1067-4136/02/3302- $27.00 © 2002
Russian Journal of Ecology, Vol. 33, No. 2, 2002, pp. 125–128. Translated from Ekologiya, No. 2, 2002, pp. 137–141.
Original Russian Text Copyright © 2002 by Ivanova.
The topic of biological diversity is becoming an
urgent problem in biology, as industrial activities cause
drastic changes in natural ecosystems. In this context,
of special interest are studies on new species appearing
in the regional faunas. In the case of amphibians, some
species are introduced or reintroduced on purpose,
whereas others appear in the natural environment acci-
dentally, e.g., are released into a water body together
with ﬁsh or escape from scientiﬁc laboratories (Topork-
, 1979; Vershinin, 1990; Breuckmann and
Kupfer, 1998). The introduced species may have not
only favorable, but also adverse effects on the natural
fauna by competing with aboriginal species, extermi-
nating prey, contaminating the gene pool, and bringing
in new pathogens and parasites (Moyle, 1973; Haffner,
1997). Studies on the pathways of their adaptation to
new conditions are of considerable interest, because
this factor determines whether an introduced species
would contribute to biodiversity or would disappear. In
the Middle Urals, one such species is the marsh frog
Pall. The analysis of both the biology
of this species and the features of its population struc-
ture is especially interesting in view of S.S. Shvarts’
(1960) note that populations are capable of adaptively
responding to changes in the environment.
MATERIAL AND METHODS
Marsh frogs (
Pall.) were studied in
cooling ponds of two thermal power plants into which
this species was introduced accidentally. These water
bodies are located 100 km away from one another and
differ in their conditions (Ivanova, 1995). Studies were
performed in spring and summer, from 1995 to 2000.
Adult frogs were measured and weighed, their age was
determined, and the dates of spawning were recorded.
In larvae, the rates of growth and development were
studied. Fecundity was estimated by calculating eggs in
the ovaries of females caught at spawning sites. To pre-
pare total mounts, the gonads were ﬁxed in Bouin’s
ﬂuid. The state of the gonads was analyzed in histolog-
ical sections prepared by conventional methods and
stained with Heidenhain’s iron hematoxylin (Roskin
and Levinson, 1957). The stages of egg development
were determined using the maturity scale proposed by
(1979). The absolute age was deter-
mined by analyzing the sections of phalanxes (Kleinen-
berg and Smirina, 1969).
RESULTS AND DISCUSSION
The spawning period in the marsh frog was shown
to last for more than three months (Bannikov, 1957;
, 1979; Kyriakopoulou-Sklavounou
and Loumbourdis, 1990). According to observations
made in this study, the ﬁrst and last clutches appear in
the Verkhne-Tagil Reservoir in late April and early July,
respectively; thus, the duration of spawning is about
three months. The larval period is 50–70 days. In July,
postmetamorphic juveniles start emerging from water.
This continues until frosts. As the spawning period is
prolonged, some tadpoles developing from the eggs
laid in the end of the spawning season fail to complete
their development and have to overwinter. They emerge
from water in late May to early June in the next year.
Thus, the same age class is represented by “asynchro-
nous” cohorts, and it is noteworthy that the animals
from eggs laid in different periods have virtually the
same body size when they complete their larval devel-
opment (Ivanova, 1991). The average body length in
metamorphic animals varies insigniﬁcantly from year
Marsh Frog (
in Cooling Ponds in the Middle Urals
N. L. Ivanova
Institute of Plant and Animal Ecology, Ural Division, Russian Academy of Sciences,
ul. Vos’mogo Marta 202, Yekaterinburg, 620144 Russia
Received April 28, 2001
—Environmental conditions in cooling ponds of thermal power plants are favorable for marsh frogs.
Their populations inhabiting Verkhne-Tagil and Reftinskoe reservoirs differ in some traits, such as size and age
composition, growth rate after metamorphosis, spawning type, fecundity, and characteristics of larval develop-
ment. Differentiation in body size manifests itself at the early stages of terrestrial life and progresses at later stages.
As a consequence, larger individuals may reach maturity and participate in reproduction at an earlier age.
: amphibians, marsh frog, metamorphosis, oocyte, fecundity.