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1.
Free-living juvenile Florida scrub-jays, Aphelocoma coerulescens, learned to forage in a novel patch (the centre of a ring) when in proximity to other family members that foraged successfully. We were able to distinguish the contributions of social learning and of individual learning, and to show that social learning occurred. The foraging task required individual jays to dig for peanut bits (chopped fragments) buried in sand in the centre of a 33-cm plastic ring. Jays were trained in their family groups to perform the task during a summer season, and were allowed to perform the task in the presence of juveniles (aged 40-85 days) in later years. Jays living in 18 control families received partial exposure to the training situation, but received no exposure to the ring before being presented with the task in the presence of their young. Juveniles in 16 families with trained jays were able to witness demonstrations and to scrounge peanut pieces from the models as they completed the task. These 41 juveniles learned more of the task than the 33 juveniles in control families. Seven juvenile jays and two older, nonbreeding jays in the trained families completed the task at least once, whereas no jays in control families completed the task. A modified task that prevented snatching also prevented transmission of the complete task, although the 22 juveniles that observed the modified task learned more of the task than the 33 control juveniles. Further analysis indicated that demonstrations had their greatest effect in increasing the probability that juveniles would enter the ring. Copyright 2000 The Association for the Study of Animal Behaviour. 相似文献
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MARIA E. MCNAMARA PATRICK J. ORR TOM MANZOCCHI LUIS ALCALÁ PERE ANADÓN ENRIQUE PEÑALVER 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2012,45(2):210-226
McNamara, M.E., Orr, P.J., Manzocchi, T., Alcalá, L., Anadón, P. & Peñalver, E. 2011: Biological controls upon the physical taphonomy of exceptionally preserved salamanders from the Miocene of Rubielos de Mora, northeast Spain. Lethaia, Vol. 45, pp. 210–226. The middle Miocene Rubielos de Mora Konservat‐Lagerstätte of northeast Spain is hosted within profundal, finely laminated, lacustrine mudstones. The diverse biota includes abundant salamanders. Most individuals died during separate episodes and sank rapidly postmortem. Specimens are typically preserved in dorso‐ventral aspect, the most hydrodynamically stable orientation. The near‐cylindrical morphology of the body, however, allowed some carcasses to settle in or subsequently re‐orientate into, lateral orientations. Loss of skeletal elements (i.e. reduced completeness) reflects their location within the body and followed a distal to proximal trend. Two stages are identified: initial loss of a small number of phalanges, followed by loss of more proximal limb bones plus additional phalanges. Disarticulation is more complex: it occurred via several mechanisms (notably, abdominal rupture and re‐orientation of part of the body and limbs during decay) and shows no consistent pattern among specimens. The physical taphonomy of the salamanders is controlled predominantly by intrinsic biological factors, i.e. the geometry of the body and of individual skeletal elements, the orientation, inherent strength and location of specific joints and the extent to which soft tissues, particularly the skin, persist during decay. These biological factors probably control patterns of physical taphonomy of other fossil tetrapods with a similar skeletal configuration. □Articulation, completeness, Konservat‐Lagerstätten, orientation, quantitative taphonomy, salamanders. 相似文献
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Steve Horvath Abu NM Nazmul-Hossain Rodney PE Pollard Frans GM Kroese Arjan Vissink Cees GM Kallenberg Fred KL Spijkervet Hendrika Bootsma Sara A Michie Sven U Gorr Ammon B Peck Chaochao Cai Hui Zhou David TW Wong 《Arthritis research & therapy》2012,14(6):1-13
Bone tissue has an exceptional quality to regenerate to native tissue in response to injury. However, the fracture repair process requires mechanical stability or a viable biological microenvironment or both to ensure successful healing to native tissue. An improved understanding of the molecular and cellular events that occur during bone repair and remodeling has led to the development of biologic agents that can augment the biological microenvironment and enhance bone repair. Orthobiologics, including stem cells, osteoinductive growth factors, osteoconductive matrices, and anabolic agents, are available clinically for accelerating fracture repair and treatment of compromised bone repair situations like delayed unions and nonunions. Preclinical and clinical studies using biologic agents like recombinant bone morphogenetic proteins have demonstrated an efficacy similar or better than that of autologous bone graft in acute fracture healing. A lack of standardized outcome measures for comparison of biologic agents in clinical fracture repair trials, frequent off-label use, and a limited understanding of the biological activity of these agents at the bone repair site have limited their efficacy in clinical applications. 相似文献
4.
