Browsing by Author "Van Wyk, J. H."
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- ItemThe morphological and physiological changes during the reproductive cycle of the female rock lizard, Agama atra Daudin, 1802(Stellenbosch : Stellenbosch University, 1982-12) Van Wyk, J. H.; Veith, W. J.; Morgenthal, J. C.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Morphological and physiological changes during the annual reproductive cycle of the female oviparous lizard, Agarna atra, are described. 1 • 2. 3. 4. 5. 6. 7. 8. The onset of the breeding cycle was marked by vitellogenic ovarian hyper= trophy (September) and ovulation of the first clutch occurred in c;x:tober, after which a second clutch was produced. During February no vitellogenic females were collected. The onset and tennination of the breeding cycle, correlated with the spring and aufumnal equinox as well as increased and decreased mean monthly air temperatures. Photothennal regimes ( 14L : 10 D and 25 - 45 °C) induced vitellogenesis in females collected during the winter months. Histological changes of the growing oocyte were studied. CXJgonial pro= liferation, oogenesis and folliculogenesis in Agama. atra appeared to be consistant with the general squamate pattern. Post-ovulatory and two types of atretic follicles are described. The fatbody cycle showed an inverse correlation with ovarian hypertrophy. Total plasma cholesterol varied between 200 and 350 -1 mg. 1 OOml • A decrease was correlated with ovarian hypertrophy and fatbody depletion. The total plasma protein concentration decreased during vitellogenesis· and increased before ovulation. The plasma proteins separated into five major fractions upon cellulose acetate electrophoresis. Ovarian hypertrophy was accompanied by an increase in fraction II (similar m::>bility .as human "Beta-globulins"). Fractions V ("albumin"), IV and III ("Alpha-globulins") were conccmitantly decreased. Plasma calcium concentrations increased significantly (P<0.001) during vitellogenesis. A post-ovulator.1 progesterone surge (7450 pg. 0.2ml-1) with the presence of well developed corpora lutea. The onset of a second vitellogenic cycle ~fs evident during relative high prbgesterone levels (1 500 pg. 0.2rill ). ' 9. The oviducal index showed a high correlation with ovarian development, indicating oestrogenic activity. 10. Oestrogen and oestrogen plus progesterone treabnent resulted in increased plasma vitellogenic paramters in the male, Agama atra. Progesterone alone had no effect. 11. Both PMSG and HCG treabnent (4 IU per lizard) induced vitellogenesis in females containing quiescent ovaries, although PMSG was found to be more potent in inducing ovulation. 12. No significant effect of arginine-vasotocin and oxytocin on oviposition could be observed. KEY WORDS: Squamata, Ag3I1la, Female breeding season, environmental, seasonal changes, ovarian histology, fatbody, cholesterol, plasma proteins, calcium, oviduct, progesterone, vitellogenesis, gonadotropins, oviduct contractility.
- ItemReptile fauna of the Katse Dam catchment area and a biogeographical assessment of species composition in the Lesotho Highlands(AOSIS, 1993) Mouton, P. L. F. N.; Van Wyk, J. H.With only seven lizard and five snake species recorded to date, species richness in the catchment area is much lower than expected. Species richness in the western and central districts of the Lesotho Highlands in general is low, emphasising the role of the Drakensberg-Maluti mountain complex as a barrier to species dispersal. The reptile fauna of the western/central highland area is primarily composed of widespread generalist species. The eastern highland areas, on the other hand, have a substantial endemic component, indicating the greater potential of these areas as a conservatory of geographical isolates. The direct impact of the Katse Dam on the local reptile fauna is expected to be minimal. -from Authors
- ItemSoils of South Africa(Open Journal Systems, 2011-10) Hoffman, J. E.; Van Wyk, J. H.Soils of South Africa by Martin Fey. Cambridge University Press, Cape Town (http://cambridge. org). 2010. Pp. 287. Price R225. Hardback, ISBN 978 1107 000 506. This is the first book in 70 years on soils of South Africa and is a significant scientific contribution on the understanding of South African soils. As the title suggests, this book’s main objective is to give the reader a comprehensive view on the unique soils of South Africa, their distribution, properties, classification, genesis and land use. The author has developed his own grouping system with which all the soils from the SouthAfrican soil classification system are grouped into fourteen distinctive soil groups. This totally new concept for South African soils and the key on how to do this is well thought out. This book compares well with any book written in the U.S.A. or Europe and is quite unique in the way the author strikes a relationship between animals and soils. There have been no previous attempts in the literature to illustrate the contribution of animals to soil formation so clearly as this book.