ORIGINAL ARTICLE
Photoperiodism, pineal clock and seasonal reproductionin the Indian Weaver Bird (Ploceus philippinus)
Sangeeta Rani Æ Sudhi Singh Æ Vinod Kumar
Received: 24 April 2007 / Revised: 24 September 2007 / Accepted: 25 September 2007 / Published online: 24 October 2007
� Dt. Ornithologen-Gesellschaft e.V. 2007
Abstract Previous studies show that, in birds, pineal
melatonin is important for circadian rhythmicity, and cir-
cadian rhythms mediate photoperiodic effects. The effect
of pinealectomy or melatonin administration in photo-
periodic induction of testicular growth is not found in many
bird species. This is inconsistent with the fact that avian
pineal is a self-sustained circadian biological clock and
decodes both the daily and annual photoperiodic informa-
tion. Does this mean that the pineal clock in birds regulates
circadian rhythms, but not the one that is involved in the
photoperiodic induction of the seasonal response? We have
examined this in experiments on the subtropical Indian
Weaver Bird (Ploceus philippinus). We investigated the
effects of the absence of the pineal gland or exogenous
melatonin administration on circadian rhythmicity in
activity, and on photoperiodic induction of testicular
growth, androgen-dependent beak pigmentation and
luteinizing hormone-specific plumage coloration. Weaver
birds were subjected for several weeks to short day length
(8 h light: 16 h darkness, 8L:16D), long day length
(16L:8D) and to light–dark cycles that tested the involve-
ment of circadian rhythmicity in photoperiodic time
measurement. The results show that circadian pineal clock
may regulate the circadian rhythm in activity, but is not
essential for the expression of photoperiodism associated
with the photoperiodic induction of testicular growth. This
suggests that the circadian activity and photosensitivity
rhythms are outputs of different circadian oscillators or of
the same set of circadian oscillators, but that they are not
closely coupled.
Keywords Circadian rhythm � Melatonin � Photoperiod �Pineal � Ploceus philippinus
Introduction
Day length regulates seasonal cycle of gonadal growth and
regression in many birds (Gwinner and Hau 2000; Dawson
et al. 2001). An endogenous clock system sensitive to light
enables the bird to synchronize its physiological activities
at the appropriate time of the day and time of the year
(Kumar and Follett 1993a; Kumar et al. 1996a). In a typical
photoperiodic species that uses long days to initiate its
gonadal growth and development, endogenous circadian
rhythm sensitive to light becomes photoinducible about
12 h after dawn each day. Hence, spring and summer day
lengths with light period ‡12 h per day are read as a ‘‘long
day’’ and result in induction of gonadal growth and
development. Conversely, autumn and winter day lengths
with light period \12 h per day are read as ‘‘short day’’
and, consequently, there is no photoperiodic induction of
gonadal growth (Kumar and Follett 1993a).
The clock system in birds appears to have multiple
independent pacemakers sited in a minimum of three pla-
ces—the hypothalamus (avian SCN), the pineal gland, and
the retina of eyes (Kumar et al. 2004; Kumar and Singh
2006). Unlike in mammals, where the input, pacemaker
and output are localized in different structures, all the three
avian clocks have independent input–pacemaker–output
systems. Hence, the avian pineal is an autonomous clock
with its own input–oscillator–output systems (summary in
Communicated by F. Bairlein.
S. Rani (&) � S. Singh � V. Kumar
DST-IRHPA Unit on Biological Rhythm Research,
Department of Zoology, University of Lucknow,
Lucknow 226 007, India
e-mail: [email protected]
123
J Ornithol (2007) 148 (Suppl 2):S601–S610
DOI 10.1007/s10336-007-0236-z
Gwinner et al. 1997; Kumar et al. 2004; Kumar and Singh
2006). The melatonin produced at night is the best known
output of the pineal gland. The secretion of melatonin
tracks the night length (= day length; Kumar and Follett
1993b). It is also shown that the avian pineal decodes daily
and annual photoperiodic information both in the duration
and amplitude of its melatonin output (Kumar and Follett
1993b; Brandstatter et al. 2000a, b; Kumar 2001). There-
fore, melatonin could play a key role in photoperiodic
control of the daily and seasonal rhythms in vertebrates. In
fact, both winter and summer breeding mammals use
melatonin in photoperiodic regulation of their reproductive
cycle (for references, see review in Lincoln et al. 2003).
In birds, however, the effect of pinealectomy or mela-
tonin administration in photoperiodic induction of testic-
ular growth is not significant, although a few studies do
show the effects of pinealectomy and exogenous mela-
tonin on gonadal growth and regression (see review in
Kumar 2001). It will be interesting to consider whether
the absence of the effects of pinealectomy or exogenous
melatonin on photoperiodic induction of gonadal devel-
opment would mean the absence of the role of pineal
melatonin in regulation of reproduction in birds. This
might not be the case since, in a recent study, Ubuka
et al. (2005) have clearly shown the effects of pinealec-
tomy on the expression of gonadotropin-inhibitory
hormone (GnIH) in the Japanese Quail (Coturnix coturnix
japonica). GnIH is a recently identified neuropeptide
whose expression is photoperiodically controlled. The
expression of GnIH is high under short days when the
duration of nocturnal melatonin is increased, and low
under long days when the duration of nocturnal melatonin
is decreased (Ubuka et al. 2005). Ubuka et al. (2005)
further found that pinealectomy combined with orbital
enucleation (in Japanese Quail, the eyes produce a sig-
nificant amount of melatonin, Underwood et al. 1984)
decreased the expression of GnIH precursor mRNA and
content of peptide in the brain, and melatonin adminis-
tered to pinealectomized and enucleated quails restored
both of them in a dose-dependent manner.
