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1.
2.
The tradeoff between colonization and competitive ability has been proposed as a mechanism for ecological succession, and this tradeoff has been demonstrated in multiple successional communities. The tradeoff between competitive ability and predation resistance is also a widely-described phenomenon; however, this tradeoff is not usually postulated as a cause of ecological succession. Early successional species that arrive before predator colonization could be either (1) less vulnerable to predation than their successors, by virtue of being poor competitors (direct competition-predation tradeoff); or (2) equally or more vulnerable to predation, because they normally colonize ahead of predators in succession and therefore are not evolutionarily adapted to avoid predators that they rarely encounter (no competition–predation tradeoff). To test these alternative hypotheses, we established water-filled containers in an oak–hickory forest. We allowed half of the containers to be naturally colonized by early-successional Culex mosquitoes, mid-successional Aedes mosquitoes, and the mosquito predator Toxorhynchites rutilus. In the other half of the containers, we prevented Aedes colonization via systematic removal of Aedes eggs, but allowed Culex and T. rutilus to colonize. The numbers of mature Culex larvae and pupae, and later the total number of Culex, were significantly greater in containers where Aedes had been removed, which suggests that Culex are competitively suppressed by Aedes. Toxorhynchites rutilus abundance and colonization rate were unaffected by the removal of Aedes, and densities of both Culex and Aedes decreased significantly with T. rutilus abundance in both treatments. In-laboratory bioassays showed that Culex were significantly more vulnerable to predation by T. rutilus than were Aedes. These data are consistent with the hypothesis that Culex and Aedes demonstrate a direct colonization–competition tradeoff, and are inconsistent with the hypothesis of a direct competition–predation tradeoff. 相似文献
3.
Andrew C. Stainthorpe J. Colin Murrell George P. C. Salmond Howard Dalton Veronica Lees 《Archives of microbiology》1989,152(2):154-159
Methane monooxygenase (MMO) is the enzyme responsible for the conversion of methane to methanol in methanotrophic bacteria. In addition, this enzyme complex oxidizes a wide range of aliphatic and aromatic compounds in a number of potentially useful biotransformations. In this study, we have used biochemical data obtained from purification and characterization of the soluble MMO from Methylococcus capsulatus (Bath), to identify structural genes encoding this enzyme by oligonucleotide probing. The genes encoding the and subunits of MMO were found to be chromosomally located and were linked in this organism. We report here on the analysis of a recombinant plasmid containing 12 kilobases of Methylococcus DNA and provide the first evidence for the localization and linkage of genes encoding the methane monooxygenase enzyme complex. DNA sequence analysis suggests that the primary structures of the and subunit of MMO are completely novel and the complete sequence of these genes is presented. 相似文献
4.
NAD+-dependent propan-1-ol and propan-2-ol dehydrogenase activities were detected in cell-free extracts of Rhodococcus rhodochrous PNKb1 grown on propane and potential intermediates of propane oxidation. However, it was unclear whether this activity was mediated by one or more enzymes. The isolation of mutants unable to utilize propan-1-ol (alcA-) or propan-2-ol (alcB-) as sole carbon and energy sources demonstrated that these substrates are metabolized by different alcohol dehydrogenases. These mutants were also unable to utilize propane as a growth substrate indicating that both alcohols are intermediates of propane metabolism. Therefore, propane is metabolized by terminal and sub-terminal oxidation pathways. Westernblot analysis demonstrated that a previously purified NAD+-dependent propan-2-ol dehydrogenase (Ashraf and Murrell 1990) was only synthesized after growth on propane and sub-terminal oxidation intermediates (but not acetone), and not propan-1-ol or terminal oxidation intermediates. Therefore, our evidence suggest that another dehydrogenase is involved in the metabolism of propan-1-ol and this agrees with the isolation of the alcA- and alcB- phenotypes. The previously characterized NAD+-dependent propan-2-ol dehydrogenase from R. rhodochrous PNKb1 is highly conserved amongst members of the propane-utilizing Rhodococcus-Nocardia complex. 相似文献
5.
We examined the effect of interacting dipicolinic acid and its calcium chelate on the wet and dry density of DNA. Complexes are produced whose densities are different from those of the individual components. Also, we observed two modes of binding, one strong the other weak, between DPA or CaDPA and DNA. The strength of the binding modes was reflected in the rate of dissolution of the complexes as monitored by changes in wet density with time and temperature. We conclude from these and other data in the literature that the interaction of dipicolinic acid with DNA not only influences the spore wet density and the ratio of core/core+ cortex volume, but may also influence the spore heat resistance. 相似文献
6.
Samples of tongue or diaphragm from 2,056 black bears harvested in Pennsylvania during the 1981-1983 hunting seasons were examined for larvae of Trichinella spiralis by peptic digestion. Sixteen males and 21 females were infected. The overall prevalence of infection was 1.8%. Infected animals were distributed widely throughout the range of the bear in Pennsylvania. In samples from infected bears, the geometric mean density of muscle larvae was 7.8 per g of tissue (LPG). There were neither sex- nor age-related differences in prevalence or intensity of infection. Virtually all bears harvested in Pennsylvania are consumed as food, which often is shared widely among hunters, their friends and relatives. Furthermore, high densities of larvae occurred in some bears (i.e., 300, 348, 465, 512, 555, and 912 LPG). Thus, a basis for potential, single-source outbreaks of severe human trichinosis exists. 相似文献
7.
