Effects of domestication on the reproductive biology in the species Canis l
upus were studied by comparing some reproductive biological parameters in m
ale wolves and domestic dogs living under similar conditions.
1. Seasonal changes in the concentrations of the two androgens testosterone
(T) and 5 alpha -dihydrotestosterone (DHT) in the peripheral plasma and in
the relative testicular weights (testes/carcass weight) were observed in t
he wolves with maximal values during the winter, their natural mating seaso
n. In the domestic dogs such seasonal changes were not seen, androgen conce
ntrations and relative testicular weights were high during all seasons.
2. An allometric comparison of testicular and epididymal weights revealed n
o differences among the various breeds of domestic dogs studied here. The w
eights of the testes and epididymides increased almost isometrically with b
ody weight. Compared to the corresponding values in wolves during the matin
g season the weights of the testes and epididymides had increased by about
40% in domestic dogs.
3. Plasma T- and DHT-concentrations in 4 standard poodles, 2 toy poodles, a
nd 3 wolves rose steeply in their 28th, 32nd, and 34th week of life, respec
tively. Thus, poodles and wolves living under similar conditions in captivi
ty reach physiological sexual maturity at nearly the same age.
According to these findings domestication had no or little effect on the on
set of puberty in the species Canis lupus. The seasonality of reproduction
as it was observed in wolves, has vanished in the domestic dog and is repla
ced by the capability to reproduce during any season. The testes, sites of
sperm production, and the epididymides, sites of sperm storage, have been e
nlarged by about 40% during domestication.