PM15 Biomarkers
Exhibit Hall
8:00 AM - Monday
(PM243) Seasonal changes and natural variability of plasma sex steroid concentrations in Xenopus laevis from South Africa.
Giesy, J.1, du Preez, L.2, Murphy, M.1, Jones, P.1, Solomon, K.3, van der Kraak, G.3, Smith, E.4, Kendall, R.4, Hecker, M.1, 1 Michigan State University, East Lansing, Michigan, USA2 Potchefstroom University for CHE, Potchefstroom, South Africa3 University of Guelph, Guelph, Ontario, USA4 Texas Tech University, Lubbock, Texas, USA
ABSTRACT- Previous investigations of reproductive parameters such as plasma sex steroid concentrations in Xenopus leavis from both the wild and the laboratory have exhibited relatively great variabilities among individuals from a single population. Xenopus laevis have an extended breeding period but physiological processes related to reproduction also undergo distinct seasonal changes, making it often difficult to directly compare results from different studies. This study was designed to measure concentrations of plasma steroid hormones in male and female X. laevis at several times during the reproductive cycle between May and December 2003 in order to better understand the reproductive physiology and associated variabilties in that occur under natural conditions. Adult African clawed frogs of both sexes were collected at 7 different times during the reproductive season from three different locations in the Potchefstrom region, South Africa. Frogs were analyzed for parameters such as gonad growth and plasma sex steroid hormones (testosterone and estradiol). GSI in frogs of both sexes increased steadily during the sampling period. The greatest GSIs in males were 23 +/- 0.02% (mean +/- SEM), 22 +/- 0.02%, and 25 +/- 0.03%, and occurred at all three sites during late October. In females the maximum GSI values were reached in October and November with values reaching from 4.1 +/- 0.8% (site b) to 8.4 +/- 1.2% (site a). This indicates that reproductive activities peak at the end of the year.
Key words: sex steroids, amphibians, natural variability, season