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841.
Manuel A. Arteaga Juan D. Delgado Rüdiger Otto José M. Fernández-Palacios José R. Arévalo 《Biological invasions》2009,11(4):1071-1086
Islands are paradigms of the pervasive spread of alien plants, but little work has been done assessing pattern and cause of
the distribution of such plants in relation to roads on oceanic islands. We studied richness, composition, and distribution
of alien plants and compared them with native species along roads on Tenerife (Canary Islands). We studied a single road transect
that sampled two contrasting wind-facing aspects (leeward versus windward) and ran from coastal Euphorbia scrubland through thermophilous scrubland to Makaronesian laurel forest at the top of a mountainous massif. We evaluated
the effects of elevation, aspect, distance to urban nuclei, and several road-edge features (including road-edge width and
management—implying disturbance intensity), using regression models, analysis of variance, and multivariate ordination methods.
Richness of both endemics and native nonendemics was explained by elevation (related to well-defined vegetation belts), steepness
of the edge slope, and cover of rocky ground. Despite a short elevational gradient (0–650 m), we found clear altitudinal zonation
by biogeographic origin of both nonendemic natives and aliens, and altitudinal distribution of aliens followed the same zonation
as that of natives. Alien species’ richness was related to management intensity determining edge disturbance, road-edge width,
and distance to the nearest urban nuclei (propagule sources). Different variables explained distribution patterns of natives,
endemics, and aliens along roadsides on leeward and windward aspects. Altitude and aspect also had a strong influence on the
frequency of life strategies (woody species, annuals and biennial/perennial herbs) of roadside plant communities. Due to harsher
environmental filters operating on the leeward aspect, alien species were distributed along the altitudinal gradient in apparent
consistency with general biogeographical affinities. Tropical/subtropical taxa showed exponential decrease with increasing
elevation, Mediterranean taxa showed a unimodal response (i.e., maximum richness at mid elevation, minimum at the extremes
of the gradient), and temperate taxa showed linear increase with elevation. Native but nonendemic species followed analogous
trends to those of aliens. This suggests climatic matching as a prerequisite for successful invasion of this topographically
complex island. Other road traits, such as edge width, slope steepness, soil cover, and road-edge disturbance intensity may
play a complementary role, at a more local scale, to shape the distribution of alien plants on these island roads. 相似文献
842.
843.
Mary A. Robinson Stephen W. Tuttle Cynthia M. Otto Cameron J. Koch 《Free radical biology & medicine》2010,48(2):189-195
Stimulated macrophages produce nitric oxide (NO) via inducible nitric oxide synthase (iNOS) using molecular O2, L-arginine, and NADPH. Exposure of macrophages to hypoxia decreases NO production within seconds, suggesting substrate limitation as the mechanism. Conflicting data exist regarding the effect of pO2 on NADPH production via the oxidative pentose phosphate cycle (OPPC). Therefore, the present studies were developed to determine whether NADPH could be limiting for NO production under hypoxia. Production of NO metabolites (NOx) and OPPC activity by RAW 264.7 cells was significantly increased by stimulation with lipopolysaccharide (LPS) and interferon γ (IFNγ) at pO2 ranging from 0.07 to 50%. OPPC activity correlated linearly with NOx production at pO2 > 0.13%. Increased OPPC activity by stimulated RAW 264.7 cells was significantly reduced by 1400 W, an iNOS inhibitor. OPPC activity was significantly increased by concomitant treatment of stimulated RAW 264.7 cells with chemical oxidants such as hydroxyethyldisulfide or pimonidazole, at 0.07 and 50% O2, without decreasing NOx production. These results are the first to investigate the effect of pO2 on the relationship between NO production and OPPC activity, and to rule out limitations in OPPC activity as a mechanism by which NO production is decreased under hypoxia. 相似文献
844.
Peter A. Lind Christina Tobin Otto G. Berg Charles G. Kurland Dan I. Andersson 《Molecular microbiology》2010,75(5):1078-1089
Genes introduced by gene replacements and other types of horizontal gene transfer (HGT) represent a significant presence in many archaeal and eubacterial genomes. Most alien genes are likely to be neutral or deleterious upon arrival and their long‐term persistence may require a mechanism that improves their selective contribution. To examine the fate of inter‐species gene replacements, we exchanged three native S. typhimurium genes encoding ribosomal proteins with orthologues from various other microbes. The results show that replacement of each of these three genes reduces fitness to such an extent that it would provide an effective barrier against inter‐species gene replacements in eubacterial populations. However, these fitness defects could be partially ameliorated by gene amplification that augmented the dosage of the heterologous proteins. This suggests that suboptimal expression is a common fitness constraint for inter‐species gene replacements, with fitness costs conferred by either a lower expression level of the alien protein compared with the native protein or a requirement for an increased amount of the alien protein to maintain proper function. Our findings can explain the observation that duplicated genes are over‐represented among horizontally transferred genes, and suggest a potential coupling between compensatory gene amplification after HGT and the evolution of new genes. 相似文献
845.
