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1.
In monospecific stands of Acacia drepanolobium in Laikipia, Kenya, virtually all but the smallest trees are occupied by one of four species of ants. Although trees are
a limiting resource, all four ant species are maintained in this system. Three separate lines of evidence confirm a linear
dominance hierarchy among these four ants: (1) experimentally staged conflicts, (2) natural transitions among 1773 tagged
trees over a 6-month period, and (3) the average sizes of trees occupied by ants of different species. Short-term dynamics
during a drying period reveal that many smaller trees (<1 m) occupied by dominant ants were subsequently abandoned, and that
abandoned trees had grown more slowly than those that were not abandoned. Height growth increments over 6 months were generally
independent of ant occupant, but increased with tree height. Among taller trees (>1 m), changes in ant occupation congruent
with the dominance hierarchy (i.e., transitions from more subordinate ant species to more dominant ant species) occurred on
trees that grew faster than average. In contrast, the (less frequent) changes in ant occupation ”against” the direction of
the dominance hierarchy occurred on trees that grew more slowly than average. Observed correlations between tree vigor and
takeover direction suggest that colony growth of dominant ant species is either favored in more productive microhabitats,
or that such colonies differentially seek out healthier trees for conquest. Colonies of dominant species may differentially
abandon more slowly growing trees during (dry) periods of retrenchment, or suffer higher mortality on these trees. Subordinate
ant species appear to move onto these abandoned trees and, to a lesser extent, colonize new recruits in the sapling class.
These data reveal that within a simple linear dominance hierarchy, short-term variations exist that may reveal underlying
mechanisms associated with coexistence.
Received: 24 June 1999 / Accepted: 3 December 1999 相似文献
2.
In Macaranga myrmecophytes, differences in the production of the food bodies (FBs), on which symbiont ants feed, may relate to the intensity
of antiherbivore defense by the ants. Interspecific comparisons among Macaranga species on such a mutualistic cost give important information on their strategies and evolution of antiherbivore defense.
In this study, the carbon and nitrogen contents of FBs as well as the production rate of FBs were measured in three Macaranga species, M. winkleri, M. trachyphylla, and M. beccariana. There were significant differences in the production rates of FBs among species; the investment in FBs was greater in the
Macaranga species in which ant defenses were more intensive. The carbon and nitrogen contents of FBs were significantly different among
the three species, although they did not match the intensity of ant defense; the nitrogen content, especially, was greatest
in the species of least intensive ant defense. It is suggested that Macaranga plants may have differentiated in the dependence on ant defense by controlling the total amount of nitrogen of FBs, not simply
by nitrogen content.
Received: January 19, 2001 / Accepted: December 23, 2001 相似文献
3.
P. A. Butcher G. F. Moran R. Bell 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2000,100(3-4):576-583
Random genomic probes were used to assess levels of restriction fragment length polymorphism (RFLP) in two 2-generation outbred
pedigrees of Acacia mangium Willd. Probes were evaluated for their ability to detect polymorphic loci in each pedigree and to determine the relative
efficiency of different restriction enzymes in revealing polymorphisms. Sixty two percent of the probes which detected single-
or low-copy number sequences revealed polymorphisms with at least one restriction enyzme. HpaII was the most efficient in detecting polymorphism among first-generation individuals. The recognition sequence of HpaII contains a CpG dimer, suggesting that cytosines in the CpG sequence may be hotspots for mutation in plant genomes, as previously
reported in bacterial and mammalian genomes. Mendelian inheritance of 230 loci was demonstrated based on single-locus segregation
in second-generation individuals. Less than 5% of loci showed evidence of segregation distortion. The proportion of fully
informative loci (15%) was lower than previously reported in eucalypts reflecting the lower level of genetic diversity in
A. mangium. The RFLP probes are suitable for the construction of a high-density genetic linkage map in A. mangium. Cross-hybridisation of the A.mangium RFLPs to DNA from species representing the three subgenera of the genus Acacia indicates that these markers could be used in breeding programs of other diploid acacias, for comparative studies of genome
organisation, and for phylogenetic studies.
