Browsing by Author "Urasa, Felister Manasseh"

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    A comparative study on some aspects of the structural adaptations to burrowing in the rodents Tachyoryctes Splendens (Rhizomyidae) and Tatera Robusta (Cricetidae)
    (University of Dar es Salaam, 1982) Urasa, Felister Manasseh
    A comparative study of some aspects of the skeletal and muscular systems and the integument was conducted in the rodents Tachyoryctes splendens, a fossorial chisel-tooth digger and Tatera robusta a necturnal semi-fossorial scratch digger. Features of Arrvicanthis niloticus a non-burrowing rodent were included for comparison. Selected groups of muscles were dissected out, and the weight of an individual muscle was expressed as a percentage of the weight of the group in which it belonged. T. splendens exhibited the following modifications: Large incisors for digging, a heavily build skull with large squamosal bones and well-developed supraoccipital and sagittal crests. These bones provide firm and extensive attachments for the greatly enlarged Temporalis muscle which is involved in digging. The prominent suproocipital crest also provides strong attachment for the Splenius and cleidomastodeus muscles which turn and raise the head. The Coronoid processes of the mandible on which the Remporalis muscles attach, are higher than the condylar processes, thus increasing the mechanical effect of the muscle on the incisor tip. Other modifications in T. splendens include: a long clecranon process on which the Triceps muscle inserts, slightly heavier digit flexors of the palm and pes than in the other two species, in particular the Flexor digitorum profunds superficial head, Flexor digitorum sublimis, Plantaris, Flexores hallucis and digitorum longus and Tibialis posterior muscles. Also the Caudo-femoralis muscle is heavier and wider in T. splendens than in the other two species in this study. These muscles enhance the strenghth available for collecting the loosened soil, transporting it along the tunnel and kicking it out of the burrow. Eccrine glands are absent on the palms and soles of T. splendens which digs with its teeth in relatively moist soil and spends most of its time underground. They are well developed on the palms of T. robusta where their secretion increases static friction between the dry sandy particles and the palms while digging. Thus T. splendens shows considerable structural modification of the skeleton and muscles of the head in particular Temporalis muscles to suit its mode of digging. Apart from the long sharp claws of the forelimbs, T. robusta does not exhibit other obvious modifications of the skeleto-muscular system to its mode of scratch-digging. Many other modifications seen in fossorial mammals such as reduced eyes and pinnae are in contrast enlarge in T. robusta as an adaptation to living in open areas with little cover.
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    The significance of Calcium and Phosphate in ovarian maturation in the teleost fish Oreochromis Mossambicus.
    (University of Dar es Salaam, 1989) Urasa, Felister Manasseh
    The importance of exogenous and endogenous calcium and phosphate for reproduction in Oreochromis mossambicus was studied. Calcium and phosphate are essential for reproduction since most of the yolk proteins in fish as well as in other vertebrates are calcium binding phospholipoproteins. The effects of changing concentrations of calcium and phosphate in the water and the food on ovarian development were investigated. The study included determination of calcium and phosphate concentrations in bone during ovarian development, under normal feeding conditions and when the fish were put on a calcium and/or phosphate deficient diet. It was found that under normal feeding conditions calcium and phosphate were not mobilized from bone during ovarian growth. Neither did the absence of dietary calcium affect bone calcium, probably because the water rather than the food is the main source of calcium for the fish. However, temporary reduction of phosphate from food caused the fish to selectively extract phosphate from bone. This enabled the fish to sustain reproduction during this period, although the interspawning period was lengthened. Thus prolonged phosphate deficiency in the food may be a real limiting factor to oocyte growth. To investigate the role of the corpuscles of Stannius (CS) during reproduction, the effects on the size and the ultrastructure of the CS of different concentrations of calcium and phosphate in water and food were investigated. In addition the glands were studied in relation to sexual maturation and plasma calcium levels. Increasing Ca2+ concentration in the water increased the size of the CS. Changes in the calcium concentration of the food had no effect on the CS. High phosphate concentrations in the water did not influence the activity of the CS although a slight hyperphosphatemia was induced. Phosphate deficient food caused a slight hypophosphatemia but had no effects on the CS. Thus, there was no evidence for direct involvement of the CS in the control of phosphate metabolism. In sexually mature female fish, CS were larger than in males, and the size increased modestly with ovarian growth. Total plasma calcium was significantly higher in breeding female fish than in males. This was mainly caused by an increase in the non-filtrable calcium fraction, representing protein-bound calcium. It was suggested that activation of CS during ovarian development in females was a response to prevent the rise of the ultrafiltrable calcium fraction. This is a physiologically very important fraction since it consists mainly of ionic calcium. The ultrastructure of the gonadotropic cells was studied during ovarian growth, after ovariectomy and in different concentrations of calcium and phosphate in water and food. The granular endoplasmic reticulum was greatly dilated to form large "vacuoles". The vacuoles were more frequently observed in fish with large ovaries than in fish with small ovaries. In ovariectomized fish, the cytoplasm of the gonadotropes was dominated by vacuoles and was heavily degranulated. In the cytoplasm of some cells, dark electron dense rod-like crystals were observed. No solid evidence was found during the present study to suggest two types of gonadotropic cells in the pituitary of O. mossambicus. The cells did not respond to changes in the calcium or phosphate concentrations of the ambient water or the food.