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81.
ABSTRACT. We used a photoactivatable fluid-phase marker to isolate a new collection of thermosensitive endocytosis mutants in the cellular slime mold Dicfyostelium discoideum. All the strains were thermosensitive for growth on bacteria or axenic medium at 27° C. Initial rates of endocytosis rapidly decreased upon incubation at the restrictive temperature, but surprisingly most of the strains showed a transient recovery of activity with prolonged exposure to 27° C. Endocytosis and exocytosis activities were uncoupled for some of the cell lines at 27° C whereas the others had to be shifted to 29° C. Further molecular analysis of these mutants could lead to the discovery of new proteins involved in endocytosis and its regulation. 相似文献
82.
ABSTRACT. In post-embryonic development, the visual system of the cricket Nemobius sylvestris (Bosc) shows a regular increase in the length and number of the ommatidia and a decrease of inter-ommatidial angle so that the adult's is a third of the value in the first larval instar. Further, a 20° widening of the binocular visual field, in the horizontal plane at least, and a three-fold increase of the inter-ocular distance improve the potential for binocular vision. Behavioural experiments showed that the insect orientates with differing precision depending on the distances to targets of constant angular size. Further, in a choice situation between two such vertical targets, the cricket orientates most strongly towards the closer of the two, even at target distances of 52 and 130 cm from its point of decision. In fixed tethered animals, discrimination between a close and a distant target is still possible, but disappears when the head is waxed to the thorax, so that any relative movement between the animal and the object is prevented. As these capabilities exceed the possibilities of binocular triangulation, the possible role of other mechanisms is discussed, particularly that involving movement parallax using both eyes. 相似文献
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ABSTRACT. Orientation towards a rectangular black visual target was measured with tethered crickets, Nemobius sylvestris (Bosc). The orientation reaction was induced only if the target was located in a visual field within 100° of the sagittal plane, 60° above and 40° below the horizontal plane. The motor response was maximum when the target was presented between 30° and 40° of the sagittal plane, and between 0° and 20° above the horizontal one. The orientation reaction was induced optimally by an area of the eye which is lateral and slightly dorsal, whose ommatidia are not included in the binocular field. The ability to move the head enlarged the visual field by about 20° laterally, improving the exploration of the visual space. 相似文献
85.
PIERRE WACHE GERARD MAURICE MICHEL LUCIUS JEAN-FRANCOIS STOLTZ XIONG WANG 《Computer methods in biomechanics and biomedical engineering》2013,16(6):525-533
Abstract Mechanical forces influence endothelial cell's (EC) morphology and functions. In this work it was proposed a numerical analysis of steady laminar flows near a modelled monolayer of elastic ECs in order to determine the local distributions of mechanical forces on the surface and inside the cell. Numerical results showed that the flow induced non uniform mechanical stresses on cell surface and led to a cell deformation. These numerical results were compared with experimental measurements of the deformation of cultured human aortic endothelial cells under flow. It will be interesting to study eventual correlations between the distributions of biological receptors (cytoskeleton, adhesion molecules, etc.) and that of the non-uniform mechanical forces. 相似文献
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JOAQUÍN MECO DANIEL R. MUHS MICHEL FONTUGNE ANTONIO J.G. RAMOS ALEJANDRO LOMOSCHITZ DeANNA PATTERSON 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2011,44(4):440-454
Meco, J., Muhs, D.R., Fontugne, M., Ramos, A.J.G., Lomoschitz, A. & Patterson, D. 2010: Late Pliocene and Quaternary Eurasian locust infestations in the Canary Archipelago. Lethaia, Vol. 44, pp. 440–454. The Canary Archipelago has long been a sensitive location to record climate changes of the past. Interbedded with its basalt lavas are marine deposits from the principal Pleistocene interglacials, as well as aeolian sands with intercalated palaeosols. The palaeosols contain African dust and innumerable relict egg pods of a temperate‐region locust (cf. Dociostaurus maroccanus Thunberg 1815 ). New ecological and stratigraphical information reveals the geological history of locust plagues (or infestations) and their palaeoclimatic significance. Here, we show that the first arrival of the plagues to the Canary Islands from Africa took place near the end of the Pliocene, ca. 3 Ma, and reappeared with immense strength during the middle Late Pleistocene preceding MIS (marine isotope stage) 11 (ca. 420 ka), MIS 5.5 (ca. 125 ka) and probably during other warm interglacials of the late Middle Pleistocene and the Late Pleistocene. During the Early Holocene, locust plagues may have coincided with a brief cool period in the current interglacial. Climatically, locust plagues on the Canaries are a link in the chain of full‐glacial arid–cold climate (calcareous dunes), early interglacial arid–sub‐humid climate (African dust inputs and locust plagues), peak interglacial warm–humid climate (marine deposits with Senegalese fauna), transitional arid–temperate climate (pedogenic calcretes), and again full‐glacial arid–cold climate (calcareous dunes) oscillations. During the principal interglacials of the Pleistocene, the Canary Islands recorded the migrations of warm Senegalese marine faunas to the north, crossing latitudes in the Euro‐African Atlantic. However, this northward marine faunal migration was preceded in the terrestrial realm by interglacial infestations of locusts. □Locust plagues, Canary Islands, Late Pliocene, Pleistocene, Holocene, palaeoclimatology. 相似文献
88.
