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1.
Rosa Agudo Ciro Rico Carles Vilà Fernando Hiraldo José Antonio Donázar 《BMC evolutionary biology》2010,10(1):384
Background
Anthropogenic habitat modifications have led to the extinction of many species and have favoured the expansion of others. Nonetheless, the possible role of humans as a diversifying force in vertebrate evolution has rarely been considered, especially for species with long generation times. We examine the influence that humans have had on the colonization and phenotypic and genetic differentiation of an insular population of a long-lived raptor species, the Egyptian vulture (Neophron percnopterus). 相似文献2.
Maria Grcia Bozzo Enric Ribes Elena Sagrista Montserrat Poquet Mercedes Durfort 《Molecular reproduction and development》1993,34(2):206-211
We describe sperm ultrastructure and acrosome differentiation during spermiogenesis in Crassostrea gigas (Mollusca Bivalvia). The sperm cell is a uniflagellated cell of the primitive type. The head region contains a rounded or conical nucleus surmounted by small acrosome. This organelle consists of a membrane-bound acrosomal granule, the contents of which have a homogeneous density, except in the anterior region, which is positive for PTA. The acrosome also surrounds the perforatorium, which includes oriented fibrillar elements: this is the axial body. The middle piece contains four mitochondria encircling two perpendicular centrioles. The distal centriole is provided with a system of mechanical fixation to the plasma membrane, consisting of nine fibers in radial arrangement. The tail flagellum, about 50 m?m long, contains the usual microtubular axoneme. © 1993 Wiley-Liss, Inc. 相似文献
3.
Two field experiments were designed to evaluate the importance of competition, fire, repeated disturbance, and their interactions on the vegetative and reproductive performance of the Mediterranean shrub Erica multiflora over a 2.5-yr period. In a burn experiment, fire was applied to the ground-level stumps of previously clipped 13-yr-old plants with a propane torch and competition was diminished by removal of neighboring plants. Fire resulted in a reduction of sprout vigor and biomass of flowers; mature neighbors also reduced E. multiflora sprout vigor and flowering. The interaction between fire and competition was nonsignificant. In a stand burned by a wildfire we studied the effects of regenerating neighbors on target plants by removing all neighbors or only Quercus coccifera, the most dominant species in the burned stand. In this stand we also simulated herbivory by repeatedly clipping the sprouts of E. multiflora. Regenerating neighbors did not affect target plant sprout vigor after the wildfire, but did cause a decrease in the biomass of flowers per plant. Survival decreased after repeated clipping but was not affected by neighborhood treatment. The results suggest that the importance of competition on resprouting vigor was temporally variable. Variables related to plant size rather than species determined competitive superiority: resprouting neighbors did not affect resprouting performance of target plants, but mature neighbors did. In nature, fire may directly reduce vegetative and reproductive biomass by the heating effect. But it may have an indirect positive effect on biomass, by reducing competition among plants. Frequent disturbances that removed aboveground biomass of E. multiflora had a detrimental effect on target plant survival independent of neighborhood effect. 相似文献
4.
The G, Q, and C bands and the location of the nucleolar organizing regions (NORs) of the chromosomes of two male Cercopithecus neglectusare described. The diploid number of the species is 2n =62. Comparison with the karyotypes of Miopithecus talapoin (2n =54), and Erythrocebus patas (2n =54)showed the presence of total banding homeology for only 10 chromosome pairs. 相似文献
5.
In order to study the variability in nutrient concentrations in four tissues of Q. ilex in relation to soil properties, we selected fifteen stands in both Quercus ilex forests and Q. ilex-Pinus halepensis mixed forests. These stands had developed on soils derived from eight different parent materials. Three soil groups were differentiated according to their chemical properties: calcareous soils, siliceous soils, and volcanic soils. Across sites, nutrient concentrations were generally less variable in current-year tissues than in older tissues. Nitrogen and potassium showed the lowest variability among sites, their concentrations in current-year leaves ranging from 1.17% to 1.39% for N and from 0.53% to 0.68% for K. There were few statistically significant correlations between tissue element concentrations, the most frequent being the antagonistic relationship between calcium and magnesium. Nitrogen concentration in current-year leaves was negatively correlated with soil chemical fertility (nitrogen, phosphorus and potassium). This may reflect a nutritional imbalance between nitrogen and other nutrients, some of which may be more limiting than nitrogen to Q. ilex growth in Catalonia forests. Negative correlations were also found between plant magnesium and soil calcium, and positive correlations between plant calcium and soil calcium. 相似文献
6.