The Drosophila genome contains at least three loci for the Na,K-ATPase β-subunit; however, only the protein products of nrv1 and nrv2 have been characterized hitherto. Here, we provide evidence that nrv3 also encodes for a functional Na,K-ATPase β-subunit, as its protein product co-precipitates with the Na,K-ATPase α-subunit.
Nrv3 expression in adult flies is restricted to the nervous system in which Nrv3 is enriched in selective types of sensory
cells. Because Nrv3 expression is especially prominent in the compound eye, we have analyzed the subcellular and developmental
distribution of Nrv3 within the visual cells and related this distribution to those of the α-subunit and of the β-subunits
Nrv1 and Nrv2. Prospective visual cells express Nrv2 in the third larval instar stage and during the first half of pupal development.
During the last third of pupal life, Nrv3 gradually replaces Nrv2 as the Na,K-ATPase β-subunit in the photoreceptor cells.
Adult photoreceptors express Nrv3 as their major β-subunit; the visual cells R1–R6 co-express Nrv2 at a low level, whereas
R7 and R8 co-express Nrv1. Notably, β-subunits do not co-distribute exactly with the α-subunit at some developmental stages,
supporting the concept that the α-subunit and β-subunit can exist in the plasma membrane without being engaged in α/β heterodimers.
The non-visual cells within the compound eye express almost exclusively Nrv2, which segregates together with the α-subunit
to septate junctions throughout development. 相似文献
846.
Chandrashekhar U. Murade Vinod Subramaniam Cees Otto Martin L. Bennink 《Nucleic acids research》2010,38(10):3423-3431
When individual dsDNA molecules are stretched beyond their B-form contour length, they reveal a structural transition in which the molecule extends 1.7 times its contour length. The nature of this transition is still a subject of debate. In the first model, the DNA helix unwinds and combined with the tilting of the base pairs (which remain intact), results in a stretched form of DNA (also known as S-DNA). In the second model the base pairs break resulting effectively in two single-strands, which is referred to as force-induced melting. Here a combination of optical tweezers force spectroscopy with fluorescence microscopy was used to study the structure of dsDNA in the overstretching regime. When dsDNA was stretched in the presence of 10 nM YOYO-1 an initial increase in total fluorescence intensity of the dye–DNA complex was observed and at an extension where the dsDNA started to overstretch the fluorescence intensity leveled off and ultimately decreased when stretched further into the overstretching region. Simultaneous force spectroscopy and fluorescence polarization microscopy revealed that the orientation of dye molecules did not change significantly in the overstretching region (78.0°± 3.2°). These results presented here clearly suggest that, the structure of overstretched dsDNA can be explained accurately by force induced melting. 相似文献
847.
Jonathan A. Mee Sarah P. Otto 《Evolution; international journal of organic evolution》2010,64(10):2808-2819
In several asexual taxa, reproduction requires mating with related sexual species to stimulate egg development, even though genetic material is not incorporated from the sexuals (gynogenesis). In cases in which gynogens do not invest in male function, they can potentially have a twofold competitive advantage over sexuals because the asexuals avoid the cost of producing males. If unmitigated, however, the competitive success of the asexuals would ultimately lead to their own demise, following the extinction of the sexual species that stimulate egg development. We have studied a model of mate choice among sexual individuals and asexual gynogens, where males of the sexual species preferentially mate with sexual females over gynogenetic females, to determine if such mating preferences can stably maintain both gynogenetic and sexual individuals within a community. Our model shows that stable coexistence of gynogens and their sexual hosts can occur when there is variation among males in the degree of preference for mating with sexual females and when pickier males pay a higher cost of preference. 相似文献
848.
Brent G. Pautler Janice Austin Angelika Otto Kailey Stewart Scott F. Lamoureux Myrna J. Simpson 《Biogeochemistry》2010,98(1-3):75-87
This paper presents an uncomplicated approach to improve estimates of groundwater nutrient load to a marine embayment. A two-dimensional chemical profile of shallow groundwater was analysed in a sandy beach in three seasons (early summer, late summer and mid winter) and an adjusted estimate of groundwater nutrient discharge was derived that accounts for a complex biogeochemical environment and non-conservative behaviour of nutrients in the pre-discharge beach groundwater. The study was conducted at Cockburn Sound, Western Australia, where there has been significant groundwater contamination and associated marine ecological degradation. Losses in nitrogen and increases in phosphorus were observed along the discharge pathway beyond that expected from mixing with marine water, and the changes were attributed to chemically and biologically mediated reactions. A slow groundwater velocity (0.14–0.18 m day?1), high organic carbon (TOC = 0.35–4.9 mmol l?1, DOC = 0.28–4.6 mmol l?1) and low to sub-oxic conditions (DO = 0.4–24% saturation) were deemed suitable for chemically and biologically mediated reactions to occur and subsequently alter regional estimates of groundwater nutrient concentration. Accounting for this environment, groundwater loads were calculated that were 1–2 orders of magnitude less than previous regional-based estimates: 0.4–13 kg NO x ? day?1, 0.2–24 kg NH4 + day?1 and 0.004–0.8 kg FRP day?1. This paper applies knowledge of recent research and presents scope to marine managers or modellers to account for groundwater inputs to the marine environment. 相似文献
849.
