Ga. Lincoln et Njc. Tyler, Role of oestradiol in the regulation of the seasonal antler cycle in female reindeer, Rangifer tarandus, J REPR FERT, 115(1), 1999, pp. 167-174
Reindeer (or caribou), Rangifer tarandus, is the only extant species of dee
r in which females as well as males normally develop antlers that are cast
and regrown each year. This study investigated the role of ovarian oestradi
ol in the regulation of the seasonal antler cycle in female reindeer. Ovari
ectomized Norwegian reindeer living outdoors in northern Norway (69 degrees
N) were treated with continuous-release subcutaneous Silastic implants con
taining oestradiol, which maintained the blood concentrations of oestradiol
within the physiological range for the mating season from June to October-
November. The treatment with oestradiol induced the synchronized maturation
of the antlers and rapid cleaning of the velvet-like skin in August-Septem
ber in the ovariectomized reindeer, a pattern very similar to that observed
in ovary-intact controls living under the same conditions. The removal of
the steroid implant in October-November caused the premature casting of the
antlers in early winter in two of five animals, while the remainder cast a
t the normal time in spring; this response was seen whether the animals had
received one or two oestradiol implants in autumn. The antlers developed b
y the ovariectomized, oestradiol-treated females were significantly heavier
and carried more branches than the ovariectomized animals without oestradi
ol replacement, and were marginally heavier than the antlers of intact cont
rols. These results support the view that oestradiol is the biologically ac
tive steroid secreted by the ovary in intact female reindeers that induces
the normal development of the antlers. Oestradiol stimulates the growth and
mineralization of the antler bone, the cleaning of the velvet, and suppres
ses the casting of the hard antlers. This endocrine control ensures that th
e hard antlers, which function as weapons, are retained throughout the autu
mn and winter when the females are normally pregnant and when competition b
etween females over food in the snow is most intense; hence there is a repr
oductive advantage to explain the evolution of antlers in females.