Received: 5. June 1999 / Accepted: 30 July 1999 相似文献
4.
Sequence-related amplified polymorphism (SRAP), a new marker system based on a simple PCR reaction: its application to mapping and gene tagging in Brassica 总被引:187,自引:0,他引:187
G. Li C. F. Quiros 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2001,103(2-3):455-461
We developed a simple marker technique called sequence-related amplified polymorphism (SRAP) aimed for the amplification of
open reading frames (ORFs). It is based on two-primer amplification. The primers are 17 or 18 nucleotides long and consist
of the following elements. Core sequences, which are 13 to 14 bases long, where the first 10 or 11 bases starting at the 5′
end, are sequences of no specific constitution (”filler” sequences), followed by the sequence CCGG in the forward primer and
AATT in the reverse primer. The core is followed by three selective nucleotides at the 3′ end. The filler sequences of the
forward and reverse primers must be different from each other and can be 10 or 11 bases long. For the first five cycles the
annealing temperature is set at 35°C. The following 35 cycles are run at 50°C. The amplified DNA fragments are separated by
denaturing acrylamide gels and detected by autoradiography. We tested the marker technique in a series of recombinant inbred
and doubled-haploid lines of Brassica oleracea L. After sequencing, approximately 45% of the gel-isolated bands matched known genes in the Genbank database. Twenty percent
of the SRAP markers were co-dominant, which was demonstrated by sequencing. Construction of a linkage map revealed an even
distribution of the SRAP markers in nine major linkage groups, not differing in this regard to AFLP markers. We successfully
tagged the glucosinolate desaturation gene BoGLS-ALK with these markers. SRAPs were also easily amplified in other crops such as potato, rice, lettuce, Chinese cabbage (Brassica rapa L.), rapeseed (Brassica napus L.), garlic, apple, citrus, and celery. We also amplified cDNA isolated from different tissues of Chinese cabbage, allowing the fingerprinting of these sequences.
Received: 3 November 2000 / Accepted 24 November 2000 相似文献
5.
Estimation of fine root mortality and growth from simple measurements: a method based on system dynamics 总被引:3,自引:0,他引:3
This study is a further development of a dynamic compartment-flow analysis, intended as an analytical tool for the empirical
estimation of fine root growth, mortality and decomposition in forest soil. General properties of the dynamic system are utilised
to interpret relatively simple measurements of standing biomass, necromass, and decomposition, in order to derive estimates
of the process rates. The method is based on the finding that the ratio of fine root necromass to biomass is related to the
specific rates of decomposition, mortality, and net growth. If the decomposition rate is measured and the net growth trend
is determined from live root measurements, mortality and gross growth can be estimated using these relationships, provided
certain regularity requirements are met. These requirements are explicated, such that the estimates can be easily assessed
for reliability. To illustrate the use of the method, it was applied to the estimation of specific mortality rates in seven
Scots pine stands of different ages and site types. A reanalysis of a previous sequential coring study yielded consistent
results. The advantage of this method is that, unlike the standard analysis of sequential cores, it accounts for the possibility
of simultaneous growth, mortality and decomposition. It is therefore applicable to situations with no apparent fluctuations
or trend in the biomass and necromass levels. No minimum sampling interval is required; hence the method also allows for more
extensive or prolonged studies.
Received: 1 June 1999 / Accepted: 20 January 2000 相似文献
6.
Plants growing on an environmentally stressed glacier forefront on soil low in N and organic matter have abundant root colonizations
by dark-septate fungi. As the plants appeared fit for this severe habitat, it was hypothesized that the dark-septate endophytes
were neutral or beneficial rather than detrimental to the plants. To test this hypothesis, we designed a growth-room experiment
with Pinus contorta grown on forefront soil inoculated with the dark-septate fungus Phialocephala fortinii in the absence of climatic stress. N and organic matter treatments were included to explore their interaction with the fungal
inoculation. P. fortinii colonized roots inter- and intracellularly and occasionally formed microsclerotia. Inoculated plants absorbed significantly
more P than noninoculated plants in all combinations of N and organic matter. Without added N, neither inoculation nor organic
matter addition improved plant growth or N uptake, showing that N indeed limits plant growth in this substrate. With added
N, however, both organic matter addition and inoculation significantly increased total pine biomass and N uptake. The enhanced
P uptake by the P. fortinii-inoculated pine as well as the increased pine growth and N uptake in the treatment combining P. fortinii and N appear as typical mycorrhizal responses.
