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Search Results: 1 - 10 of 248911 matches for " David P. Jacobus "
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Evolutionary patterns of proteinase activity in attine ant fungus gardens
Tatyana A Semenova, David P Hughes, Jacobus J Boomsma, Morten Schi?tt
BMC Microbiology , 2011, DOI: 10.1186/1471-2180-11-15
Abstract: We determined proteinase activity profiles across a wide pH range for fungus gardens of 14 Panamanian species of fungus-growing ants, representing eight genera. We mapped these activity profiles on an independently obtained molecular phylogeny of the symbionts and show that total proteinase activity in lower attine symbionts peaks at ca. pH 6. The higher attine symbionts that have no known free-living relatives had much higher proteinase activities than the lower attine symbionts. Their total in vitro proteinase activity peaked at pH values around 5, which is close to the pH that the ants maintain in their fungus gardens, suggesting that the pH optimum of fungal proteinases may have changed after the irreversible domestication of evolutionary more derived fungal symbionts. This notion is also supported by buffering capacities of fungus gardens at pH 5.2 being remarkably high, and suggests that the fungal symbiont actively helps to maintain garden acidity at this specific level. Metalloproteinases dominated the activity profiles of lower attine gardens and may thus represent the ancestral type of proteinase production, whereas serine proteinase activity dominated the activity profiles of the higher attine gardens reared by Trachymyrmex and Sericomyrmex, suggesting that there may be trade-offs in the production of these enzyme classes. Remarkably, the single symbiont that is shared by species of the crown group of Atta and Acromyrmex leaf-cutting ants mostly showed metalloproteinase activity, suggesting that recurrent changes in enzyme production may have occurred throughout the domestication history of fungus-garden symbionts.Proteinase pH optima and buffering capacities of fungal symbionts appear to have evolved remarkable adaptations to living in obligate symbiosis with farming ants. Although the functional roles of serine and metalloproteinases in fungus gardens are unknown, the differential production of these classes of proteolytic enzymes suggest that substrate
Disease Dynamics in a Specialized Parasite of Ant Societies
Sandra B. Andersen, Matthew Ferrari, Harry C. Evans, Simon L. Elliot, Jacobus J. Boomsma, David P. Hughes
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0036352
Abstract: Coevolution between ant colonies and their rare specialized parasites are intriguing, because lethal infections of workers may correspond to tolerable chronic diseases of colonies, but the parasite adaptations that allow stable coexistence with ants are virtually unknown. We explore the trade-offs experienced by Ophiocordyceps parasites manipulating ants into dying in nearby graveyards. We used field data from Brazil and Thailand to parameterize and fit a model for the growth rate of graveyards. We show that parasite pressure is much lower than the abundance of ant cadavers suggests and that hyperparasites often castrate Ophiocordyceps. However, once fruiting bodies become sexually mature they appear robust. Such parasite life-history traits are consistent with iteroparity– a reproductive strategy rarely considered in fungi. We discuss how tropical habitats with high biodiversity of hyperparasites and high spore mortality has likely been crucial for the evolution and maintenance of iteroparity in parasites with low dispersal potential.
Graveyards on the Move: The Spatio-Temporal Distribution of Dead Ophiocordyceps-Infected Ants
Maj-Britt Pontoppidan, Winanda Himaman, Nigel L. Hywel-Jones, Jacobus J. Boomsma, David P. Hughes
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0004835
Abstract: Parasites are likely to play an important role in structuring host populations. Many adaptively manipulate host behaviour, so that the extended phenotypes of these parasites and their distributions in space and time are potentially important ecological variables. The fungus Ophiocordyceps unilateralis, which is pan-tropical in distribution, causes infected worker ants to leave their nest and die under leaves in the understory of tropical rainforests. Working in a forest dynamic plot in Southern Thailand we mapped the occurrence of these dead ants by examining every leaf in 1,360 m2 of primary rainforest. We established that high density aggregations exist (up to 26 dead ants/m2), which we coined graveyards. We further established that graveyards are patchily distributed in a landscape with no or very few O. unilateralis-killed ants. At some, but not all, spatial scales of analysis the density of dead ants correlated with temperature, humidity and vegetation cover. Remarkably, having found 2243 dead ants inside graveyards we only found 2 live ants of the principal host, ant Camponotus leonardi, suggesting that foraging host ants actively avoid graveyards. We discovered that the principal host ant builds nests in high canopy and its trails only occasionally descend to the forest floor where infection occurs. We advance the hypothesis that rare descents may be a function of limited canopy access to tree crowns and that resource profitability of such trees is potentially traded off against the risk of losing workers due to infection when forest floor trails are the only access routes. Our work underscores the need for an integrative approach that recognises multiple facets of parasitism, such as their extended phenotypes.
