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The invasive freshwater snail Tarebia granifera (Lamarck, 1822) was first reported in South Africa in 1999 and it has become widespread across the country, with some evidence to suggest that it reduces benthic macroinvertebrate biodiversity. The current study aimed to identify the primary abiotic drivers behind abundance patterns of T. granifera, by comparing the current abundance of the snail in three different regions, and at three depths, of the highly modified Nseleni River in KwaZulu-Natal, South Africa. Tarebia granifera was well established throughout the Nseleni River system, with an overall preference for shallow waters and seasonal temporal patterns of abundance. Although it is uncertain what the ecological impacts of the snail in this system are, its high abundances suggest that it should be controlled where possible and prevented from invading other systems in the region. 相似文献
84.
Achieving atomic-level accuracy in comparative protein models is limited by our ability to refine the initial, homolog-derived model closer to the native state. Despite considerable effort, progress in developing a generalized refinement method has been limited. In contrast, methods have been described that can accurately reconstruct loop conformations in native protein structures. We hypothesize that loop refinement in homology models is much more difficult than loop reconstruction in crystal structures, in part, because side-chain, backbone, and other structural inaccuracies surrounding the loop create a challenging sampling problem; the loop cannot be refined without simultaneously refining adjacent portions. In this work, we single out one sampling issue in an artificial but useful test set and examine how loop refinement accuracy is affected by errors in surrounding side-chains. In 80 high-resolution crystal structures, we first perturbed 6-12 residue loops away from the crystal conformation, and placed all protein side chains in non-native but low energy conformations. Even these relatively small perturbations in the surroundings made the loop prediction problem much more challenging. Using a previously published loop prediction method, median backbone (N-Calpha-C-O) RMSD's for groups of 6, 8, 10, and 12 residue loops are 0.3/0.6/0.4/0.6 A, respectively, on native structures and increase to 1.1/2.2/1.5/2.3 A on the perturbed cases. We then augmented our previous loop prediction method to simultaneously optimize the rotamer states of side chains surrounding the loop. Our results show that this augmented loop prediction method can recover the native state in many perturbed structures where the previous method failed; the median RMSD's for the 6, 8, 10, and 12 residue perturbed loops improve to 0.4/0.8/1.1/1.2 A. Finally, we highlight three comparative models from blind tests, in which our new method predicted loops closer to the native conformation than first modeled using the homolog template, a task generally understood to be difficult. Although many challenges remain in refining full comparative models to high accuracy, this work offers a methodical step toward that goal. 相似文献
85.
Ritha JA Njau Don de Savigny Lucy Gilson Eleuther Mwageni Franklin W Mosha 《Malaria journal》2009,8(1):1-27
Background
In the past decade there has been increasing visibility of malaria control efforts at the national and international levels. The factors that have enhanced this scenario are the availability of proven interventions such as artemisinin-based combination therapy, the wide scale use of insecticide-treated nets (ITNs) and a renewed emphasis in indoor residual house-spraying. Concurrently, there has been a window of opportunity of financial commitments from organizations such as the Global Fund for HIV/AIDS, Tuberculosis and Malaria (GFATM), the President's Malaria Initiative and the World Bank Booster programme.Methods
The case study uses the health policy analysis framework to analyse the implementation of a public-private partnership approach embarked upon by the government of Tanzania in malaria control – 'The Tanzania National Voucher Scheme'- and in this synthesis, emphasis is on the challenges faced by the scheme during the pre-implementation (2001 – 2004) and implementation phases (2004 – 2005). Qualitative research tools used include: document review, interview with key informants, stakeholder's analysis, force-field analysis, time line of events, policy characteristic analysis and focus group discussions. The study is also complemented by a cross-sectional survey, which was conducted at the Rufiji Health Demographic Surveillance Site, where a cohort of women of child-bearing age were followed up regarding access and use of ITNs.Results
The major challenges observed include: the re-introduction of taxes on mosquito nets and related products, procurement and tendering procedures in the implementation of the GFATM, and organizational arrangements and free delivery of mosquito nets through a Presidential initiative.Conclusion
The lessons gleaned from this synthesis include: (a) the consistency of the stakeholders with a common vision, was an important strength in overcoming obstacles, (b) senior politicians often steered the policy agenda when the policy in question was a 'crisis event', the stakes and the visibility were high, (c) national stakeholders in policy making have an advantage in strengthening alliances with international organizations, where the latter can become extremely influential in solving bottlenecks as the need arises, and (d) conflict can be turned into an opportunity, for example the Presidential initiative has inadvertently provided Tanzania with important lessons in the organization of 'catch-up' campaigns. 相似文献86.
