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Different species may respond differently to habitat fragmentation. Theory predicts that abundant generalist species should be less affected by fragmentation than specialist species. In ant communities, the most abundant species is often behaviourally dominant. Thus, habitat fragmentation could alter competitive interactions between the dominant ant species and the other species. We tested this hypothesis in a long-term grassland fragmentation experiment. Fragments of different size (20.25 and 2.25 m2) were isolated by a 5-m wide strip of frequently mown vegetation. Control plots were situated in adjacent undisturbed grassland. Ant density and species composition were assessed 3 and 6 years after initiation of the experimental fragmentation. The effect of the dominant ant species on the resource use of the other species was examined at natural sugar resources (aphids and extrafloral nectaries) and at artificial sugar baits. Lasius paralienus was the most abundant ant species (72% of nests) in the grasslands examined. Species richness and forager density in the other species decreased with increasing density of L. paralienus in fragments but not in control plots. The overall forager density of the other species was positively related to their habitat niche overlap with L. paralienus. The density of foragers of the other species at sugar resources was not affected by L. paralienus forager density. The experimental fragmentation resulted in an increase in natural sugar resources in fragments. This may have reduced the intensity of interspecific competition for sugar resources. Our study shows that the grassland fragmentation altered interactions between the dominant L. paralienus and the other ant species.Electronic Supplementary Material Supplementary material is available for this article at 相似文献
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Despite the potential pitfalls of stratification, population-based association studies nowadays are being conducted more often than family-based association studies. However, the mechanism of genomic imprinting has lately been implicated in the etiology of genetic complex diseases and can be detected using statistics only in family-based designs. Powerful tests for association and imprinting have been proposed previously for case-parent trios and single markers. Since the power of association studies can be improved if multiple affected children and haplotypes are considered, we extended the parental asymmetry test (PAT) for imprinting to a test that is suited for both general nuclear families and haplotypes, called HAP-PAT. Significance of the HAP-PAT is determined via a Monte-Carlo simulation procedure. In addition to the HAP-PAT, we modified a haplotype-based association test, proposed by us before, in such a way that either only paternal or maternal transmissions contribute to the test statistic. The approaches were implemented in FAMHAP and we evaluated their performance under a variety of disease models. We were able to demonstrate the usefulness of our haplotype-based approaches to detect parent-of-origin effects. Furthermore, we showed that also in the presence of imprinting it is more reasonable to consider all affected children of a nuclear family, than to randomly select one affected child from each family and to conduct a trio study using the selected individuals. 相似文献
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Kikkert JR Hoepting CA Wu Q Wang P Baur R Shelton AM 《Journal of economic entomology》2006,99(4):1310-1315
The midge Contarinia nasturtii Kieffer (Diptera: Cecidomyiidae) was first confirmed in North America in Ontario, Canada, in 2000. The insect is now distributed throughout many counties in the provinces of Ontario and Québec. Nearly 1,200 farms in the northeastern United States that grow cruciferous vegetables are at risk for C. nasturtii infestation if this insect were to spread to that region. Over a period of 3 yr (2002-2004), approximately 3,000 ha of crops on 94 farms in western New York State was scouted for C. nasturtii, but none were found. In 2004, 42 experimental pheromone traps were placed in fields of cruciferous vegetables in eight counties. C. nasturtii males were captured at low levels (1-50 per trap / 8 wk) on four farms in Niagara County, but not at any other site. C. nasturtii larvae were found in plant tissue at one of the four farms. Insect specimens were identified by morphological methods, molecular methods, or both. This is the first confirmation of C. nasturtii in the United States, which we believe was made possible by the combined use of pheromone traps, morphological characters of trapped adults, and molecular methods. The early detection in New York presents an opportunity to implement measures to limit the spread and establishment of C. nasturtii across the state and into other regions of the United States. 相似文献
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We show that the five subunits of a gamma-aminobutyric acid type A receptor (GABA(A) receptor) can be concatenated to yield a functional receptor. This concatenated receptor alpha(1)-beta(2)-alpha(1)-gamma(2)-beta(2) has the advantage of a known subunit arrangement. Most of its functional properties are not significantly different from a receptor formed by individual subunits. Extent of expression amounted to about 40% of that of non-concatenated receptors in Xenopus oocytes, after injection of oocytes with comparable amounts of cRNA coding for concatenated and non-concatenated receptors. The ability to express receptors consisting of five subunits enables detailed studies of GABA(A) receptor subtype selective compounds. 相似文献
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Fackler OT Wolf D Weber HO Laffert B D'Aloja P Schuler-Thurner B Geffin R Saksela K Geyer M Peterlin BM Schuler G Baur AS 《Current biology : CB》2001,11(16):1294-1299
In the infected host, the Nef protein of HIV/SIV is required for high viral loads and thus disease progression. Recent evidence indicates that Nef enhances replication in the T cell compartment after the virus is transmitted from dendritic cells (DC). The underlying mechanism, however, is not clear. Here, we report that a natural variability in the proline-rich motif (R71T) profoundly modulated Nef-stimulated viral replication in primary T cells of immature dendritic cell/T cell cocultures. Whereas both Nef variants (R/T-Nef) downregulated CD4, only the isoform supporting viral replication (R-Nef) efficiently interacted with signaling molecules of the T cell receptor (TCR) environment and stimulated cellular activation. Structural analysis suggested that the R to T conversion induces conformational changes, altering the flexibility of the loop containing the PxxP motif and hence its ability to bind cellular partners. Our report suggests that functionally and conformationally distinct Nef isoforms modulate HIV replication on the interaction level with the TCR-signaling environment once the virus enters the T cell compartment. 相似文献
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Christina Westermann Daria S. Zhurina Annika Baur Wei Shang Jing Yuan Christian U. Riedel 《Symbiosis (Philadelphia, Pa.)》2012,58(1-3):191-200
Bifidobacterium bifidum S17 is a promising probiotic candidate, which displays potent anti-inflammatory activity both in vitro and in vivo. Furthermore, tight adhesion to intestinal epithelial cells (IECs) has been shown for this strain and is considered to be an important prerequisite for host colonization and consequently the anti-inflammatory properties. By analyzing the recently sequenced genome at least 9 surface proteins and various gene clusters encoding for putative pili were identified. Most of these proteins are expressed in vitro, with higher expression during exponential growth phase. Increased expression of the putative adhesins in exponential growth phase was associated with higher adhesion of B. bifidum S17 to Caco-2 cells. 相似文献