Browsing by Author "Detoeuf-Boulade, Audrey Simone"
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- ItemReproductive cycle and sexual size dimorphism of the Nile Crocodile (Crocodylus niloticus) in the Okavango Delta, Botswana(Stellenbosch : Stellenbosch University, 2006-12) Detoeuf-Boulade, Audrey Simone; Laslie, A. J.; Hurter, E.; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: The reproductive cycle of female and male Crocodylus niloticus was investigated in the Okavango Delta, Botswana. Plasma samples collected from crocodiles larger than 110 cm in total length (TL) were analysed for: (i) estradiol-17P (E2), testosterone (T) and progesterone in females, and testosterone in males by means of enzymatic immunoassays (EIA); (ii) vitellogenin (Vtg), by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis; and (iii) triacylglycerol (TAG), total cholesterol (CHO) and phospholipids (PL) by means of calorimetric enzyme assays. In addition, spem1 samples were collected from males larger than 180 cm TL and observed under a microscope for the presence or absence of spermatozoa. Females reach sexual maturity at 230 cm TL. Only 60 % of adult females reproduced each year. Reproductively active females produced plasma vitellogenin during winter and early summer (June-September), when elevated plasma steroid E2 concentrations were detected. Sex steroid hormone concentrations were comparable between reproductively and nonreproductively active females, however they did not follow the same cyclicity. Nonreproductively active females showed elevated hormone concentrations during August instead of Jw1e, and did not produce significant levels of plasma Vtg. One male of 192 cm TL was producing spennatozoa, therefore, male C. niloticus may reach sexual maturity at this size. However this size class may not be able to successfully reproduce because of competition with larger males. Spermatozoa were present in the semen samples from June, when plasma T started rising, throughout October. Plasma T peaked in August during the mating season. Plasma TAG, CHO and PL, neither varied seasonally, nor conelated with seasonal variation in any plasma steroid hormone concentrations or reproductive events either in females or males. Variation in plasma sex steroid hormone and lipid concentrations in different size classes was also investigated. In addition, four body and three head measurements were analysed for Sexual Size Dimorphism (SSD). The head shape of adult males and females differed significantly, males having a broader and shorter head than females. Baseline infommtion on growth form and equations predicting Snout-Vent Length or TL from any trait measurements are also available.