Behavioral mechanisms and morphological symptoms of zombie ants dying from fungal infection
David P Hughes, Sandra B Andersen, Nigel L Hywel-Jones, Winanda Himaman, Johan Billen, Jacobus J Boomsma
BMC Ecology , 2011, DOI: 10.1186/1472-6785-11-13
Abstract: We found that infected ants behave as zombies and display predictable stereotypical behaviors of random rather than directional walking, and of repeated convulsions that make them fall down and thus precludes returning to the canopy. Transitions from erratic wandering to death grips on a leaf vein were abrupt and synchronized around solar noon. We show that the mandibles of ants penetrate deeply into vein tissue and that this is accompanied by extensive atrophy of the mandibular muscles. This lock-jaw means the ant will remain attached to the leaf after death. We further present histological data to show that a high density of single celled stages of the parasite within the head capsule of dying ants are likely to be responsible for this muscular atrophy.Extended phenotypes in ants induced by fungal infections are a complex example of behavioral manipulation requiring coordinated changes of host behavior and morphology. Future work should address the genetic basis of such extended phenotypes.Some parasites can adaptively take over and completely control the behavior of their hosts leading to positive fitness returns for parasite genes [1-4]. Host behavior is an extended phenotype of the parasite [5]. The degree of behavioral manipulation varies greatly across parasites from very slight alterations of pre-existing behaviors [6] to the expression of wholly novel behaviors that are never seen in healthy hosts [7]. Extended phenotypes have gained considerable prominence in community- [8], evolutionary- [9] and behavioral ecology [10].Early studies of extended phenotypes focused on detailing behavioral changes and inferring whether they represent adaptations for parasites or should rather be interpreted as adaptive defense mechanisms of the host or as by-products of infection [11-13]. Recently, more integrative approaches have emerged which includes a greater focus on the mechanisms by which behavioral changes occur. An important component is a fuller understanding of th
Calvin and mission
Jacobus (Kobus) P. Labuschagne
HTS Theological Studies/Teologiese Studies , 2009, DOI: 10.4102/hts.v65i1.310
Abstract: It has often been stated or implied that John Calvin and the Reformers in general were indifferent to or even against mission. The aim of this study is to point out that this understanding is not a true version of the facts. A thorough examination of the theology and actions of John Calvin, evaluated against the background of his times and world, reveals that he was firmly committed to spreading the Gospel of Jesus Christ, the Lord. Also the theological insights of Calvin and the Reformers not only provided the crucial theological basis to support the future massive missionary expansion of Protestant churches, but necessitate for all times Church mission as a sure consequence of their theology. Calvin’s theology can indeed be described as an ‘essentially missionary theology’. In the heart of Calvin’s theological thinking clearly features the doctrine of justifi cation – because medieval man’s concern for salvation needed to be answered. How to cite this article: Labuschagne, J.P., 2009, ‘Calvin and mission’, HTS Teologiese/Theological Studies 65(1), Art. #310, 8 pages. DOI: 10.4102/hts.v65i1.310
A Late Eocene age proposal for the Loreto Formation (Brunswick Peninsula, southernmost Chile), based on fossil cartilaginous fishes, paleobotany and radiometric evidence
Otero,Rodrigo A; Torres,Teresa; Le Roux,Jacobus P; Hervé,Francisco; Fanning,C. Mark; Yury-Yá?ez,Roberto E; Rubilar-Rogers,David;
Andean geology , 2012,
