1062-3604/03/3401- $25.00 © 2003
Russian Journal of Developmental Biology, Vol. 34, No. 1, 2003, pp. 36–41. Translated from Ontogenez, Vol. 34, No. 1, 2003, pp. 43–49.
Original Russian Text Copyright © 2003 by Sheiman, Sakharova, Tiras, Shkutin, Isaeva.
Some planarians (Turbellaria, Triclada) are repro-
duced by the asexual way: cross architomic ﬁssion.
Regeneration of planarians is also based on the mor-
phogenetic process, to which asexual reproduction is
related. However, the asexual reproduction of planari-
ans is characterized by certain patterns, which are
determined by both external and internal factors. It is
regulated by the density of planarians in a vessel (Best
, 1974; Sakharova
, 1975; Sheiman, 1984):
they ﬁssion most intensively when placed one in each
vessel. The ﬁssion of the planarians
was shown to depend on the cephalic ganglion,
which inhibits ﬁssioning (Best
, 1975). Neurose-
cretion was also shown to be essential for asexual
reproduction (Lender and Zhgal, 1969). The processes
occurring in the transpharyngeal zone, or zone of ﬁs-
sioning, were studied (Isaeva, 1972; Krichinskaya,
1973). Tokin (1987) explained this ﬁssioning through
local disintegration of tissues.
The role of physical factors in asexual reproduction
of planarians has been insufﬁciently studied. It was
reported that temperature affected ﬁssioning (Vow-
inckel and Marsden, 1971), planarians preferred night
time for ﬁssioning (Morita and Best, 1984), and weak
electromagnetic ﬁelds affect ﬁssioning (Sheiman and
Fesenko, 1999). There were no observations of ﬁssion-
ing of planarians during the day time and this made to
us to study in detail the ﬁssioning of planarians as a
function of diurnal cycle, light regime, and time zone.
MATERIALS AND METHODS
Studies were carried out on the asexual race of pla-
Keeping of planarians.
Planarians were kept in glass
10-l vessels with a mixture of tap and distilled water
(2 : 1) at the temperature ca. 20
C in semidarkness.
They were fed on midge larvae once a week.
For experiments, planarians were
taken on the 3rd–4th after feeding. Fifty planarians, 12–
13 mm long, with a sharp tail end (evidence of restora-
tion after the last ﬁssioning) were placed in glasses with
50 ml water, one in each. The planarians were selected
and placed in glasses at 4 pm. Subsequently, ﬁssioned
planarians were samples every 8 h, i.e., at 12 pm, 8 am,
and 4 pm. The experiments were repeated ﬁve to six
times. Artiﬁcial illumination was used for light manip-
All experiments consisted of two parts: the popula-
tion of planarians was ﬁrst kept under certain condi-
tions for a week and then transferred in the set condi-
In order to study the role of time zone in behavior,
planarians were ﬂown in plastic bottles placed in a dark
bag by air from the Moscow District to the Far East
(Vladivostok and Komsomol’sk-na-Amure). The mean
experimental data were expressed as the number of ﬁs-
sioned planarians from the number of nonﬁssioned dur-
ing each day of experiment in %.
Regulation of Asexual Reproduction
of the Planarians
I. M. Sheiman*, N. Yu. Sakharova**, Kh. P. Tiras**, M. F. Shkutin*, and V. V. Isaeva***
* Institute of Cell Biophysics, Russian Academy of Sciences, Pushchino, Moscow oblast, 142290 Russia
** Institute of Theoretical and Experimental Biophysics, Russian Academy
of Sciences, Pushchino, Moscow oblast, 142290 Russia
*** Institute of Marine Biology, Far Easter Branch of the Russian Academy of Sciences,
ul. Pal’chevskogo 17, Vladivostok, 690041 Russia
Received December 7, 2001; in ﬁnal form, January 23, 2002
—We studied asexual reproduction of planarians under the natural and artiﬁcial photoperiodic condi-
tions. It was shown that light inhibits the ﬁssion of planarians, while darkness stimulates it. The diurnal dynam-
ics of the ﬁssion of planarians demonstrated a circadian rhythm. This rhythm is stable, which is expressed when
the conditions are experimentally changed: constant darkness, unnatural rhythm of light-darkness succession).
However, this stability is affected at the time zone change. The planarians are adapted to new conditions and
begin to ﬁssion at once in correspondence with the new diurnal regime.
: planarians, asexual reproduction, circadian rhythm, time zone.