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排序方式: 共有100条查询结果,搜索用时 11 毫秒
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2.
Divergence in cuticular hydrocarbons between parapatric subspecies of the meadow grasshopper, Chorthippus parallelus (Orthoptera, Acrididae) 总被引:1,自引:0,他引:1
RACHEL M. NEEMS ROGER K. BUTLIN 《Biological journal of the Linnean Society. Linnean Society of London》1995,54(2):139-149
Two subspecies of the grasshopper Chorthippus parallelus (Orthoptera; Acrididae) meet and form a hybrid zone in the Pyrenees. Here we investigate whether the subspecies differ in the blend of cuticular hydrocarbons. Such differences may function as chemical signals, being detected via contact chemoreception and used during mate choice as in other insects. Gas chromatography shows that the subspecies have diverged in the composition of their cuticular hydrocarbons. This difference between subspecies exists over and above variation in cuticular hydrocarbons among individual populations. The majority of the difference can be attributed to the relative amounts of a small group of compounds present in the cuticle. The possible consequences of this chemical divergence for mating encounters between the subspecies are discussed. 相似文献
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4.
Normally, rats and mice eat chow-type rations. When fed sucha ration, body fat usually ranges between 11 and 18%. If a semi-purifieddiet high in fat is fed instead of the chow-type ration, somestrains of rats and mice respond by accumulating abnormal amountsof weight and fat. Their bodies now contain as much as 40% fatand fat depots are enlarged. Rats which respond to a high fatdiet with excessive weight and fat gain consume more kilocaloriesin the same time interval and are more efficient in energy utilizationthan rats of the same strain which consume a grain diet. Forthese rats, if medium-chain triglycerides are substituted forthe long-chain triglycerides in the high fat diet, there isa depression in food intake, accretion of body weight and fatas well as energy utilization. Blood makes up 3.5 to 5.1% of the fat organ weight. The lowervalue represents the quantity present in adipose tissue of obeserats while the higher value is for "normal-weight" rats. Thetriglyceride content of perirenal and epididymal fat depotsis around 90%. On the other hand, the triglyceride content ofinguinal fat tissue ranges from 56 to 80% and is affected bystrain, age and diet. If diets are high in fat, the proportionaldistribution of fatty acids in the adipose tissue reflects theproportional distribution in dietary fat, except when medium-chaintriglycerides are fed. 相似文献
5.
RACHEL M. LOCKLIN RICHARD O.C OREFFO JAMES T. TRIFFITT 《Cell biology international》1998,22(3):207-215
Cellular differentiation is controlled by a variety of factors including gene methylation, which represses particular genes as cell fate is determined. The incorporation of 5-azacytidine (5azaC) into DNA in vitro prevents methylation and thus can alter cellular differentiation pathways. Human bone marrow fibroblasts and MG63 cells treated with 5azaC were used as models of osteogenic progenitors and of a more mature osteoblast phenotype, respectively. The capacity for differentiation of these cells following treatment with glucocorticoids was investigated. 5azaC treatment led to significant expression of the osteoblastic marker alkaline phosphatase in MG63 osteosarcoma cells, which was further augmented by glucocorticoids; however, in human marrow fibroblasts alkaline phosphatase activity was only observed in glucocorticoid-treated cultures. MG63 cells represent a phenotype late in the osteogenic lineage in which demethylation is sufficient to induce alkaline phosphatase activity. Marrow fibroblasts are at an earlier stage of differentiation and require stimulation with glucocorticoids. In contrast, the expression of osteocalcin, an osteoblastic marker, was unaffected by 5azaC treatment, suggesting that regulation of expression of the osteocalcin gene does not involve methylation. These models provide novel approaches to the study of the control of differentiation in the marrow fibroblastic system. 相似文献
6.
Genetic variation in expression of defense phenotype may mediate evolutionary adaptation of Asclepias syriaca to elevated CO2 总被引:1,自引:0,他引:1
How species interactions may modify the effects of environmental change on evolutionary adaptation is poorly understood. Elevated CO2 is known to alter plant–herbivore interactions, but the evolutionary consequences for plant populations have received little attention. We conducted an experiment to determine the effects of elevated CO2 and herbivory by a specialist insect herbivore (Danaus plexippus) on the expression of constitutive and induced plant defense traits in five genotypes of Asclepias syriaca, and assessed the heritability of these traits. We also examined changes in relative fitness among plant genotypes in response to altered CO2 and herbivory. The expression of plant defense traits varied significantly among genotypes. Elevated CO2 increased plant growth and physical defenses (toughness and latex), but decreased investment in chemical defenses (cardenolides). We found no effect of elevated CO2 on plant induction of cardenolides in response to caterpillar herbivory. Elevated CO2 decreased the expression of chemical defenses (cardenolides) to a different extent depending on plant genotype. Differential effects of CO2 on plant defense expression, rather than direct effects on relative fitness, may alter A. syriaca adaptation to changing climate. 相似文献
7.
