Abstract:
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.
