Biosynthesis of testosterone in the gonads in silver fox embryos after long-term selection for domesticated behavior

Fetal gonad weight and testosterone content in serum and gonads were analyzed in silver fox every five days from the 35th day of pregnancy until delivery. Fetal testicles were also tested for testosterone production induced by chorionic gonadotropin (CG) in vitro. Pregnant females were sampled from an experimental population subjected to selection for domesticated behavior and a commercial population (control). Fetal gonad weight was significantly lower in domesticated animals than in controls. No differences were revealed in the testosterone contents in their serum and gonads and in the basal production of testosterone in fetal testicles. CG-induced production of testosterone was detectable from the 40th day of fetal development in domesticated animals and from the 50th day in controls. The results obtained suggest that domestication results in the hetero-chronic fetal development of the hypophysial-testicular complex in silver fox.