Browsing by Author "Dabee, Vidushi Prema"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Open Access
    Comparison of the long bone microstructure of two southern African marine birds, the Cape gannet (Morus capensis) and the African penguin (Spheniscus demersus) with respect to their aquatic adaptations
    (2013) Dabee, Vidushi Prema; Chinsamy-Turan, Anusuya; Canoville, Aurore
    The Cape gannet (Morus capensis) and the African penguin (Spheniscus demersus) have distinct aquatic adaptations for locomotion. The gannet, which is an efficient flying bird, uses both fore- and hind limbs to propel itself under water. On the other hand, the flightless penguin swims underwater using only its forelimbs. In this study, the long bones of ten penguins and nine gannets were compared in terms of microanatomy and histology with respect to ontogenetic stage (hatchlings, juveniles and adults) and locomotion. Micronatomical and histological findings of the fore-limbs and hind limbs show that the bone microstructure of the gannets and the penguins differs significantly in term of compactness and bone remodelling. Penguin bones are more thick-walled and compact as compared to gannet bones and their cortical tissue is dominated by simple vascular canals whilst the medullary cavity is nearly absent. The forelimb bones of penguins are more compact that the hind limb bones. This is due to the aquatic adaptation of the bone to fore-limb underwater propulsion. On the other hand, the gannet bones are thin walled, less compact with primary osteons dominating the mid-cortex, and a large vacant medullary cavity is present. The gannet fore- and hind limb bones do not differ in terms of bone compactness. Ontogenetic differences in the penguin long bones show that the hatchling bears an active growth phase. Some of the bones of the juvenile penguins are still actively growing whilst the adult ones appear to have stopped growing as the bone mid-cortex is more organized. For the gannet species, the juvenile and adult differs in terms of the presence and thickness of the inner and outer circumferential layers and the presence of circumferential vascularizations. Intra-specific differences are noted in the juvenile penguins with one specimen still undergoing active growth depicted by the presence of numerous simple vascular canals. Amongst the adult penguins, one male specimen is actively molting as indicated by the presence of large resorption cavities in all of the long bones. One adult gannet individual possesses large resorption cavities in all its long bones as a result of starvation caused by perforation of its intestines. Inter-skeletal differences are noted with the stylopod and zeugopod being the most affected by sub-aquatic locomotion with osteosclerosis occurring the most in the proximal bone and decreases in the distal bones going from the pectoral to the pelvic bones in the African penguin. In the Cape gannet, the stylopod and ulna have micro-structural features for torsional resistance during flight.
  • Thumbnail Image
    Item
    Open Access
    Life cycle and host preferences in the Agapanthus borer (Neuranethes spodopterodes)
    (2013) Dabee, Vidushi Prema; Picker, Mike
    The species Neuranethes spodopterodes is a pest of the Agapanthus species. The larva feeds gregariously on the leaves and rhizomes and cause extensive damage to the plant. This study shows the N.spodopterodes have 6 larval instars. The use of the head capsule width as a morphometric parameter and applying it to Dyar's rule gives significant results which allow for adequate determination of the larval instar. The Agapanthus borer has a life cycle that last approximately 84 days. Some species of Agapanthus are the preferred host plant for oviposition by the female N.spodopterodes. Agapanthus inapertus, Agapanthus caulescens and Agapanthus praecox are the most infested with the Agapanthus borer eggs. Leaf sizes do not appear to be a factor that influences the female choice. There appears to be no preference from the larva during feeding. The larva fed equally on all the six Agapanthus species including A. africanus (p>0.05). This shows that the chemical composition of these species is closely related. Since the larva has no feeding preference, this reinforces the fact that it is the female moth that chooses the host plant and that it abides with preference-performance hypothesis. Since A. africanus is subjected to feeding by the larva under laboratory conditions, it could potential imply that in the event of a range shift by the gravid female, that this species of plant is at risk of extinction. The presence of a parasitoid wasp, Trichogramma in the egg of N. spodopterodes and that the level of parasitism is about 86% suggests that this parasitoid could potentially be used as a biological control agent of the Agapanthus borer.