STEROID-HORMONES AND REPRODUCTIVE-BEHAVIOR IN SILVER FOX MALES

The silver fox (Vulpes vulpes), a colour mutant of the red fox is an e conomically valuable fur animal in northern countries It has been bred in captivity from the beginning of the 20th century. Reproductive phy siology of the silver fox has been studied only scantily. There is sti ll a need to obtain information about the relations between hormones a nd reproductive behaviour in this species. The main aim of this report is to investigate the role played by socio-sexual contacts between ma les and females in the regulation of testosterone, estradiol and corti sol blood levels in silver fox males when exposed to females during di fferent periods of the reproductive cycle. In captive foxes the breedi ng season extends from January to March. Silver fox males were tested for sexual and agonistic behaviour related to sexual interactions duri ng different stages of the reproductive cycle in September, January an d February. High levels of aggressive interactions between sexes and v ery small number of mountings were observed in September and in Januar y when the female introduced to the male was in anoestrus. In February , the introduction of a receptive female to the male resulted in decre ased aggressive behaviour and increased sexual behaviour in pairs We o bserved wide variations in plasma levels of testosterone and estradiol , but not in those of cortisol between different stages of the reprodu ctive cycle. During the reproductive season, silver fox males responde d to the introduction of a female with a significant increase in their plasma testosterone and estradiol levels when a female was in anoestr us. In contrast, levels of these hormones did not change in males when they encountered a receptive female. A female did not elicit any cort isol response in males during all the periods of the reproductive circ le studied.