G Y Wu V Keegan-Rogers S Franklin S Midford C H Wu 《The Journal of biological chemistry》1988,263(10):4719-4723
We present evidence that normal hepatocytes can be specifically protected from galactosamine toxicity in vitro by targeting an antagonist to these cells via receptor-mediated endocytosis. The strategy is based upon the following principles: 1) galactosamine is a highly selective hepatotoxin that causes a dose-dependent depletion of uridine intermediates; 2) galactosamine toxicity can be antagonized by supplemental administration of uridine; 3) normal hepatocytes possess unique cell-surface receptors that can internalize galactose terminal (asialo-)glycoproteins with subsequent degradation of the glycoprotein ligand. Based on these facts, we hypothesized that chemical coupling of a galactosamine antagonist to an asialoglycoprotein could result in cell-specific delivery and protection of normal hepatocytes by targeting the antagonist via asialoglycoprotein receptors. Using a model system consisting of freshly isolated rat hepatocytes (receptor (+)) and Morris 7777 rat hepatoma (receptor (-)) cells, sensitivity to galactosamine in vitro was determined and found to be similar for both types of cells. A targetable antagonist was synthesized by coupling uridine monophosphate to asialoorosomucoid in a molar ratio of 5 to 1. Exposure of Morris 7777 cells to the targetable antagonist in the presence of a toxic concentration of galactosamine did not protect these cells as evidenced by a steady decline in the number of viable cells in a fashion identical to cells treated with galactosamine alone. However, normal hepatocytes that received the conjugate in the presence of galactosamine were protected as their viable cell number remained the same as control (untreated) cells. Competition by an excess of asialoglycoprotein inhibited the protective effect of the conjugate, supporting the concept that the asialoglycoprotein component of the conjugate was responsible for the specific delivery of the antagonist to the target cells. 相似文献
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Eight Danish Holstein cows were milked with a 1-mm thick specially designed soft liner on their right rear teat and a standard
liner mounted under extra high tension on their left rear teat. Four of the animals were overmilked for 5 min. Rear teats
were subjected to ultrasound examination on the first day and to infrared thermography on the second day. Teats were submersed
in ethanol 20 min post-milking on the second day. Ultrasonography measurements showed that teat canal length increased by
30–41% during milking. Twenty minutes after milking, teats milked with modified standard liners still had elongated teat canals
while teats milked with the soft liner were normalized. Overmilking tended to increase teat wall thickness. Approximately
80% of variability in teat canal length, from before teat preparation to after milking, could be explained by changes during
teat preparation. Thermography indicated a general drop in teat temperature during teat preparation. Teat temperature increased
during milking and continued to increase until the ethanol challenge induced a significant drop. Temperatures approached pre-challenge
rather than pre-milking temperatures within 10 minutes after challenge. Teat temperatures were dependent on type of liner.
Mid-teat temperatures post-challenge relative to pre-teat preparation were dependent on overmilking. Thermography and ultrasound
were considered useful methods to indirectly and non invasively evaluate teat tissue integrity. 相似文献
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To find out the infection efficiency of recombinant adeno-as sociated virus 2-mediated exogenou s genes in human peripheral blood monocyte-derived dendritic cells(D Cs),the process of transfection wa s investigated by FITC-labeled rAA V2,and observed under confocal mic roscope.Newly separated dendritic cells were tranfected by rAAV2-luc and rAAV2-GFP at different MOI,and transfection efficiency were detec ted by luminometer for rAAV2-luc a nd flow cytometry for rAAV2-GFP.Th e results were elucidated in four different assay systems:(1)60min w as needed for rAAV2 to bind on den dritic cells,and got into cells in the following 10min;(2)the express ion of luc could be detected at th e MOI as low as 1×10~5v.g/cell,and the expression plateau was reached by the MOI of 10~6~10~7v.g/cell,furt her increase of MOI had no functio n on expression level;(3)transgene expression was detected after 48h, and maintained a higher expression level from 96h to 240h after infec tion;(4)7days postinfection of rAA V2-GFP,5%~18% dendritic cells were GFP positive. These data suggest th at rAAV2 vector can efficiently in fect monocyte-derived dendritic ce lls and mediate exogenous gene exp ression,and that the application o f rAAV2 as vector may be useful fo r gene transfer to dendritic cells in ex vivo immunotherapy. 相似文献
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Body condition‐dependent dispersal strategies are common in nature. Although it is obvious that environmental constraints may induce a positive relationship between body condition and dispersal, it is not clear whether positive body conditional dispersal strategies may evolve as a strategy in metapopulations. We have developed an individual‐based simulation model to investigate how body condition–dispersal reaction norms evolve in metapopulations that are characterized by different levels of environmental stochasticity and dispersal mortality. In the model, body condition is related to fecundity and determined either by environmental conditions during juvenile development (adult dispersal) or by those experienced by the mother (natal dispersal). Evolutionarily stable reaction norms strongly depend on metapopulation conditions: positive body condition dependency of dispersal evolved in metapopulation conditions with low levels of dispersal mortality and high levels of environmental stochasticity. Negative body condition‐dependent dispersal evolved in metapopulations with high dispersal mortality and low environmental stochasticity. The latter strategy is responsible for higher dispersal rates under kin competition when dispersal decisions are based on body condition reached at the adult life stage. The evolution of both positive and negative body condition‐dependent dispersal strategies is consequently likely in metapopulations and depends on the prevalent environmental conditions. 相似文献
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THE ROSETTE DISEASE OF PEANUTS (ARACHIS HYPOGAEA L.) 总被引:1,自引:0,他引:1
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An inhibitor of microRNA-122 reduces viral load in chimpanzees that are chronically infected with hepatitis C virus, suggesting
that such an approach might have therapeutic potential in humans. 相似文献