EFFECTS OF LONG-TERM SELECTION FOR BEHAVI OR ON THE LEVEL OF PROGESTERONE IN BLOOD AND ITS CONTENT IN ADRENALS OF SILVER FOX EMBRYOS

The level of progesterone in blood serum and its concentration in adre nals and gonads have been assayed in male and female silver fox embryo s, starting from day 35 of pregnancy for every five days. Pregnant fem ales from an experimental population, selected for the domestic type o f behavior and, as a control group, females from a commercial populati on, were used. At the end of prenatal development (days 45-50) the con centration of progesterone in adrenals was show to be significantly lo wer in embryos from mothers of the selected population, than in the un selected control group. On the contrary, the domesticated and wild ani mals did not differ in the level of progesterone in blood. The results suggest that selection of animals for domestic behavior decreases the synthesis of progesterone by embryonic adrenal glands.