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  • Cell intercalation  (1)
  • Dispersal rate  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Tension-dependent collective cell movements in the early gastrula ectoderm of Xenopus laevis embryos (2000)
    Springer
    Development genes and evolution 210 (2000), S. 92-104 
    Details
    ISSN: 1432-041X
    Keywords: Key words Morphogenetic movements ; Mechanical stresses ; Cell intercalation ; Xenopus laevis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Ventral ectodermal explants taken from early gastrula embryos of Xenopus laevis were artificially stretched either by two opposite concentrated forces or by a distributed force applied to the internal explant’s layer. These modes of stretching reflect different mechanical situations taking place in the normal development. Two main types of kinematic response to the applied tensions were detected. First, by 15 min after the onset of concentrated stretching a substantial proportion of the explant’s cells exhibited a concerted movement towards the closest point of the applied stretching force. We define this movement as tensotaxis. Later, under both concentrated and distributed stretching, most of the cell’s trajectories became reoriented perpendicular to the stretching force, and the cells started to intercalate between each other, both horizontally and vertically. This was accompanied by extensive elongation of the outer ectodermal cells and reconstruction of cell-cell contacts. The intercalation movements led first to a considerable reduction in the stretch-induced tensions and then to the formation of peculiar bipolar ”embryoid” shapes. The type and intensity of the morphomechanical responses did not depend upon the orientation of a stretching force in relation to the embryonic axes. We discuss the interactions of the passive and active components in tension-dependent cell movements and their relations to normal morphogenetic events.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004270050015
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Spatial variability of earthworm populations in a permanent polder grassland (1992)
    Springer
    Biology and fertility of soils 14 (1992), S. 260-266 
    Details
    ISSN: 1432-0789
    Keywords: Earthworm activity ; Geostatistics ; Dispersal rate ; Spatial variability ; Land reclamation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary We studied the earthworm distribution in a permanent polder grassland by making two detailed surveys in 1983 and in 1990. Geostatistical procedures were used to investigate the changes in species composition and to determine the dispersal rate. Attention was focused on two soil survey variables closely related to earth-worm distribution, the thickness of the Ah horizon and the number of burrows. The dispersal rate between the two survey dates was 13 m year−1 compared with 10 m year−1 before 1983. The difference was attributed either to the development of new population centres due to dispersal by cow's feet or tractor wheels, this altering the spatial dynamics, or to a lag phase in population development in the years following inoculation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00395461
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    Paper (German National Licenses)
    Fulltext
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