A Comparison of Plasma Testosterone and Progesterone Levels in The Thredbo and Duckmaloi River Platypuses Over a Twelve Month Cycle.

Abstract

A 1-2 ml blood sample was removed from the bill sinus of 208 captured platypuses from the Duckmaloi and Thredbo Rivers over the period January 1991-March 1993. Platypuses from the Duckmaloi were sampled monthly during 1992 and in February, August and December from the Thredbo River in the same year. The numbers and sex of platypuses sampled are recorded in the following Table. Samples were stored on ice and plasma separated from blood cells within 24 hours of sampling by centrifugation for I0 minutes and the supernatant stored at -20°C. The changes in plasma testosterone and progesterone for platypuses from both rivers were compared over a 12 month cycle. The levels of these two hormones were considerably less in the breeding season in the Thredbo River platypuses than in those from the Duckmaloi River. Peak plasma progesterone levels of the order of 90 ng/ml were measured in the Duckmaloi River females compared to levels of <5 ng/ml in Thredbo River females. Male plasma testosterone levels in animals from the Duckmaloi River peaked around 15 ng/ml, whereas Thredbo River males had levels of around 6 ng/mI. These data suggest that over the period of the two year study, platypus breeding potential in the Thredbo River was significantly impaired.