ISSN 1022-7954, Russian Journal of Genetics, 2006, Vol. 42, No. 5, pp. 532–538. © Pleiades Publishing, Inc., 2006.
Original Russian Text © I.I. Korshikov, E.A. Mudrik, 2006, published in Genetika, 2006, Vol. 42, No. 5, pp. 659–666.
Studying of the systemic organization of popula-
tions within species, including its signiﬁcant compo-
nent, genetic variability, at different stages of individual
development, is an important issue in resolving the
problem of conservation of intraspeciﬁc diversity.
Analysis of age dynamics of the genetic population
structure may be of key signiﬁcance for understanding
mechanisms that underlie maintenance of genetic
diversity during the individual development and the
evolution of populations . Literature evidence on
realization of hereditary biochemical diversity in gen-
erations of conifers indicates that populations of many
species at the early ontogenetic stages (seed embryos)
are characterized by an excess of homozygotes, exhib-
iting a signiﬁcant shift of the observed genotype distri-
bution from Hardy–Weinberg proportions. Intrapopula-
tion groups of coniferous plants at the middle and late
phases of development generally show a small deﬁ-
ciency or an excess of homozygotes and an equilibrium
distribution of genotypes [2–8]. The genetic diversity is
regulated by selection, which preferentially acts on
resistant individuals, altering their proportion in differ-
ent age groups of a population [1, 9–12].
Of particular importance are studies of the age
dynamics of the gene pools in rare endemic and vanish-
ing species, which can shed light on adverse shifts in
their gene diversity. In small isolated populations of
such species, the normal inbreeding–outbreeding bal-
ance may be disturbed, owing to changes in their demo-
graphic structure and an increase of self-pollination,
especially in years characterized by adverse weather
conditions [13–15]. Impact of extreme natural climatic
factors and a reduction in the proportion of outcrossing
under suboptimal growing conditions may affect the
adaptive optimum of heterozygosity by means of
changing the proportion of homozygous and heterozy-
gous genotypes in its population systems .
The aim of the present work was to examine the age
dynamics of genetic variability in a small isolated pop-
ulation of chalk pine
Kalenicz. ex Kom. at the southern border of its natural
range in order to understand the balance of integration
and differentiation of the gene pool of this species.
MATERIALS AND METHODS
The sole Ukrainian locality of natural growth of the
relict chalk pine, conﬁned to the chalk deposits on the
right bank of the Severskii Donets River , is situ-
ated on the territory of the Svyatye Gory National Park.
The park is located in northern Donetsk oblast in the
steppe zone of Ukraine. The total area of the chalk pine
is 60.5 ha with low tree density. We collected seeds in the
central part of the park, from trees of three age catego-
ries: more than 100 years of age (24 plants), 40–80 years
of age (29 plants), and 25–35 years of age (19 plants).
To determine the genotype of the maternal plant and
seed embryos, we used isozymes of six enzyme systems:
glutamate oxaloacetate transaminase (GOT, E.C. 184.108.40.206),
glutamate dehydrogenase (GDH, E.C. 220.127.116.11), acid
phosphatase (ACP, E.C. 18.104.22.168), leucine aminopepti-
Age Dynamics of Genetic Variation in an Isolated Population
of Chalk Pine
Kalenicz. ex Kom.
I. I. Korshikov and E. A. Mudrik
Donetsk Botanical Garden, National Academy of Sciences of Ukraine, Donetsk, 83059 Ukraine;
fax: (0622) 94-11-90; e-mail: firstname.lastname@example.org
Received June 9, 2005; in ﬁnal form, December 12, 2005
—Based on analysis of variation at ten allozyme loci in three age groups (25–35, 40–80, and more
than 100 years of age) of plants and in seed embryos, demographic dynamics of the gene pools was studied in
a small (60.5 ha) isolated relict population of chalk pine
Kalenicz. ex Kom. from
the steppe zone of Ukraine. The observed grenotype proportions in these tree groups were shown to ﬁt Hardy–
Weinberg expectations, while in the embryos of their seeds, an excess of homozygotes was observed at ﬁve to
nine loci. The mean observed heterozygosity in the sample of old (>100 years of age) trees (
= 0.225) was
substantially lower than in trees of the two other age groups (
= 0.307; 0.311), but signiﬁcantly higher than
in the corresponding embryo samples (
= 0.183–0.207). No allele and genotype heterogeneity of the mater-
nal trees and embryos of their seeds was found. However, heterogeneity was high when the progeny of trees of
different ages, particularly in pairs with old trees, were compared.