J. R. Arévalo R. Otto C. Escudero S. Fernández-Lugo M. Arteaga J. D. Delgado J. M. Fernández-Palacios 《Plant Ecology》2010,209(1):23-35
Biological homogenization is defined as a process that occurs when native species are replaced by common and dominant exotic
species or due to depletion and expansion of native species, reducing the beta diversity between areas or habitats. Islands
are particularly vulnerable to plant invasion, and as a consequence, homogenization is a process that can become faster and
more intense in islands than in continental areas. We recorded vascular plant species composition in roadside communities
along a strong altitudinal gradient using plots beside the road and at two distances from the road (0–50 and 50–100 m). We
analyzed the results separately for each group of plots with a Detrended Correspondence Analysis (DCA) including and excluding
exotic species. The results revealed that where exotic species were most abundant, i.e., at the road edge, they can create
an effect of floristic homogenization where three similar roads are compared. At a distance of >50 m from the road, where
exotic species are less frequent, this effect has already disappeared, indicating that it is a local phenomenon, closely related
to the highly disturbed roadside environment. Furthermore, floristic homogenization seems to be more important at higher altitudes
(>1000 m), probably related to higher diversity in native plant communities and lower levels of human disturbances. Roads
allow humans to reach relatively remote and sometimes well-conserved areas, and, at the same time, facilitate the spread of
exotic plants and the most common native species which can locally create floristic homogenization in roadside communities
on this oceanic island. A deeper understanding of the effects of these anthropogenic corridors at the local and regional scales
is therefore required to integrate road planning and management with the aim of conserving the value of the natural areas. 相似文献
850.
Christoph Kueffer Curtis C. Daehler Christian W. Torres-Santana Christophe Lavergne Jean-Yves Meyer Rüdiger Otto Luís Silva 《Perspectives in Plant Ecology, Evolution and Systematics》2010,12(2):145-161
Oceanic islands have long been considered to be particularly vulnerable to biotic invasions, and much research has focused on invasive plants on oceanic islands. However, findings from individual islands have rarely been compared between islands within or between biogeographic regions. We present in this study the most comprehensive, standardized dataset to date on the global distribution of invasive plant species in natural areas of oceanic islands. We compiled lists of moderate (5–25% cover) and dominant (>25% cover) invasive plant species for 30 island groups from four oceanic regions (Atlantic, Caribbean, Pacific, and Western Indian Ocean). To assess consistency of plant behaviour across island groups, we also recorded present but not invasive species in each island group.We tested the importance of different factors discussed in the literature in predicting the number of invasive plant species per island group, including island area and isolation, habitat diversity, native species diversity, and human development. Further we investigated whether particular invasive species are consistently and predictably invasive across island archipelagos or whether island-specific factors are more important than species traits in explaining the invasion success of particular species.We found in total 383 non-native spermatophyte plants that were invasive in natural areas on at least one of the 30 studied island groups, with between 3 and 74 invaders per island group. Of these invaders about 50% (181 species) were dominants or co-dominants of a habitat in at least one island group. An extrapolation from species accumulation curves across the 30 island groups indicates that the total current flora of invasive plants on oceanic islands at latitudes between c. 35°N and 35°S may eventually consist of 500–800 spermatophyte species, with 250–350 of these being dominant invaders in at least one island group. The number of invaders per island group was well predicted by a combination of human development (measured by the gross domestic product (GDP) per capita), habitat diversity (number of habitat types), island age, and oceanic region (87% of variation explained). Island area, latitude, isolation from continents, number of present, non-native species with a known invasion history, and native species richness were not retained as significant factors in the multivariate models.Among 259 invaders present in at least five island groups, only 9 species were dominant invaders in at least 50% of island groups where they were present. Most species were invasive only in one to a few island groups although they were typically present in many more island groups. Consequently, similarity between island groups was low for invader floras but considerably higher for introduced (but not necessarily invasive) species – especially in pairs of island groups that are spatially close or similar in latitude. Hence, for invasive plants of natural areas, biotic homogenization among oceanic islands may be driven by the recurrent deliberate human introduction of the same species to different islands, while post-introduction processes during establishment and spread in natural areas tend to reduce similarity in invader composition between oceanic islands. We discuss a number of possible mechanisms, including time lags, propagule pressure, local biotic and abiotic factors, invader community assembly history, and genotypic differences that may explain the inconsistent performance of particular invasive species in different island groups. 相似文献