A carbon-based model is described of the source-sink relationshipsof a stem bearing fruits in space and time and focusing on growthvariability along the branch. The novelty of the model comesfrom the aggregation of physiological processes taking intoaccount spatial aspects. The stem is represented as a set ofcompartments (metamers) connected to source (leafy shoots) andsink (fruits) compartments. Each leafy shoot forms one compartment.The fruit consists of three compartments involved in translocation(cytoplasm), structure (cell wall) and storage (vacuole). Physiologicalprocesses considered are photosynthesis, respiration of fruitsand leaves, translocation of assimilates and fruit growth. Assimilateproduction is regulated by sink strength. Carbon translocationbetween two compartments depends on the gradient of assimilateconcentration. The gradient induces carbon translocation fromthe most to the least concentrated compartment, except for thevacuole compartment into which translocation is possible whateverthe concentration gradient. Fruit growth, in terms of freshweight, results from the phloem water supplied to the fruitaccording to the concentration gradient between the fruit andthe stem. The model is calibrated for peach trees by comparingobserved and simulated fruit dry and fresh weights for a shootwith normal fruit load. The model simulates variability betweenpeach fruits and the effect of contrasting fruit loads. Accordingto this model, photosynthesis increases and assimilate concentrationsin leaves and phloem decrease with decreasing leaf:fruit ratioas reported in the literature. Simulated concentrations of assimilatesin the phloem range from 2 to 14%. Simulated concentration gradientsand specific mass transfer for peach trees range from 0.05 to0.17 g cm-3m-1and from 0 to 3 g cm-2h-1, respectively, and areof the same order of magnitude as those reported for variousother tree species. The model is used to analyse the effectof fruit position relative to the leaves. Copyright 1999 Annalsof Botany Company Peach tree, Prunus persica (L.) Batsch, model, carbohydrates, translocation, source-sink, fruit. 相似文献
89.
This paper contributes to a revision of the genus Halectinosoma . Four new species are described, based on examination of ectinosomatid material from localities in western Europe, eastern Canada and the Arctic. Halectinosoma mandibularis sp. nov. is distinguishable from other species by the reduced setation of the mouthparts and enlarged mandibular gnathobase. Halectinosoma latisetifera sp. nov. bears an affinity with H. cooperatum but is easily distinguished by the shape of the setae on the female fifth leg. A species previously erroneously ascribed to H. finmarchicum (Scott) by several authors is described here as Halectinosoma kliei sp. nov. Halectinosoma gothiceps (Giesbrecht) is redescribed and the closely related Halectinosoma paragothiceps sp. nov. is described and distinguished from H. gothiceps . It is considered likely that some previous records of H. gothiceps are in error. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 149 , 453–475. 相似文献
90.
Processes occurring at the end of the larval stage are of major importance in shaping spatial structure of fish assemblages in coral reefs. However, because of the difficulty in identifying larvae to species, many studies dealing with these stages are limited to the family level. It remains unknown if variation in the spatial structure of coral‐reef fish assemblages across life stages can be detected at such a coarse taxonomic level. Two different surveys conducted in a similar area of New Caledonia, Southwest Pacific, provided the opportunity to compare the structure of coral‐reef fish assemblages collected as pre‐settlement larvae, juveniles and adults along a coast to barrier reef gradient. Adult and juvenile fish were sampled using underwater visual counts (UVC) during the warm seasons of 2004 and 2005. Pre‐settlement larvae were sampled with light‐traps during the same seasons. In order to standardize data between sampling methods, analyses were conducted on the relative abundance (for larvae) and density (for juveniles and adults) of 21 families commonly collected with both methods. Relative abundances/densities of families were analysed as a function of life stage (larvae, juveniles or adults), large‐scale spatial location (coast, lagoon or barrier) and years (2004, 2005) using non‐parametric multidimensional scaling (nMDS) and permutational multivariate analysis of variance (permanova ). Kruskal–Wallis tests were then used to examine differences among life stages and locations for individual families. Different levels of spatial and temporal variability characterized fish assemblages from different life stages, and differences among life stages were detected at all locations and years. Differences among life stages were also significant at the level of individual families. Overall results indicate that studies conducted at the family level may efficiently reveal changes in coral‐reef fish spatial structure among successive life stages when large spatial scales are considered. 相似文献