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121.
CHARLES L. ROSS JAMES H. BENEDIX JR CHRISTOPHER GARCIA KALLI LAMBETH RACHEL PERRY † VANESSA SELWYN DANIEL J. HOWARD 《Biological journal of the Linnean Society. Linnean Society of London》2008,94(4):777-796
The structure of the hybrid zone between the ground crickets, Allonemobius socius and Allonemobius fasciatus , approximates an environmental mosaic based on temperature/moisture at regional spatial scales. In the present study, we show that the micro-geographic spatial structure (i.e. single fields) of this hybrid zone is governed by the same criteria. Thus, the criteria that structure this hybrid zone are scale independent, even though the agents that implement these criteria may differ at various scales (climate, latitude, and elevation at regional scales; grass height, slope aspect, and field use at micro-geographic scales). Additionally, the study demonstrates a previously unknown barrier to genetic exchange in this system that acts before conspecific sperm precedence. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 777–796. 相似文献
122.
Decline in a dominant invertebrate species contributes to altered carbon cycling in a low-diversity soil ecosystem 总被引:1,自引:0,他引:1
J. E. BARRETT ROSS A. VIRGINIA† DIANA H. WALL‡ BYRON J. ADAMS§ 《Global Change Biology》2008,14(8):1734-1744
Low-diversity ecosystems cover large portions of the Earth's land surface, yet studies of climate change on ecosystem functioning typically focus on temperate ecosystems, where diversity is high and the effects of individual species on ecosystem functioning are difficult to determine. We show that a climate-induced decline of an invertebrate species in a low-diversity ecosystem could contribute to significant changes in carbon (C) cycling. Recent climate variability in the McMurdo Dry Valleys of Antarctica is associated with changes in hydrology, biological productivity, and community composition of terrestrial and aquatic ecosystems. One of the greatest changes documented in the dry valleys is a 65% decrease in the abundance of the dominant soil invertebrate ( Scottnema lindsayae , Nematoda) between 1993 and 2005, illustrating sensitivity of biota in this ecosystem to small changes in temperature. Globally, such declines are expected to have significant influences over ecosystem processes such as C cycling. To determine the implications of this climate-induced decline in nematode abundance on soil C cycling we followed the fate of a 13 C tracer added to soils in Taylor Valley, Antarctica. Carbon assimilation by the dry valley nematode community contributed significantly to soil C cycling (2–7% of the heterotrophic C flux). Thus, the influence of a climate-induced decline in abundance of a dominant species may have a significant effect on ecosystem functioning in a low-diversity ecosystem. 相似文献
123.
Elevated atmospheric CO2 stimulates aboveground biomass in a fire-regenerated scrub-oak ecosystem 总被引:2,自引:0,他引:2
Paul Dijkstra Graham Hymus Debra Colavito David A. Vieglais† Christina M. Cundari‡ David P. Johnson Bruce A. Hungate§ C. ROSS Hinkle‡ Bert G. Drake 《Global Change Biology》2002,8(1):90-103
The effect of elevated atmospheric CO2 concentration (Ca) on the aboveground biomass of three oak species, Quercus myrtifolia, Q. geminata, and Q. chapmanii, was estimated nondestructively using allometric relationships between stem diameter and aboveground biomass after four years of experimental treatment in a naturally fire‐regenerated scrub‐oak ecosystem. After burning a stand of scrub‐oak vegetation, re‐growing plants were exposed to either current ambient (379 µL L?1 CO2) or elevated (704 µL L?1 CO2) Ca in 16 open‐top chambers over a four‐year period, and measurements of stem diameter were carried out annually on all oak shoots within each chamber. Elevated Ca significantly increased aboveground biomass, expressed either per unit ground area or per shoot; elevated Ca had no effect on shoot density. The relative effect of elevated Ca on aboveground biomass increased each year of the study from 44% (May 96–Jan 97), to 55% (Jan 97–Jan 98), 66% (Jan 98–Jan 99), and 75% (Jan 99–Jan 00). The effect of elevated Ca was species specific: elevated Ca significantly increased aboveground biomass of the dominant species, Q. myrtifolia, and tended to increase aboveground biomass of Q. chapmanii, but had no effect on aboveground biomass of the subdominant, Q. geminata. These results show that rising atmospheric CO2 has the potential to stimulate aboveground biomass production in ecosystems dominated by woody species, and that species‐specific growth responses could, in the long term, alter the composition of the scrub‐oak community. 相似文献
124.