Accepted: 20 October 1997 相似文献
7.
Alan Birkett 《African Journal of Ecology》2002,40(3):276-282
The habitat in an enclosed black rhino sanctuary, the Sweetwaters Game Reserve in Kenya, is being altered as populations of elephant, giraffe and black rhino increase. Height‐specific browse impact data were recorded for 1075 trees of the dominant species, the whistling thorn, Acacia drepanolobium. Rhinos and elephants browsed 18% of these trees in 1 year, including 5% that were killed or removed. The remaining trees were subjected to high levels of giraffe browse and low rainfall and grew by only 7.5 cm in a year. A mathematical model has been constructed that predicts how the number of trees ha?1 will change with time under different browsing impacts. The model compares recruitment rate with removal rate and estimates that the number of trees ha?1 will fall by 2% per year under the current browsing impact of black rhino (0.27 per km2), elephant (1.1 per km2) and giraffe (1.9 per km2). In 7 years, if the rhino and elephant populations continue to increase at the current rates, tree density will be falling by 5% per year and nearly one‐third of the trees will have been removed. These conditions are unsustainable and will result in habitat change and may affect rhino breeding. Several ways of alleviating the problem are discussed. 相似文献
8.
Micky D. Eubanks Kimberly A. Nesci Mette K. Petersen Zhiwei Liu Horacio Bonfil Sanchez 《Oecologia》1997,109(3):454-460
Larvae of a Polyhymno species (Lepidoptera: Gelechiidae) feed on the ant-defended acacia, Acacia cornigera, in the tropical lowlands of Veracruz, Mexico. Polyhymno larvae construct sealed shelters by silking together the pinna or pinnules of acacia leaves. Although larval density and
larval survival are higher on acacias not occupied by ants, shelters serve as a partial refuge from the ant Pseudomyrmex ferruginea (Hymenoptera: Formicidae), which defends A. cornigera plants; thus, shelters provide Polyhymno larvae access to an ant-defended host plant. P. ferruginea ants act as the primary antiherbivore defense of A. cornigera plants, which lack the chemical and mechanical defenses of non-ant-defended acacias. Thus, defeating the ant defense of A. cornigera provides Polyhymno larvae access to an otherwise poorly defended host plant. Damage caused by Polyhymno larval feeding reaches levels which can kill A. cornigera plants.
Received: 6 June 1996 / Accepted: 6 September 1996 相似文献
9.
We report the effect of ectomycorrhizal fungi (Suillus variegatus, Paxillus involutus) and defoliation on polyamine concentrations in pine (Pinus silvestris) and birch (Betula pendula) foliage and roots. Symbiotic root tips showed consistently higher concentrations of putrescine than non-symbiotic roots.
Partial defoliation had no effect on the polyamine levels in mycorrhizal pine or birch roots. The foliage of mycorrhizal pine
seedlings had lower putrescine concentrations and higher spermidine than foliage of non-mycorrhizal plants, and defoliation
reversed this pattern. The response to partial defoliation differed in birch foliage: mycorrhizal status had no effect and
all new growth after defoliation had higher spermidine levels than in non-defoliated birch. The potential role of polyamines
in mycorrhizal symbiosis is discussed.
Accepted: 26 February 1997 相似文献
10.
