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.     

Observations on the histochemistry and ultrastructure of regenerating caudal epidermis of the tuatara Sphenodon punctatus (Sphenodontida,Lepidosauria, Reptilia)

Study of the histology, histochemistry, and fine structure of caudal epidermal regeneration in Sphenodon punctatus through restoration of a scaled form reveals that the processes involved resemble those known in lizards. Following establishment of a wound epithelium (WE), subjacent scale neogenesis involves epidermal downgrowths into the dermis. Although the process is extremely slow, and most new scales do not overlap, their epidermal coverings reestablish epidermal generation (EG) formation. As in lizards, the flat, alpha-keratogenic, WE cells contain lipids as revealed by their affinity for Sudan III. A few mucous cells that store large PAS-positive mucus-like granules also occur in WE. During differentiation of WE cells, among the bundles of 70-nm tonofilaments are many lamellar bodies (LBs) and mucous granules (MGs) that discharge their contents into the cytoplasm and extracellular spaces producing a strongly PAS-positive keratinized tissue. Richness of epidermal lipids coexistent with mucus is a primitive characteristic for amniote vertebrates, probably related to functions as a barrier to cutaneous water loss (CWL). As scale neogenesis begins, beneath the superficial WE appear 3-5 layers of irregularly shaped cells. These contain tonofilament bundles surrounded by small, round keratohyalin-like granules (KHLGs) and a keratinized matrix with beta-keratin packets and a 3-5-nm thick keratin granulation. This mixture of alpha- and beta-keratogenic capacities resembles that seen in the innermost cells of a normal tuatara epidermal generation. As in the latter, but in contrast to both normal and regenerating lizard epidermis, no definable shedding complex with interdigitating clear layer and oberhautchen cells occurs (Alibardi and Maderson, 2003). The tortuous boundaries, and merging beta-keratin packets, identify subjacent keratinizing cells as precursors of the typical stratified, squamous beta-layer seen in long-term regenerated caudal skin wherein the entire vertical sequence of epidermal layers resembles that of normal scales. The sequence of events in caudal epidermal regeneration in S. punctatus resembles that documented for lizards. Observed differences between posttrauma scale neogenesis and scale embryogenesis are responses to functional problems involved in, respectively, restoring, or forming, a barrier to CWL while accommodating rapid somatic growth.     

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.     

Fine structural observations on the epidermis

Summary In species of Apium, Eryngium and Humulus, the cuticular membrane of the petiole could be resolved into two parts, of which the inner one appeared amorphous and after staining appeared to be penetrated by an electron-dense reticulum, whereas the outer layer showed a lamellate structure consisting of electron-dense and electron-transparent plates, 50–80 Å in thickness. These layers are considered to correspond with the cuticular layer and the cuticle proper, respectively. In species of Abutilon and Rumex the cuticle proper did not exhibit the lamellate structure. In the leaves of Eryngium the outer lamellated structure was present in the cuticle of both young and mature leaves. Both the lamellate and non-lamellate types of the cuticle proper increased in thickness with age of the specimen. The results are discussed in relation to earlier investigations.     

Differential effects of trypsin on the epidermis of Rana catesbeiana

Summary The filamentous cytoskeletons of epidermal cells of the bullfrog (Rana catesbeiana) were investigated by electron microscopy. Following treatment with trypsin, sheets of epithelium were removed from swatches of abdominal skin. Trypsinization produces differential effects on the ultrastructure of the various cell layers. The desmosomes of all layers, except those of the stratum corneum, are split by trypsinization and the resulting desmosomal plaques fastened to tonofilaments are retracted into cells to form deep inpouchings of the plasma membranes, while tonofilament bundles become diffuse. Epidermal sheets were gently homogenized to form a suspension of cell remnants with damaged plasma membranes as indicated by vital dye exclusion tests and electron microscopy. Cytoskeletons retain their shapes, yet the lateral distances between individual tonofilaments within bundles appear to increase, thus forming diffuse lacelike structures. These observations support the suggestion that tonofilament bundles, when fastened to desmosomes, have elastic properties. The possible role of the cytoskeletons in the maintenance of cell size and shape in an ion-transporting epithelium is discussed.This investigation was supported, in part, by United States Public Health Service Training Grant AH 01037-01