Body mass reconstructions of extinct vertebrates are most robust when complete to near-complete skeletons allow the reconstruction of either physical or digital models. Digital models are most efficient in terms of time and cost, and provide the facility to infinitely modify model properties non-destructively, such that sensitivity analyses can be conducted to quantify the effect of the many unknown parameters involved in reconstructions of extinct animals. In this study we use laser scanning (LiDAR) and computer modelling methods to create a range of 3D mass models of five specimens of non-avian dinosaur; two near-complete specimens of Tyrannosaurus rex, the most complete specimens of Acrocanthosaurus atokensis and Strutiomimum sedens, and a near-complete skeleton of a sub-adult Edmontosaurus annectens. LiDAR scanning allows a full mounted skeleton to be imaged resulting in a detailed 3D model in which each bone retains its spatial position and articulation. This provides a high resolution skeletal framework around which the body cavity and internal organs such as lungs and air sacs can be reconstructed. This has allowed calculation of body segment masses, centres of mass and moments or inertia for each animal. However, any soft tissue reconstruction of an extinct taxon inevitably represents a best estimate model with an unknown level of accuracy. We have therefore conducted an extensive sensitivity analysis in which the volumes of body segments and respiratory organs were varied in an attempt to constrain the likely maximum plausible range of mass parameters for each animal. Our results provide wide ranges in actual mass and inertial values, emphasizing the high level of uncertainty inevitable in such reconstructions. However, our sensitivity analysis consistently places the centre of mass well below and in front of hip joint in each animal, regardless of the chosen combination of body and respiratory structure volumes. These results emphasize that future biomechanical assessments of extinct taxa should be preceded by a detailed investigation of the plausible range of mass properties, in which sensitivity analyses are used to identify a suite of possible values to be tested as inputs in analytical models. 相似文献
87.
P. A. Donald P. E. Pierson S. K. St. Martin P. R. Sellers G. R. Noel A. E. MacGuidwin J. Faghihi V. R. Ferris C. R. Grau D. J. Jardine H. Melakeberhan T. L. Niblack W. C. Stienstra G. L. Tylka T. A. Wheeler D. S. Wysong 《Journal of nematology》2006,38(1):76-82
The soybean cyst nematode Heterodera glycines (SCN) is of major economic importance and widely distributed throughout soybean production regions of the United States where different maturity groups with the same sources of SCN resistance are grown. The objective of this study was to assess SCN-resistant and -susceptible soybean yield responses in infested soils across the north-central region. In 1994 and 1995, eight SCN-resistant and eight SCN-susceptible public soybean cultivars representing maturity groups (MG) I to IV were planted in 63 fields, either infested or noninfested, in 10 states in the north-central United States. Soil samples were taken to determine initial SCN population density and race, and soil classification. Data were grouped for analysis by adaptation based on MG zones. Soybean yields were 658 to 3,840 kg/ha across the sites. Soybean cyst nematode-resistant cultivars yielded better at SCN-infested sites but lost this superiority to susceptible soybean cultivars at noninfested sites. Interactions were observed among initial SCN population density, cultivar, and location. This study showed that no region-wide predictive equations could be developed for yield loss based on initial nematode populations in the soil and that yield loss due to SCN in our region was greatly confounded by other stress factors, which included temperature and moisture extremes. 相似文献
88.
Kerry Kilshaw Penelope Sellers Sandra E. Baker David W. Macdonald Paul J. Johnson 《Acta theriologica》2011,56(2):149-155
We examined the potential of hare sightings data, collected during hunts by the Association of Masters of Harriers and Beagles,
as a possible monitoring tool for the European brown hare Lepus europaeus. The relationship between land use and both temporal trends, and spatial patterns, in brown hare sightings across England
and Wales was examined using data collected between the 1985/86 and 2004/05 hunting seasons. Hare sightings increased significantly
during this period, with an average increase of 2.81 hare sightings per hunting day across all hunts since 1985. Sightings
were more frequent in eastern England, where arable land is abundant, than in the rest of England and Wales which is predominantly
pastoral. There was no correlation between temporal trends in hare sightings and land use change. Patterns observed using
the hunt sighting data are similar to those reported by other concurrent studies that used different methods. We conclude
that hunt sightings could contribute useful data to a national monitoring scheme. 相似文献
89.
90.
Anika I Tsuchida Michiel Beekhuizen Marieke C ‘t Hart Timothy RDJ Radstake Wouter JA Dhert Daniel BF Saris Gerjo JVM van Osch Laura B Creemers 《Arthritis research & therapy》2014,16(5)