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71.
Jan A. Graf Michael J. Somers Micaela Szykman Gunther Rob Slotow 《Acta theriologica》2009,54(4):333-343
Animal population sizes and trends, as well as their distributions, are essential information to the understanding and conservation
of ecosystems. During this study in Hluhluwe-iMfolozi Park, South Africa, a spotted hyaena Crocuta crocuta Erxleben, 1777 (Hyaenidae) population was surveyed by attracting individuals with pre-recorded sounds. The hyaena population
(excluding cubs) is substantially larger (321 individuals) than the previous estimate of 200 and this population is the second
largest protected population in South Africa. Average hyaena density, at 0.357 individuals/km2, was relatively high compared to other southern African conservation areas, and range from 0 to 1.25 individuals/km2 across sampling stations. For short periods, spatial heterogeneity in density was marked at small and large spatial scales,
but decreased when averaged over a longer period. This heterogeneity may be important in promoting the coexistence of other
large and mobile carnivores in Hluhluwe-iMfolozi Park by creating potential dynamic competition refugia in space and time.
Furthermore, heterogeneity of hyaena density at smaller scales should influence studies investigating the avoidance of hyaenas
by competitively inferior carnivores. 相似文献
72.
73.
PTP1B regulates leptin signal transduction in vivo 总被引:15,自引:0,他引:15
Zabolotny JM Bence-Hanulec KK Stricker-Krongrad A Haj F Wang Y Minokoshi Y Kim YB Elmquist JK Tartaglia LA Kahn BB Neel BG 《Developmental cell》2002,2(4):489-495
Mice lacking the protein-tyrosine phosphatase PTP1B are hypersensitive to insulin and resistant to obesity. However, the molecular basis for resistance to obesity has been unclear. Here we show that PTP1B regulates leptin signaling. In transfection studies, PTP1B dephosphorylates the leptin receptor-associated kinase, Jak2. PTP1B is expressed in hypothalamic regions harboring leptin-responsive neurons. Compared to wild-type littermates, PTP1B(-/-) mice have decreased leptin/body fat ratios, leptin hypersensitivity, and enhanced leptin-induced hypothalamic Stat3 tyrosyl phosphorylation. Gold thioglucose treatment, which ablates leptin-responsive hypothalamic neurons, partially overcomes resistance to obesity in PTP1B(-/-) mice. Our data indicate that PTP1B regulates leptin signaling in vivo, likely by targeting Jak2. PTP1B may be a novel target to treat leptin resistance in obesity. 相似文献
74.
75.
Micaela Martinez-Bakker Kevin M. Bakker Aaron A. King Pejman Rohani 《Proceedings. Biological sciences / The Royal Society》2014,281(1783)
More than a century of ecological studies have demonstrated the importance of demography in shaping spatial and temporal variation in population dynamics. Surprisingly, the impact of seasonal recruitment on infectious disease systems has received much less attention. Here, we present data encompassing 78 years of monthly natality in the USA, and reveal pronounced seasonality in birth rates, with geographical and temporal variation in both the peak birth timing and amplitude. The timing of annual birth pulses followed a latitudinal gradient, with northern states exhibiting spring/summer peaks and southern states exhibiting autumn peaks, a pattern we also observed throughout the Northern Hemisphere. Additionally, the amplitude of United States birth seasonality was more than twofold greater in southern states versus those in the north. Next, we examined the dynamical impact of birth seasonality on childhood disease incidence, using a mechanistic model of measles. Birth seasonality was found to have the potential to alter the magnitude and periodicity of epidemics, with the effect dependent on both birth peak timing and amplitude. In a simulation study, we fitted an susceptible-exposed-infected-recovered model to simulated data, and demonstrated that ignoring birth seasonality can bias the estimation of critical epidemiological parameters. Finally, we carried out statistical inference using historical measles incidence data from New York City. Our analyses did not identify the predicted systematic biases in parameter estimates. This may be owing to the well-known frequency-locking between measles epidemics and seasonal transmission rates, or may arise from substantial uncertainty in multiple model parameters and estimation stochasticity. 相似文献
76.