Although the significance of canopy plant communities to ecosystem function is well documented, the process by which such
communities become established in trees remains poorly known. Colonization of tree surfaces by canopy-dwelling plants often
begins with the establishment of bryophytes, so the conditions that affect the dispersal of bryophytes in the forest canopy
merit study. We assessed success rates of one mechanism of bryophyte propagation, the aerial dispersal of macroscopic fragments,
using an experimental approach. We quantified interception and retention of marked fragments released from a 36 cm×36 cm grid
50 cm above branches of saplings and mature trees of the species Ocotea tonduzii in a montane cloud forest in Costa Rica. Only 1% of bryophyte fragments dropped over sapling crowns in this manner were retained
for the 6-month duration of the study, while branches in the forest canopy with intact epiphyte loads and branches that had
been stripped of their epiphytes retained 24% and 5%, respectively. Our results suggest that larger-diameter branches and
the presence of other epiphytes can both improve the retention of bryophyte fragments on canopy branches. Further work will
be needed to address the relative roles of other dispersal mechanisms (spores, gemmae, microscopic bryophyte fragments) and
the dynamics of growth and establishment of macroscopic bryophyte fragments following their interception.
Received: 1 March 1999 / Accepted: 24 August 1999 相似文献
11.
Identification of DNA amplification fingerprinting (DAF) markers close to the symbiosis-ineffective sym31 mutation of pea (Pisum sativum L.) 总被引:1,自引:0,他引:1
A. E. Men A. Y. Borisov S. M. Rozov K. V. Ushakov V. E. Tsyganov I. A. Tikhonovich P. M. Gresshoff 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1999,98(6-7):929-936
We demonstrate efficient genome mapping through a combination of bulked segregant analysis (BSA) with DNA amplification fingerprinting
(DAF). Two sets of 64 octamer DAF primers, along with two PCR programs of low- and high-annealing temperatures (30°C and 55°C,
respectively), appeared to be enough to locate molecular markers within 2–5 cM of a gene of interest. This approach allowed
the rapid identification of four BSA markers linked to the pea (Pisum sativum L.) Sym31 gene, which is responsible for bacteroid and symbiosome differentiation. Three of these markers are shown to be tightly linked
to the sym31 mutation. Two markers flanking the Sym31 gene, A21-310 and B1-277, cover a 4–5 cM interval of pea linkage group 3. Both markers were converted to sequence-characterized
amplified regions (SCARs). The flanking markers may be potential tools for marker-assisted selection or for positional cloning
of the Sym31 gene.
Received: 2 July 1998 / Accepted: 8 October 1998 相似文献
12.
Mutualisms involve the exchange of resources and these resources attract exploiters and predators. Because predators may have a stronger effect either on mutualists or on exploiters, their net effect on the mutualism may be positive or negative. Ants and Ficus -associated wasps are a potential example. These wasps could represent sufficient food to ensure a permanent presence of predators. If this is the case then we may expect divergent selection (dependent on fig species) on traits facilitating or impeding ant predatory activity. Dioecious Ficus species in Brunei present the opportunity to determine whether presence of fig wasps on a tree ensures increased presence of ants because: (1) wasps are mainly present on male trees, thus allowing study of the effect of wasp abundance on ant presence; and (2) preliminary observations showed that ants present on trees were mainly predatory species that do not tend hemipterans. We show here, for several dioecious Ficus species, that many more ants were present on male trees than on female trees. Furthermore, these ants were mainly dominant predatory taxa that often nested in the male trees. Hence, wasps on male trees provide a sufficient resource in terms of quantity and reliability to ensure the continuous presence of dominant ants on the trees. 相似文献
13.
Workers of three ant species (Lasius niger, Lasius flavus, Myrmica rubra) were caged in the laboratory together with caterpillars and pupae of five species of lycaenid butterflies. Mortality of ants was 3–5 times higher when the ants were confined with larvae lacking a dorsal nectar organ (Lycaena phlaeas, Lycaena tityrus) rather than with caterpillars which possess a nectar gland (Aricia agestis, Polyommatus bellargus, P. icarus). For all five species, ant survival was always lower at the pupal stage (where a nectar organ is always absent) than at the caterpillar stage and was largely equivalent for the butterfly species tested. The experimental data confirm earlier estimates that ants can derive nutritive benefits from tending facultatively myrmecophilous lycaenid caterpillars, even though these caterpillars produce nectarlike secretions at low rates. 相似文献
14.
