Reproductive biology of the African clawed frog, Xenopus laevis
Everson, Gideon Johannes
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Apart from the mouse, rat, and chicken, the clawed frog, Xenopus laevis, is probably the best-studied chordate laboratory animal. Although this animal has been studied for decades around the world we still know relatively little about its biology, including its reproduction under natural conditions. It is surprising that we know so little about an animal for which the entire genome has been sequenced. The aim of this study was to characterise the reproductive biology of the clawed frog over a period of a year. On a monthly basis, 10 males and 10 females were collected from each of three study sites. Morphometric measurements were taken for all animals. Blood samples were taken, gonads examined at gross morphological level and gonads fixed for histological analysis. Gross morphological anomalies showed prevalence between 2.1 % and 3.8% at the three study sites. Gonads were serially sectioned and the reproductive state of the gonads determined by means of histometric analysis as a function of seasonal changes. Photomicrographs were taken of the gonads under a microscope and the cell types were scored quantitively. The histological sections of the gonads were examined for gonadal anomalies, including testicular oocytes. Testicular oocytes were present at all three study sites with prevalence between 12.5% and 20.2%. Water quality parameters and environmental data were collected at all three sites for the duration of the study. External sex characters of Xenopus laevis were also classified and each individually scored. The age structure of Xenopus laevis populations was also determined at the three study areas. Hormonal analysis was also done to determine the concentrations of sex steroids testosterone and estradiol. The ecological aspects of Xenopus laevis reproduction were also characterise at a fourth study site. Rainfall had the determining effect of Xenopus laevis reproduction. It was also found that the clawed frog had an extended breeding season from August to March.
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