respectively. Uncorrected genetic distances among unique haplotypes recovered ranged only from 0.01% to 0.4% for both species. Over 90% of the genetic variation detected in both species was partitioned within populations, and therefore was not structured geographically. Mismatch distributions and values of Tajima's D -tests indicate that both X. kienerii and X. obsoletus have had small evolutionary effective population sizes, but experienced a recent demographic expansion. These demographic expansions are tentatively dated as occurring over the last 18 000 years BP, a time frame which coincides with the establishment of the early and mid-Holocene age floodplain forest in most of central and eastern Amazonia, following a period of increased river stages throughout the basin. Based on phylogenetic, phylogeographical, and populations genetics data obtained for X. kienerii and X. obsoletus , an evolutionary scenario is proposed to account for the historical diversification of floodplain specialist species in Amazonia. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 383–395. 相似文献