Gait choice in desert-living black-backed jackals

Gait selection is a strategy used by quadrupeds to meet the demands of locomotion under variable environmental conditions. The movement of black-backed jackals Canis mesomelas within a desert area was investigated. The usage and distribution of gaits in three distinct desert environments in the Namib Desert, Namibia, were analysed. The areas were chosen based on topographical differences: a bare, a featureless sand plain in an interdune valley, a large sand dune and a narrow dune valley with clumped plant growth. Fresh jackal tracks were recorded by GPS once a week for 1 year. Gait types, gait segment lengths and the rate of switches between gaits were analysed. Trot was the most frequently used gait in all areas, followed by walk and the two types of gallop. Jackals used faster gaits, with the lowest number of gait switches in the interdune plain. Movements on the sand dune were characterized by shorter gait segment lengths and frequent gait changes. In the dune valley, movements were slower and the rate of gait changes was intermediate between the other two areas. The strongest influence on gait choice and on gait changes was found to be the terrain topography, mainly the grade. Gait and track choice can be seen as a dynamic adaptation to a demanding environment like the Namib Desert.     

Fine structural observations on the epidermis

Summary The organization of the wall of epidermal cells in the petiole of species of Apium, Eryngium, Rumex, and Abutilon as well as that of the epidermis of Avena coleoptile has been investigated. The outer and inner tangential walls consist of layers in which the cellulose microfibrils are oriented alternately parallel or transverse to the longitudinal cell axis. This organization resembles that previously described for collenchyma cell walls (Wardrop, 1969; Chafe, 1970). On the radial (anticlinal) walls the orientation of the microfibrils is transverse and these appear continuous with the layers of transverse orientation of the outer and inner tangential walls. Variation in thickness of the outer tangential, and radial, and inner tangential walls appears to result from the variation in thickness of those layers in which the microfibrils have a longitudinal orientation. The extent to which these observations can interpreted in terms of some type of modified multi-net growth is discussed.