7.
Multiple stressors on biotic interactions: how climate change and alien species interact to affect pollination 总被引:1,自引:0,他引:1
Oliver Schweiger Jacobus C. Biesmeijer Riccardo Bommarco Thomas Hickler Philip E. Hulme Stefan Klotz Ingolf Kühn Mari Moora Anders Nielsen Ralf Ohlemüller Theodora Petanidou Simon G. Potts Petr Pyšek Jane C. Stout Martin T. Sykes Thomas Tscheulin Montserrat Vilà Gian‐Reto Walther Catrin Westphal Marten Winter Martin Zobel Josef Settele 《Biological reviews of the Cambridge Philosophical Society》2010,85(4):777-795
Global change may substantially affect biodiversity and ecosystem functioning but little is known about its effects on essential biotic interactions. Since different environmental drivers rarely act in isolation it is important to consider interactive effects. Here, we focus on how two key drivers of anthropogenic environmental change, climate change and the introduction of alien species, affect plant–pollinator interactions. Based on a literature survey we identify climatically sensitive aspects of species interactions, assess potential effects of climate change on these mechanisms, and derive hypotheses that may form the basis of future research. We find that both climate change and alien species will ultimately lead to the creation of novel communities. In these communities certain interactions may no longer occur while there will also be potential for the emergence of new relationships. Alien species can both partly compensate for the often negative effects of climate change but also amplify them in some cases. Since potential positive effects are often restricted to generalist interactions among species, climate change and alien species in combination can result in significant threats to more specialist interactions involving native species. 相似文献
8.
Emili Saló Ana Maria Muñoz-Mármol José Ramon Bayascas-Ramirez Jordi Garcia-Fernàndez Agusti Miralles Andreu Casali Montserrat Corominas Jaume Baguñá 《Hydrobiologia》1995,305(1-3):269-275
To identify potential pattern control and cell determination and/or differentiation genes in the freshwater planarian Dugesial (G.) tigrina, we searched for homeobox genes of different types in the genome of this primitive metazoan. We applied two basic approaches: 1) Screening the cDNA library with degenerate oligonucleotides corresponding to the most conserved amino acid sequence from helix-3 of the homeodomain of each family; and 2) PCR amplification of genomic DNA or cDNA, using two sets of degenerated oligonucleotides corresponding to helices 1 and 3 of the homeodomain or two specific domains of the POU family. Using the first strategy we have identified and characterized two tissue-specific cell determination and/or differentiation NK-type homeobox genes. Using the second strategy we have identified several homeobox genes that belong to the HOM/Hox, paired (prd) or POU families. 相似文献
9.
Pla M La Paz JL Peñas G García N Palaudelmàs M Esteve T Messeguer J Melé E 《Transgenic research》2006,15(2):219-228
Maize is one of the main crops worldwide and an increasing number of genetically modified (GM) maize varieties are cultivated
and commercialized in many countries in parallel to conventional crops. Given the labeling rules established e.g. in the European
Union and the necessary coexistence between GM and non-GM crops, it is important to determine the extent of pollen dissemination
from transgenic maize to other cultivars under field conditions. The most widely used methods for quantitative detection of
GMO are based on real-time PCR, which implies the results are expressed in genome percentages (in contrast to seed or grain
percentages). Our objective was to assess the accuracy of real-time PCR based assays to accurately quantify the contents of
transgenic grains in non-GM fields in comparison with the real cross-fertilization rate as determined by phenotypical analysis.
We performed this study in a region where both GM and conventional maize are normally cultivated and used the predominant
transgenic maize Mon810 in combination with a conventional maize variety which displays the characteristic of white grains
(therefore allowing cross-pollination quantification as percentage of yellow grains). Our results indicated an excellent correlation
between real-time PCR results and number of cross-fertilized grains at Mon810 levels of 0.1–10%. In contrast, Mon810 percentage
estimated by weight of grains produced less accurate results. Finally, we present and discuss the pattern of pollen-mediated
gene flow from GM to conventional maize in an example case under field conditions. 相似文献
10.