- 1 As companion animals, domestic cats Felis catus can attain very high densities, and have the potential to exert detrimental effects on prey species. Yet, there is a paucity of information on the impact of cat predation in urban areas, where most cats are likely to be present.
- 2 We quantified the minimum number of animals killed annually by cats in a 4.2-km2 area of Bristol, UK, by asking owners to record prey animals returned home by their pets. The potential impact of cat predation on prey species was estimated by comparing the number of animals killed with published estimates of prey density and annual productivity.
- 3 Predator density was 229 cats/km2.
- 4 Five mammal, 10 bird and one amphibian prey species were recorded. Mean predation rate was 21 prey/cat/annum. The most commonly recorded prey species was the wood mouse Apodemus sylvaticus.
- 5 Predation on birds was greatest in spring and summer, and probably reflected the killing of juvenile individuals. For three prey species (house sparrow Passer domesticus, dunnock Prunella modularis, robin Erithacus rubecula), estimated predation rates were high relative to annual productivity, such that predation by cats may have created a dispersal sink for juveniles from more productive neighbouring areas. The impact of cats on these species therefore warrants further investigation.
8.
The utility of morphological characters in gastropod phylogenetics: an example from the Calyptraeidae 总被引:3,自引:0,他引:3
RACHEL COLLIN 《Biological journal of the Linnean Society. Linnean Society of London》2003,78(4):541-593
Organismal taxonomy is often based on a single or a small number of morphological characters. When they are morphologically simple or known to be plastic, we may not have great confidence in the taxonomic conclusions of analyses based on these characters. For example, calyptraeid gastropod shells are well known for their simplicity and plasticity, and appear to be subject to frequent evolutionary convergences, but are nevertheless the basis for calyptraeid taxonomy. In a case like this, knowing how the pattern of relationships inferred from morphological features used in traditional taxonomy compares to the patterns of relationships inferred from other morphological characters or DNA sequence data would be useful. In this paper, I examine the relative utility of traditional taxonomic characters (shell characters), anatomical characters and molecular characters for reconstructing the phylogeny of calyptraeid gastropods. The results of an ILD test and comparisons of the recovered tree topologies suggest that there is conflict between the DNA sequence data and the morphological data. Very few of the nodes recovered by the morphological data were recovered by any other dataset. Despite this conflict, the inclusion of morphological data increased the resolution and support of nodes in the topology recovered from a combined dataset. The RIs and CIs of the morphological data on the best estimate topology were not any worse than these indices for the other datasets. This analysis demonstrates that although analyses can be misled by these convergences if morphological characters are used alone, these characters contribute significantly to the combined dataset. © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 78 , 541–593. 相似文献
9.
Adaptive radiations likely underlie much of the world’s diversity, especially that of hyper‐diverse regions. They are usually characterized by a burst of speciation early in their evolutionary history, a pattern which can be detected using population genetic tools. The Cape Floristic Region (CFR) of southwestern South Africa is home to many spectacular plant radiations. Here, we investigate the white proteas (Protea section Exsertae), a typical CFR radiation, to determine if it demonstrates the burst of speciation associated with adaptive radiations in recent models. Inferences from individual assignment, tree‐based population relationships, and pairwise F‐statistics based on 10 microsatellite loci reveal that while the white proteas radiated recently they did not radiate explosively. In addition, we found evidence that there is little gene flow between sampled populations of most species. Taken together, these results demonstrate that within a small clade, the processes underlying the radiation are different from those envisioned by current models of adaptive radiation and suggest that geographical isolation could have played a role in the diversification of the group. Our study implicates both adaptive and non‐adaptive processes in the evolution of botanical diversity of the CFR. 相似文献
10.
SUSANNAH M. HILL RACHEL URWIN TERESA F. KNAPP JULIAN M. CRAMPTON 《Medical and veterinary entomology》1991,5(4):455-463
The cloned DNA sequences pAna1, pAnq1 and pAnm14, which may be used to distinguish between at least five of the six species in the Anopheles gambiae Giles complex of Afrotropical malaria vector mosquitoes, have been sequenced. Each clone was found to possess a series of repeated sequences of 41, 30 and 163 bases respectively. In pAnq1 and pAnm14 the repeats were in direct tandem array, whilst in pAna1 the repetitive sequence was found to be interspersed by 15-17 variable bases. A comparison of a number of copies of each of the repetitive sequences within the three clones enabled the definition of the consensus sequence for each repetitive element. Based on these consensus sequences, three oligonucleotides of 21, 23 and 26 bases were derived from pAna1, pAnq1 and pAnm14 respectively. When tested as probes against DNA dot-blots and squash-blots of mosquito specimens, each oligonucleotide retained the same species-specificity as the original clones from which they were derived. The radioactively labelled oligonucleotides were able to detect as little as 5 ng of target genomic DNA in an overnight autoradiographic exposure. The synthetic DNA probes will form the basis of a simplified system for the field identification of Anopheles gambiae sibling species specimens. 相似文献