G. A. Akpan 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2000,100(2):315-318
Cytogenetic characteristics confirm that Hibiscus acetosella and Hibiscus cannabinus are outbreeders, while Hibiscus asper, Hibiscus physaloides, Hibiscus sabdariffa and Hibiscus surattensis have evolved into inbreeders. The inbreeding species appear to have co-evolved a floral structure in which some anthers abut
on the stigma prior to anthesis.
Received: 19 February 1999 / Accepted: 17 June 1999 相似文献
15.
Flow cytometric analysis of the chromosomes and stability of a wheat cell-culture line 总被引:3,自引:0,他引:3
T. Schwarzacher M. L. Wang A. R. Leitch G. Moore J. S. Heslop-Harrison N. Miller 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(1):91-97
A rapidly growing, long-term suspension culture derived from Triticum aestivum L. (wheat) was synchronized using hydroxyurea and colchicine, and a chromosome suspension with chromosomes was made. After staining with the DNA-specific fluorochromes Hoechst 33258 and Chromomycin univariate and bivariate flow-cytometry histograms showed 15 clearly resolved peaks corresponding to individual chromosome
types or groups of chromosomes with similar DNA contents. The flow karyotype was closely similar to a histogram of DNA content
measurements of Feulgen-stained chromosomes made by microdensitometry. We were able to show the stability of the flow karyotype
of the cell line over a year, while a parallel subculture had a slightly different, stable, karyotype following different
growth conditions. The data indicate that flow cytometric analysis of plant karyotypes enables accurate, statistically precise
chromosome classification and karyotyping of cereals. There was little overlap between individual flow-histogram peaks, so
the method is useful for flow sorting and the construction of chromosome specific-recombinant DNA libraries. Using bivariate
analysis, the AT:GC ratio of all the chromosomes was remarkably similar, in striking contrast to mammalian flow karyotypes.
We speculate about a fundamental difference in organization and homogenization of DNA sequences between chromosomes within
mammalian and plant genomes.
Received: 24 April 1996 / Accepted: 24 May 1996 相似文献
16.
Induction of apoptosis by cooperative bacteria in the morphogenesis of host epithelial tissues 总被引:9,自引:0,他引:9
Associations with pathogenic bacteria have recently been shown to initiate apoptotic programs in the cells of their animal
hosts, where host cell death is hypothesized to be a response of the immune system, either initiated as a mechanism of host
defense or bacterial offense. In this study, we present evidence that bacterial initiation of apoptosis is neither restricted
to pathogenesis nor to the initation of an immune response. In the cooperative association between the sepiolid squid Euprymna scolopes and the luminous bacterium Vibrio fischeri, the bacteria induce a dramatic morphogenesis of the host tissues during the first few days of interaction between these
partners. The most striking change is the bacteria-triggered loss of an extensive superficial epithelium that potentiates
the infection process. Our analyses of these tissues revealed that the bacteria induce apoptosis in the cells that comprise
this epithelium within hours of the interaction with bacteria. Ultrastructural analysis revealed that after 24 h the integrity
of the epithelium had been lost, i.e., the basement membrane had degenerated and the majority of the cells exhibited signs
of apoptosis, most notably chromatin condensation. Analysis of these tissues with probes that reveal intracellular acidification
showed that the cells first undergo an initial acidification beginning about 6–8 h after exposure to V. fischeri. As determined by end-labeling of DNA fragments, extensive endonuclease activity was detected at approximately 16–20 h post-infection.
These data provide evidence that cooperative bacteria can participate in the remodeling of host tissues through the induction
of host apoptotic programs.
Received: 10 November 1997 / Accepted: 22 April 1998 相似文献
17.
Melnikov analysis of chaos in a simple epidemiological model 总被引:4,自引:0,他引:4
Melnikov’s method is applied to an SIR model of epidemic dynamics with a periodically modulated nonlinear incidence rate.
This analysis establishes mathematically, for the first time, the existence of chaotic motion in these models. A related technique
also makes it possible to prove that homoclinic bifurcations occurs in the model.
Received 8 August 1995; received in revised form 21 November 1995 相似文献
18.