Abstract: we present new data on the paleoichthyology, paleobotany and radiometric results of the loreto formation in the brunswick peninsula of southernmost chile, that allow us to propose a late eocene age. the rich diversity of fossil cartilaginous fishes (chondrichthyes, elasmobranchii) recognized in upper levels of this unit includes the taxa carcharías aff. 'hopef (agassiz), odontaspis sp., carcharoides catticus (philippi), striatolamia macrota (agassiz), anomotodon sp., macrorhizoduspraecursor (leriche), galeorhinus sp., abdounia sp., hexanchus sp., squatina sp., hexanchidae indet.,myliobatis sp., myliobatoidea indet., and ischyodus dolloi leriche. this assemblage has clear ecological affinities with eocene tethyan fauna previously described in the northern hemisphere, and also has common elements with eocene cartilaginous fishes from antarctica. additionally, a paleobotanic study of this unit identified leaf imprints ofasplenium sp., pteris sp., podocarpus sp., and abundant angiosperms including nothofagus lanceolata dusén, n. simplicidens dusén, n. variabilis dusén, n. cf. alessandri espinosa, n. subferruginea (dusén), hydrangea sp. and phyllites spp. wood remains of nothofagoxylon scalariforme gothan and araucariaceae cf. araucarioxylon kraus were also identified. additionally, pollen grains indicate gymnosperms and angiosperms: podocarpidites otagoensis couper, retitricolpites sp., tricolpites sp., liliacidites sp., polyporina sp., nothofagidites cincta cookson, and nothofagidites cranwellae couper, having affinities with eocene florae, and being consistent with the age of the fossil fishes. finally, a shrimp u-th-pb analysis of two samples collected from the studied beds provided thirty-eight and sixty zircon grains, indicating a clear main peak at 36.48±0.47 ma (mswd=1.5) and 36,73±0.50 ma (mswd=0.65). the integrated results indicate that the upper part of the loreto formation has a minimum priabonian age, supporting previous reassignations of this part of the fo
Novel Triazine JPC-2067-B Inhibits Toxoplasma gondii In Vitro and In Vivo
Ernest J. Mui,Guy A. Schiehser,Wilbur K. Milhous,Honghue Hsu,Craig W. Roberts,Michael Kirisits,Stephen Muench,David Rice,J. P. Dubey,Joseph W. Fowble,Pradipsinh K. Rathod,Sherry F. Queener,Susan R. Liu,David P. Jacobus,Rima McLeod
PLOS Neglected Tropical Diseases , 2008, DOI: 10.1371/journal.pntd.0000190
Abstract: Background and Methodology Toxoplasma gondii causes substantial morbidity, mortality, and costs for healthcare in the developed and developing world. Current medicines are not well tolerated and cause hypersensitivity reactions. The dihydrotriazine JPC-2067-B (4, 6-diamino-1, 2-dihydro-2, 2-dimethyl-1-(3′(2-chloro-, 4-trifluoromethoxyphenoxy)propyloxy)-1, 3, 5-triazine), which inhibits dihydrofolate reductase (DHFR), is highly effective against Plasmodium falciparum, Plasmodium vivax, and apicomplexans related to T. gondii. JPC-2067-B is the primary metabolite of the orally active biguanide JPC-2056 1-(3′-(2-chloro-4-trifluoromethoxyphenyl?oxy)propyloxy)- 5-isopropylbiguanide, which is being advanced to clinical trials for malaria. Efficacy of the prodrug JPC-2056 and the active metabolite JPC-2067-B against T. gondii and T. gondii DHFR as well as toxicity toward mammalian cells were tested. Principal Findings and Conclusions Herein, we found that JPC-2067-B is highly effective against T. gondii. We demonstrate that JPC-2067-B inhibits T. gondii growth in culture (IC50 20 nM), inhibits the purified enzyme (IC50 6.5 nM), is more efficacious than pyrimethamine, and is cidal in vitro. JPC-2067-B administered parenterally and the orally administered pro-drug (JPC-2056) are also effective against T. gondii tachyzoites in vivo. A molecular model of T. gondii DHFR-TS complexed with JPC-2067-B was developed. We found that the three main parasite clonal types and isolates from South and Central America, the United States, Canada, China, and Sri Lanka have the same amino acid sequences preserving key binding sites for the triazine. Significance JPC-2056/JPC-2067-B have potential to be more effective and possibly less toxic treatments for toxoplasmosis than currently available medicines.
