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Kay Van Damme Petr Benda Dirk Van Damme Peter De Geest Irka Hajdas 《Journal of Natural History》2018,52(31-32):2001-2024
Data on the prehistoric biota of the Socotra Archipelago (Yemen) are scarce. We report on the first extinct vertebrate ever recorded from this western Indian Ocean island group. An exceptionally preserved adult specimen of Egyptian fruit bat Rousettus aegyptiacus was found in a calcite flowstone in Hoq Cave on the NE coast of Socotra Island. Accelerator mass spectrometry (AMS) radiocarbon dating on bone fragments estimates the fossil at ca. 7600–7400 cal a BP (radiocarbon age 6669 ± 70 14C a BP) corresponding to an early Holocene wet period in southern Arabia and the Horn of Africa. Morphometric analysis of the skull compared to Recent specimens from the neighbouring mainlands finds the fossil morphologically most similar to Egyptian (Nile Valley and Libyan Desert), not to East African or Middle Eastern populations. The species is currently absent from the Horn of Africa (Somalia and Eastern Ethiopia). Although potentially a stray individual, we also discuss the palaeoenvironmental implications under the hypothetical scenario that the fruit bat is a remnant of an extinct resident population. If so, the extinction of an important pollinator and seed disperser may have impacted the Socotran terrestrial ecosystems. 相似文献
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Barreto G Schäfer A Marhold J Stach D Swaminathan SK Handa V Döderlein G Maltry N Wu W Lyko F Niehrs C 《Nature》2007,445(7128):671-675
DNA methylation is an epigenetic modification that is essential for gene silencing and genome stability in many organisms. Although methyltransferases that promote DNA methylation are well characterized, the molecular mechanism underlying active DNA demethylation is poorly understood and controversial. Here we show that Gadd45a (growth arrest and DNA-damage-inducible protein 45 alpha), a nuclear protein involved in maintenance of genomic stability, DNA repair and suppression of cell growth, has a key role in active DNA demethylation. Gadd45a overexpression activates methylation-silenced reporter plasmids and promotes global DNA demethylation. Gadd45a knockdown silences gene expression and leads to DNA hypermethylation. During active demethylation of oct4 in Xenopus laevis oocytes, Gadd45a is specifically recruited to the site of demethylation. Active demethylation occurs by DNA repair and Gadd45a interacts with and requires the DNA repair endonuclease XPG. We conclude that Gadd45a relieves epigenetic gene silencing by promoting DNA repair, which erases methylation marks. 相似文献
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Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment 总被引:2,自引:0,他引:2
Scherber C Eisenhauer N Weisser WW Schmid B Voigt W Fischer M Schulze ED Roscher C Weigelt A Allan E Bessler H Bonkowski M Buchmann N Buscot F Clement LW Ebeling A Engels C Halle S Kertscher I Klein AM Koller R König S Kowalski E Kummer V Kuu A Lange M Lauterbach D Middelhoff C Migunova VD Milcu A Müller R Partsch S Petermann JS Renker C Rottstock T Sabais A Scheu S Schumacher J Temperton VM Tscharntke T 《Nature》2010,468(7323):553-556
Biodiversity is rapidly declining, and this may negatively affect ecosystem processes, including economically important ecosystem services. Previous studies have shown that biodiversity has positive effects on organisms and processes across trophic levels. However, only a few studies have so far incorporated an explicit food-web perspective. In an eight-year biodiversity experiment, we studied an unprecedented range of above- and below-ground organisms and multitrophic interactions. A multitrophic data set originating from a single long-term experiment allows mechanistic insights that would not be gained from meta-analysis of different experiments. Here we show that plant diversity effects dampen with increasing trophic level and degree of omnivory. This was true both for abundance and species richness of organisms. Furthermore, we present comprehensive above-ground/below-ground biodiversity food webs. Both above ground and below ground, herbivores responded more strongly to changes in plant diversity than did carnivores or omnivores. Density and richness of carnivorous taxa was independent of vegetation structure. Below-ground responses to plant diversity were consistently weaker than above-ground responses. Responses to increasing plant diversity were generally positive, but were negative for biological invasion, pathogen infestation and hyperparasitism. Our results suggest that plant diversity has strong bottom-up effects on multitrophic interaction networks, with particularly strong effects on lower trophic levels. Effects on higher trophic levels are indirectly mediated through bottom-up trophic cascades. 相似文献
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The additive biclustering model for two-way two-mode object by variable data implies overlapping clusterings of both the objects and the variables together with a weight for each bicluster (i.e., a pair of an object and a variable cluster). In the data analysis, an additive biclustering model is fitted to given data by means of minimizing a least squares loss function. To this end, two alternating least squares algorithms (ALS) may be used: (1) PENCLUS, and (2) Baier’s ALS approach. However, both algorithms suffer from some inherent limitations, which may hamper their performance. As a way out, based on theoretical results regarding optimally designing ALS algorithms, in this paper a new ALS algorithm will be presented. In a simulation study this algorithm will be shown to outperform the existing ALS approaches. 相似文献
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Introduction Curves and surfaces can be represented using coefficients and a set of basis functions[1]. In the following, only curves are considered, but all statements apply equally to surfaces. Different representations use different sets of basis functions. These basis functions can be, for example, polynomials for polynomial curves, Bernstein-polynomials for Bézier curves, or B-spline basis functions for B-spline curves. As long as the general representation is of the form: 0( ) ( )ni i… 相似文献
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Savage DB Agostini M Barroso I Gurnell M Luan J Meirhaeghe A Harding AH Ihrke G Rajanayagam O Soos MA George S Berger D Thomas EL Bell JD Meeran K Ross RJ Vidal-Puig A Wareham NJ O'Rahilly S Chatterjee VK Schafer AJ 《Nature genetics》2002,31(4):379-384
Impaired insulin action is a key feature of type 2 diabetes and is also found, to a more extreme degree, in familial syndromes of insulin resistance. Although inherited susceptibility to insulin resistance may involve the interplay of several genetic loci, no clear examples of interactions among genes have yet been reported. Here we describe a family in which five individuals with severe insulin resistance, but no unaffected family members, were doubly [corrected] heterozygous with respect to frameshift/premature stop mutations in two unlinked genes, PPARG and PPP1R3A these encode peroxisome proliferator activated receptor gamma, which is highly expressed in adipocytes, and protein phosphatase 1, regulatory subunit 3, the muscle-specific regulatory subunit of protein phosphatase 1, which are centrally involved in the regulation of carbohydrate and lipid metabolism, respectively. That mutant molecules primarily involved in either carbohydrate or lipid metabolism can combine to produce a phenotype of extreme insulin resistance provides a model of interactions among genes that may underlie common human metabolic disorders such as type 2 diabetes. 相似文献