A comparison of seasonal changes in the concentrations of androgens in the peripheral blood of wild and domestic ducks

Abstract

Blood samples taken in monthly intervals over a 2-year period from individually marked wild mallard and Khaki Campbell drakes were assayed for testosterone (T) and 5α-dihydrotestosterone (DHT). In the first year plasma T and DHT were measured simultaneously using a competitive protein binding (CPB) method, while in the second year T (without separation from DHT) was determined with a commercial radioimmunoassay (RIA). The wild mallard drakes showed a bimodal pattern in the annual variation of the T concentrations, one peak coinciding with the reproductive season and the second in autumn. The Khaki Campbell drakes had high T levels in spring, late summer, and in autumn/winter. In some of these birds the depression of the T concentrations usually observed in June and/or July was only slight. In both wild and domestic drakes plasma T and LH concentraitons were linearly correlated. The late autumnal peak of these hormones was not accompanied by an increase in testis weight, in neither wild nor domestic drakes. This peak seems to be related to pair formation. The plasma DHT concentrations of our drakes were higher than those known for mammals. The patterns of the seasonal variations were similar to those of the respective T concentrations. Domestication seems to flatten the seasonal fluctuations of the hormones studied. Maximal values of plasma DHT as well as of plasma LH concentrations were similar in wild and domestic drakes, but in their maximal T levels the domestic drakes by far exceeded the wild ancestor.