Isolation and characterization of a large,neurite-associated glycoconjugate from neuroblastoma cells
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A high molecular weight glycoconjugate has been isolated from neurite-producing neuronal tumor cells in culture and has been designated as I(0) based on its elution characteristics in gel filtration chromatography. This molecule cannot be found in a variety of nonneuronal cells. I(0) is found in the substratum-attached material or cell fraction of neurite-producing neuroblastoma cells, depending upon culture conditions. It is found in the substratum-bound fraction of B104 rat neuroblastoma cells during serum starvation and in the EGTA-detached cell fraction of B104 cells grown in chemically defined N2 medium. It occurs only in the cell fraction of the human neuroblastoma line Platt. Examination of behavioral variants of the B104 rat line further strengthens the association of I(0) with neurite production; the constitutive neurite-producing E(R)B9 variant contains I(0) while the non-neurite-producing E(R)A11 variant does not. I(0) is large, eluting in the void volume of sepharose-CL2B columns. Radioiodination of intact cells with lactoperoxidase shows I(0) to be a cell surface component. Metabolic radiolabeling studies show that it contains a high proportion of polysaccharide to protein, does not contain mannose, and is unsulfated. Alkaline borohydride reduction release two size classes of large polysaccharide chain. The alkaline reduction results, along with the mannose incorporation studies, show the presence of O-glycosidic linkages and few, if any, N-linkages. Resistance to nitrous acid deamination, insensitivity to glycosaminoglycan lyases, and the absence of sulfation, indicate that I(0) does not contain the glycosaminoglycans hyaluronic acid, chondroitin-, dermatan-, or heparin- sulfates. Affinity column chromatography reveals high binding affinity of I(0) to polyornithine and no binding to gelatin (collagen) or the glycosaminoglycans hyaluronate and heparin. These studies describe a unique high molecular weight glycoconjugate on the surface of neurite-producing neuroblastoma cell lines from two species. 相似文献
8.
Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal 总被引:10,自引:9,他引:1
We have developed a new approach to the measurement of phylogenetic signal
in character state matrices called relative apparent synapomorphy analysis
(RASA). RASA provides a deterministic, statistical measure of natural
cladistic hierarchy (phylogenetic signal) in character state matrices. The
method works by determining whether a measure of the rate of increase of
cladistic similarity among pairs of taxa as a function of phenetic
similarity is greater than a null equiprobable rate of increase. Our
investigation of the utility and limitations of RASA using simulated and
bacteriophage T7 data sets indicates that the method has numerous
advantages over existing measures of signal. A first advantage is
computational efficiency. A second advantage is that RASA employs known
methods of statistical inference, providing measurable sensitivity and
power. The performance of RASA is examined under various conditions of
branching evolution as the number of characters, character states per
character, and mutations per branch length are varied. RASA appears to
provide an unbiased and reliable measure of phylogenetic signal, and the
general approach promises to be useful in the development of new techniques
that should increase the rigor and reliability of phylogenetic estimates.
相似文献
9.
Bouwe R. Reijenga Benjamin G. Freeman David J. Murrell Alex L. Pigot 《Global Ecology and Biogeography》2023,32(10):1748-1759
Aim
The exceptional turnover in biota with elevation and number of species coexisting at any elevation makes tropical mountains hotspots of biodiversity. However, understanding the historical processes through which species arising in geographical isolation (i.e. allopatry) assemble along the same mountain slope (i.e. sympatry) remains a major challenge. Multiple models have been proposed including (1) the sorting of already elevationally divergent species, (2) the displacement of elevation upon secondary contact, potentially followed by convergence, or (3) elevational conservatism, in which ancestral elevational ranges are retained. However, the relative contribution of these processes to generating patterns of elevational overlap and turnover is unknown.Location
Tropical mountains of Central- and South-America.Time Period
The last 12 myr.Major Taxa Studied
Birds.Methods
We collate a dataset of 165 avian sister pairs containing estimates of phylogenetic age, geographical and regional elevational range overlap. We develop a framework based on continuous-time Markov models to infer the relative frequency of different historical pathways in explaining present-day overlap and turnover of sympatric species along elevational gradients.Results
We show that turnover of closely related bird species across elevation can predominantly be explained by displacement of elevation ranges upon contact (81%) rather than elevational divergence in allopatry (19%). In contrast, overlap along elevation gradients is primarily (88%) explained by conservatism of elevational ranges rather than displacement followed by elevational expansion (12%).Main Conclusions
Bird communities across elevation gradients are assembled through a mix of processes, including the sorting, displacement and conservatism of species elevation ranges. The dominant role of conservatism in explaining co-occurrence of species on mountain slopes rejects more complex scenarios requiring displacement followed by expansion. The ability of closely related species to coexist without elevational divergence provides a direct and faster pathway to sympatry and helps explain the exceptional species richness of tropical mountains. 相似文献10.
Molecular evolution of voltage-sensitive ion channel genes: on the origins of electrical excitability 总被引:14,自引:0,他引:14
We have analyzed nucleic acid and amino acid sequence alignments of a
variety of voltage-sensitive ion channels, using several methods for
phylogenetic tree reconstruction. Ancient duplications within this family
gave rise to three distantly related groups, one consisting of the Na+ and
Ca++ channels, another the K+ channels, and a third including the cyclic
nucleotide-binding channels. A series of gene duplications produced at
least seven mammalian homologues of the Drosophila Shaker K+ channel;
clones of only three of these genes are available from all three mammalian
species examined (mouse, rat, and human), pointing to specific genes that
have yet to be recovered in one or another of these species. The
Shaw-related K+ channels and the Na+ channel family have also undergone
considerable expansion in mammals, relative to flies. These expansions
presumably reflect the needs of the high degree of physiological and
neuronal complexity of mammals. Analysis of the separate domains of the
four-domain channels (Ca++ and Na+) supports their having evolved by two
sequential gene duplications and implies the historical existence of a
functional two-domain channel.
相似文献