Rick Brouwer Wilma TM Vree Egberts Gerald JD Hengstman Reinout Raijmakers Baziel GM van Engelen Hans Peter Seelig Manfred Renz Rudolf Mierau Ekkehard Genth Ger JM Pruijn Walther J van Venrooij 《Arthritis research & therapy》2001,4(2):1-5
The autoantigenic polymyositis/scleroderma (PM/Scl) complex was recently shown to be the human homologue of the yeast exosome, which is an RNA-processing complex. Our aim was to assess whether, in addition to targeting the known autoantigens PM/Scl-100 and PM/Scl-75, autoantibodies also target recently identified components of the PM/Scl complex. The prevalence of autoantibodies directed to six novel human exosome components (hRrp4p, hRrp40p, hRrp41p, hRrp42p, hRrp46p, hCsl4p) was determined in sera from patients with idiopathic inflammatory myopathy (n = 48), scleroderma (n = 11), or the PM/Scl overlap syndrome (n = 10). The sera were analyzed by enzyme-linked immunosorbent assays and western blotting using the affinity-purified recombinant proteins. Our results show that each human exosome component is recognized by autoantibodies. The hRrp4p and hRrp42p components were most frequently targeted. The presence of autoantibodies directed to the novel components of the human exosome was correlated with the presence of the anti-PM/Scl-100 autoantibody in the sera of patients with idiopathic inflammatory myopathy (IIM), as was previously found for the anti-PM/Scl-75 autoantibody. Other clear associations between autoantibody activities were not found. These results further support the conception that the autoimmune response may initially be directed to PM/Scl-100, whereas intermolecular epitope spreading may have caused the autoantibody response directed to the associated components. 相似文献
125.
A characteristic feature of the sperm P1 protamines of eutherian mammals is
the constant presence of six to nine cysteine residues per molecule. During
spermiogenesis these residues become oxidized to form a three-dimensional
network of disulfide bridges between, and within, protamine molecules in
the sperm chromatin. This covalent cross linking strongly stabilizes
eutherian sperm nuclei. In contrast, protamines sequenced from teleost
fish, birds, monotremes, and marsupials all lack cysteine residues and
their sperm nuclei, without the stabilizing cross links, are easily
decondensed in vitro. We have now found that one genus of tiny, shrewlike
dasyurid marsupials, the Planigales, possess P1 protamines containing five
to six cysteine residues. These residues appear to have evolved since the
divergence of Planigales from other members of the family Dasyuridae, such
as the marsupial mouse, Sminthopsis crassicaudata. We believe this
constitutes a case of convergent evolution in a subfamily of dasyurid
marsupials toward the cysteine-rich eutherian form of sperm protamine P1.
相似文献
126.
GRACIELA GARCÍA-GUZMÁAN JEREMY J. BURDON JULIAN E. ASH ROSS B. CUNNINGHAM 《The New phytologist》1996,132(3):459-469
127.
THE DEVELOPMENT OF ENDOMYCORRHIZAL ROOT SYSTEMS 总被引:5,自引:5,他引:0
128.
129.
130.
Abstract The grey mangrove tree, Avicennia marina, forms a hard substratum in an area otherwise dominated by soft-sediment. Various intertidal organisms attach to and move about on the trees. The abundant barnacles Elminius covenus, Hexaminius popeiana and Hexaminius foliorum live on a variety of substrata in mangrove forests. Their patterns of distribution and abundance were recorded and models proposed to explain these patterns. Densities of barnacles on bark, leaves and twigs of A. marina were estimated in a locality near Sydney. Elminius covenus were more abundant on bark than on leaves or twigs of A. marina. Hexaminius popeiana, although less abundant on bark than E. covenus, were not found on twigs or leaves. In contrast, H. foliorum were more abundant on twigs than leaves and were not found on the bark of A. marina. Densities of barnacles were greater in the seaward than in landward parts of the forest. Elminius covenus were the most abundant barnacles, H. foliorum were less abundant and H. popeiana were virtually absent in the landward zone. Barnacles in the seaward zone were most abundant at mid-tidal levels, less at high and low tidal levels of trunks and more abundant on lower than upper surfaces of trunks and leaves. The densities of barnacles differed according to the orientation of the bark or leaf. Models are proposed to explain the patterns of distribution and abundance of these barnacles. Each involves larval supply, settlement and post-settlement mortality. It is concluded that similar processes determining patterns of distribution and abundance for sessile organisms living on rock platforms may be applicable to sessile organisms living in the very different habitats of mangrove forests. 相似文献