Tsuji LJ DeIuliis G Hansell RI Kozlovic DR Sokolowski MB 《International journal of biometeorology》2000,44(3):134-140
This paper is the first to integrate both field and theoretical approaches to demonstrate that fertility benefits can be a
direct benefit to females mating on the classical lek. Field data collected for male sharp-tailed grouse (Tympanuchus phasianellus), a classical lekking species, revealed potential fertility benefits for selective females. Adult males and individuals occupying
centrally located territories on the lek were found to have significantly larger testes than juveniles and peripheral individuals.
Further, using empirical data from previously published studies of classical lekking grouse species, time-series analysis
was employed to illustrate that female mating patterns, seasonal and daily, were non-random. We are the first to show that
these patterns coincide with times when male fertility is at its peak.
Received: 26 February 1999 / Revised: 13 December 1999 / Accepted: 15 March 2000 相似文献
19.
This study quantified intersite variation and spatial pattern in arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) infectivity
of soils among six sites constituting a successional chronosequence in southwestern Ohio, USA. The study sites included an
active agricultural field (chronic disturbance), a site which had been stripped of its surface soil (pseudo-stripmine, acute
disturbance), 5- and 10-year-old fields, a 25- to 30-year-old prairie restoration, and an undisturbed, mature forest. AM infectivity
was lower in the agricultural field, successional fields, and prairie than in the mature forest, but there was no clear correlation
between time since disturbance and the overall level of AM infectivity. Spatial structure in AM infectivity decreased with
time since disturbance. In the pseudo-stripmine site and active soybean field, semivariance analysis attributed 44–50% of
the total variance in AM infectivity among samples to spatial structure, whereas spatial dependancy accounted for only 18%
of total variance in the mature forest. Kriging of AM infectiveness demonstrated small, isolated areas in the disturbed plots
that were devoid of AM infectiveness, whereas the kriged AM maps of the other four sites showed AM infectiveness to become
progressively more homogeneous. ECM infectiveness was lacking from 35–50% of the samples from the disturbed sites, and both
overall ECM infectiveness and ECM diversity increased with time since disturbance. Approximately 44% of the variance in ECM
infectiveness was related to spatial structure in the two disturbed sites, and large areas entirely devoid of ECM infectivity
were present on the kriged ECM maps for these sites. There was less spatial structure in ECM in the old fields and prairie
and very little in the mature forest. The results of this study emphasize the need to explicitly evaluate spatial heterogeneity
in mycorrhizal infectivity in studies of the role of mycorrhizae in succession.
Accepted: 4 August 1995 相似文献
20.
L. Muscatine C. Ferrier-Pagès A. Blackburn R. D. Gates G. Baghdasarian D. Allemand 《Coral reefs (Online)》1998,17(4):329-337
Symbiotic dinoflagellates are abundant in the endoderm cells of tropical marine anthozoans, but the cell-specific density
(CSD) of symbionts has not yet been investigated. In this study we used mechanical and enzymatic methods of maceration, and
staining with substrate-specific fluorochromes, to observe a large number of individual host cells from 33 species of tropical
anthozoans collected in Florida, Hawaii and Jamaica or cultured in Monaco. In the majority of species, most of the host cells
contained a single algal cell (singlet). Host cells with two or more (up to six) algae were much less abundant. The average
CSD for the 33 species was 1.54±0.30 (range 1.11 to 2.19). Singlets arranged in a monolayer can account for the areal density
of algae observed in many anthozoans. The dinoflagellates occupy most of the interior of macerated host cells, leaving the
host cytoplasm and cell membrane as a thin outer layer, often unresolvable by light microscopy. This spatial arrangement may
favor diffusion and transport of CO2, bicarbonate ions, and nutrients from the environment to the algae. The effect of nutrient enrichment on CSD was determined
by exposing eleven species to chronically elevated levels of ammonium-N. After four weeks all species exhibited a dramatic
increase in algal mitotic index and CSD. The potential consequences of environmentally induced increases in CSD in tropical
anthozoans are discussed in terms of the decreased cell-specific photosynthesis (CO2 limitation) and decreased rates of calcification observed in other studies.
Accepted: 16 February 1998 相似文献