Sedimentary processes on a Gilbert-type delta in Lake Llanquihue, southern Chile
Rojas,Eduardo; Le Roux,Jacobus P;
Revista geológica de Chile , 2005, DOI: 10.4067/S0716-02082005000100002
Abstract: a small gilbert-type delta on the southern shore of lake llanquihue, southern chile, was studied over a period of two months. bottom samples were taken by scuba diving along a 10 x 10 m grid to determine the distribution of sedimentary facies. the wind direction, wave conditions, underwater current directions and the orientation of sedimentary structures were recorded on a daily basis. observations made during fair-weather conditions indicate that neither waves nor currents have any significant effect on the bottom sediments, and that the only transport is produced by bivalves causing small avalanches on the steep delta slope. this probably prevents the oversteepening and large-scale slope collapse typical of many gilbert deltas. observations recorded from shore during one major storm, show an excellent agreement with wave theory and empirical predictions, indicating that storm waves can affect the whole delta front and slope. these waves break about 35 m from shore where there is a clear transition from clast-supported gravel on the inner delta front to matrix-supported gravel and gravelly sand on the outer front. the storm waves are able to transport cobbles up to 40 cm in diameter. during these events, strong lakeward-directed bottom currents enhanced by the effluent plume of the river, transport some of these clasts to the edge of the delta front, where they avalanche down to the foot of the delta. during the waning stages of the storm and shortly thereafter, dense, sediment-laden bottom currents discharged from the river mouth carry plant material down the delta slope and over the pro-delta, burying the cobbles just deposited. a single cycle of delta progradation should produce two coarsening-upward cycles, which might be confused in the rock record with two distinct phases of delta progradation
Leopard range size and conservation area size in the southern Kalahari
Jacobus du P. Bothma,Marius D. Bothma
Koedoe : African Protected Area Conservation and Science , 2012,
Abstract: The range use patterns of adult leopards were used to examine the impact of environmental quality on conservation area size in the arid south-western portion of the Kgalagadi Transfrontier Park in southern Africa. The ranges of the leopards are the largest recorded in the world, with a mean size of 2104.4 km2 (SEM 995.95 km2 ) for males and 1258.5 km2 (SEM 541.50 km2 ) for females. Overlaps in range use within and between the sexes and the size of this conservation area make it possible to sustain a genetically viable population of leopards in this arid environment.Conservation implications: When establishing conservation areas that contain large carnivores in arid and semi-arid regions, prey abundance and range use should be considered for the area to be able to sustain viable populations of such carnivores. The results emphasise the importance of establishing large transfrontier conservation areas where individual conservation areas are too small to do so. This study is the first to do so for leopards in southern Africa.
(Re)discovering a missional-incarnational ethos
Jacobus Kok,Cornelius J.P. Niemandt
HTS Theological Studies/Teologiese Studies , 2009, DOI: 10.4102/hts.v65i1.274
Abstract: In this article, a few of the elements and dynamics of social movements will be explored. It will be argued that the traditional institutional church is in a critical period in the cycle of movements, where the need for the (re)discovery of our missional-incarnational ethos and the theology of restoration might energise the church to (re)activate the dynamics of movements. The narrative of Jesus and the Samaritan woman in John 4 will be investigated as an example of Jesus’s missionalincarnational ethos and of the relation to a theology of restoration. Finally, some challenges for the church with regard to ecclesiology, spirituality and leadership will be proposed. How to cite this article: Kok, J. & Niemandt, C.J.P., 2009, ‘(Re)discovering a missional-incarnational ethos’, HTS Teologiese Studies/Theological Studies 65(1), Art. #274, 7 pages. DOI: 10.4102/hts.v65i1.274
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