Kerstin Büchel Nadine Austel Micaela Mayer Jonathan Gershenzon Trevor M. Fenning Torsten Meiners 《BioControl》2014,59(1):29-43
Parasitic insects use herbivore induced plant volatiles as signals for host location. However, their responses to these volatiles in the background of natural habitat odours need further evaluation for developing successful biological control strategies. Field elms (Ulmus minor Miller (Ulmaceae)) release a blend of volatiles in response to oviposition of the elm leaf beetle, Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), a major urban and forest pest in the USA and Australia. This induced blend attracts the beneficial egg parasitoid Oomyzus gallerucae Fonscolombe (Hymenoptera: Eulophidae). Our olfactory assays showed that an odorous background of non-attractive host plant volatiles from feeding damaged elms or (Z)-3-hexenyl acetate masks the attractive effect of the host-induced (E)-β-caryophyllene to O. gallerucae. Quantitative GC–MS analyses revealed decreased concentrations of (Z)-3-hexenyl acetate accompanied by highly increased concentrations of sesquiterpenes in oviposition and feeding treated elms compared to undamaged elms. This finding hints to how the parasitoid might distinguish between different odorous backgrounds. It is corroborated by the outcome of our field study in natural elm stands, where the egg parasitoid parasitized more host egg masses due to an artificially induced blend of elm terpenoids. 相似文献
77.
78.
Micaela Mancini Nadia Woitovich Hugo R. Permingeat Maricel Podio Lorena A. Siena Juan Pablo A. Ortiz Silvina C. Pessino Silvina A. Felitti 《In vitro cellular & developmental biology. Plant》2014,50(4):412-424
The aim of this work was to improve existing transformation protocols and to transform specific genotypes of Paspalum notatum (bahiagrass) for functional analyses of candidate genes involved in reproduction. Three different explants were assayed for in vitro plant regeneration: mature seeds, mature embryos, and shoot meristems. Plant regeneration was achieved with all explant types, but mature seeds produced the optimal rate (78.0%) and were easiest to manipulate. A method based on serial re-induction of calli from meristems of the regenerated lines was also developed, which could be useful in plant breeding strategies pursuing somaclonal variation. Transient transformation experiments were performed on calli obtained from mature seeds using a compressed helium gene gun. Transient transformation constructs included anthocyanin-synthesis genes cloned under the CAMV 35S promoter and an enhanced green fluorescent protein gene (egfp) driven by the rice actin1 (act1) promoter. Selection curves for ammonium glufosinate were developed in order to determine the optimal selective pressure for stable transformation (1.0 mg/L). Stable co-transformation experiments were carried out with two different constructs containing: (1) the reporter egfp gene cloned under the rice act1 promoter and (2) the selector bar gene driven by the ubiquitin promoter. A total of 27 (64.2%) transgenic plants out of 42 resistant plants analyzed were obtained. The presence of the transgenes in regenerated plants was confirmed by polymerase chain reaction and DNA gel blot analysis. Gene expression was demonstrated by eGFP fluorescence detection and in vivo assays for ammonium glufosinate tolerance. This platform is being used to generate transgenic plants of P. notatum to analyze the function of apomixis-associated candidate genes. 相似文献
79.
M. Carmen Martínez-Ballesta Luis López-Pérez Mercedes Hernández Carmen López-Berenguer Nieves Fernández-García Micaela Carvajal 《Phytochemistry Reviews》2008,7(2):251-260
Phytochemicals in vegetables are known to be responsible for protective effects against many human diseases, including cardiovascular
diseases and different types of cancer. Environmental conditions and physiological factors may modify the amounts of these
compounds present in vegetables and fruits, but also crop management strategies could increase the production of phytochemicals.
Therefore, the effects of mineral nutrition, soil composition and water content on the production of phytochemicals have been
considered in the development of different fertilisation strategies, efficient water management and techniques such as grafting.
Finally, the contents of health-promoting compounds in vegetables and fruits depend both quantitatively and qualitatively
on their genetic bases. Thus, conventional breeding and genetic modification have been developed as new methodologies to enhance
the nutritional properties of plants.
M. C. Martínez-Ballesta, L. López-Pérez, M. Hernández, C. López-Berenguer, N. Fernández-García contributed equally. 相似文献
80.
As water and nutrient uptake should be related in the response of plants to salinity, the aim of this paper is to establish whether or not aquaporin functionality is related to H+ -ATPase activity in root cells of pepper ( Capsicum annuum L.) plants. Thus, H+ -ATPase activity was measured in plasma membrane vesicles isolated from roots and aquaporin functionality was measured using a cell pressure probe in intact roots. Salinity was applied as 60 m M NaCl or 60 m M KCl, to determine which ion (Na+ , K+ or Cl− ) is producing the effects. We also investigated whether the effects of both salts were ameliorated by Ca2+ . Similar results were obtained for cell hydraulic conductivity, Lpc , and H+ -ATPase activity, large reductions in the presence at NaCl or KCl and an ameliorative effect of Ca2+ . However, fusicoccin (an activator of H+ -ATPase) did not alter osmotic water permeability of protoplasts isolated from roots. Addition of Hg2+ inhibited both ATPase and aquaporins, but ATPase also contains Hg-binding sites. Therefore, the results indicate that H+ -ATPase and aquaporin activities may not be related in pepper plants. 相似文献