ISSN 10227954, Russian Journal of Genetics, 2015, Vol. 51, No. 12, pp. 1249–1252. © Pleiades Publishing, Inc., 2015.
Original Russian Text © E.A. Mudrik, T.A. Kashentseva, K.A. Postelnykh, G.V. Nosachenko, D.V. Politov, 2015, published in Genetika, 2015, Vol. 51, No. 12, pp. 1439–1443.
The sex ratio in different animal species depends
on different biological and environmental factors. The
primary sex ratio (estimated immediately after fertili
zation) is usually close to 1 : 1; the secondary and adult
sex ratio (estimated after birth and at the beginning of
reproductive age, respectively) can shift toward either
males or females depending on offspring viability, the
parent investment, and environmental conditions.
However, it has been found that the sex ratio of a num
ber of vertebrates shifts already at the fertilization stage
[1, 2]. In birds, females are the heterogametic sex;
therefore, the female can influence the sex of future
offspring by hormonal regulation. The formation of
follicles with the preferred sex chromosome is stimu
lated, and follicles with the undesired sex chromosome
are aborted [3, 4]. Such regulation usually involves the
first egg in a clutch and usually does not involve the
second [1, 5]. In some species of birds, a male bias is
observed in earlier clutches; a female bias is seen in
later clutches .
Processes causing biases the in secondary sex ratio
can result from age, longevity, relatedness, and mono
or polygamy of parents, as well as from the energy cost
required for feeding the chicks of a certain species.
Female chicks are usually more viable and less sensi
tive to growth conditions and require a lower energy
cost for feeding than male chicks [6–8]. According to
some observations, a female bias in the offspring is
more frequent for young and old parents and birds
with irregular reproduction; a male bias in the off
spring is more typical for middleaged parents with
high reproductive success . However, this tendency
is not observed in some species with reversed sexual
dimorphism (for example, birds of prey); a male bias is
typical for the offspring of these species, since the
males are smaller than the females and require a lower
energy cost for feeding . In polygamous species,
when the probability of consanguineous mating is
high, a female bias in offspring is frequent as well,
since females are less affected by inbreeding depres
sion; at the same time, male bias is typical for out
crossing . A female bias is also frequent in pairs in
which the male parent is aggressive .
The sex ratio in cranes is poorly studied. There is
some evidence of a female bias in the Redcrowned
Muller) and of a relative parity
of male and female chicks in the offspring of the Sibe
rian crane (
Pallas) and Whitenaped
Pallas) in captive populations .
However, that study was based on data from different
years, including those when the chick’s sex was deter
mined without the use of molecular methods, i.e.,
when the sex of dead embryos was not determined.
Uncontrolled mating and the problem of sample col
lection, especially in rare species such as
, make studies of the crane sex ratio in natural pop
ulations considerably difficult. Studies carried out in
the captive population provide an opportunity to ana
lyze the offspring sex ratio, not only under natural
mating but also in dams fertilized by artificial insemi
Offspring Sex Ratio in the Captive Population
of the Siberian Crane (
E. A. Mudrik
, T. A. Kashentseva
, K. A. Postelnykh
G. V. Nosachenko
, and D. V. Politov
Vavilov Institute of General Genetics, Russian Academy of Sciences, Moscow, 119991 Russia
Oka Crane Breeding Center, Oka State Nature Biosphere Reserve, Brykin Bor, Ryazan oblast, 391072 Russia
Received June 24, 2015
—The sex ratio of Siberian crane chicks (
Pallas) from the captive population of
the Oka Crane Breeding Center was analyzed with the use of molecular sex marker EE0.6 in 2009–2014. We
determined the sex of 84 birds bred from 12 dams by means of artificial insemination and natural breeding.
The total primary sex ratio was 40 : 44, and the secondary sex ratio was 36 : 39 with a minor female bias. The
mortality rate of embryos was the same for both sexes. The primary and secondary sex ratio for the first eggs
in clutches were inline with total sex ratio. The relatedness of parents by microsatellite loci has no effect on
sex ratio in chicks of naturally and artificially propagating dams.
: Siberian crane, sex determination, unique sequence EE0.6, male, female, captive breeding