Regardless of its effect on photoperiodism, the pineal
clock is important for avian circadian rhythmicity. Nearly
four decades ago, Gaston and Menaker (1968) reported
arrhythmicity in locomotor activity pattern of pinealec-
tomized House Sparrow (Passer domesticus). In a later
study, the same group reported that after a pineal from
another sparrow was transplanted into the anterior chamber
of the eye, pinealectomized arrhythmic sparrows become
re-rhythmic with the phase of the donor (Zimmerman and
Menaker 1979). Disruption of circadian rhythmicity was
further confirmed in several other bird species when either
the pineal was removed or birds were implanted with
melatonin-filled silastic tubes which elevated the blood
melatonin levels such that the rhythmicity in melatonin
itself was abolished (Gwinner et al. 1997; Kumar 2001).
Therefore, it is important to consider whether in birds
the photoperiodic induction and activity-rest cycles, both
mediated by the circadian system, are outputs of the same
circadian oscillator or of the same set of circadian osci-
llators that are very closely coupled or of different
circadian oscillators. The present mini-review article will
focus on this, with the background of a brief summary of
the results on role of pineal in activity rhythms and pho-
toperiodic induction of primary and secondary sexual
characteristics in the Indian Weaver Bird (Ploceus philip-
pinus), a photoperiodic subtropical passerine finch (also
known as the Baya Weaver). Interestingly, a few previous
studies have recorded activity rhythms in support of the
evidence that circadian system is involved in the photo-
periodic time measurement (see, e.g., Hamner and Enright
1967; Elliott et al. 1972). This was done with the
assumption that circadian activity rhythm reflects the
characteristics of the circadian rhythm that underlies
photoperiodism.
Photoperiodism and circadian rhythms in the Indian
Weaver Bird
The Indian Weaver Bird (Ploceus philippinus) is a sea-
sonally breeding species with the breeding season
extending between May and September (Ali and Ripley
1974) (Fig. 1). The onset of gonadal growth is triggered by
increasing late spring/summer day lengths, and the breed-
ing season ends in early fall with the development of
photorefractoriness which is evidenced by the onset of
gonadal regression and molt (Saxena 1964; Nair and
Chandola-Saklani 1998; S. Rani et al., unpublished).
Annual gonadal cycle of the Indian Weaver Bird is
described in four phases: preparatory, progressive, breed-
ing, and regressive (Saxena 1964). Laboratory
investigations have also confirmed the role of environ-
mental photoperiod in regulation of the Weaver Bird’s
reproductive cycle. Day lengths ‡12 h per day initiate
testicular recrudescence, and post-stimulation Weaver
Birds become refractory, albeit briefly, to stimulatory
photoperiods equivalent to what they experience in the
wild (Thapliyal and Tewary 1964; Singh nee Pavgi and
Chandola 1981; Chakravorty and Chandola-Saklani 1985;
Nair and Chandola-Saklani 1998). Using standard lighting
protocols (see Kumar and Follett 1993a), it has been
demonstrated that the circadian rhythm sensitive to light
appears mediating photoperiodic induction of gonadal
recrudescence in Weaver Birds (Chandola et al. 1976;
Pavgi and Chandola 1983).
S602 J Ornithol (2007) 148 (Suppl 2):S601–S610
123
The Indian Weaver Bird is diurnal species being active
during the day. The circadian control of activity and its
synchronization has been readily documented in the fol-
lowing experiment. Birds were released into constant dim
light condition (LLdim) following exposure to a pro-
grammed light–dark (LD) cycle in order to examine the
phase and period of the circadian rhythm as assayed by a
behavioral (activity) rhythm. The details of the experiment
are as follows. Birds (n = 5) were subjected to a complete
photoperiod [12 h light (400 lux):12 h darkness
(= \1 lux); 12L:12D] for 24 days and then released into
constant dim light conditions (LLdim, \1 lux; nighttime
illumination). On day 13 of LLdim, a single 4-h light period
(400 lux) was introduced in the subjective night beginning
at zeitgeber time 12 (ZT 12; ZT 0 = light onset of previous
12L:12D) to examine the response of circadian system to a
light perturbation. Birds remained in LLdim for another 7
days and then returned to 12L:12D. After 17 days of
resynchronization to 12L:12D, the lighting protocol was
changed to the corresponding skeleton photoperiod
(1L:10D:1L:12D) by introducing a 10-h dark period
(\1 lux) beginning at ZT 2. After 9 days of skeleton
photoperiod, birds were again released into LLdim.
Activity-rest pattern was continuously measured as the
bird’s general activity within its cage, as described else-
where (Malik et al. 2004; Trivedi et al. 2006). Briefly, each
bird was housed in a specially designed activity cage fur-
nished with two perches and mounted with a Passive
Infrared Motion Sensor [C & K Systems (Intellisense
XJ-413T) Conrad Electronic, Germany, Haustier PIR-
Melder]. Each sensor detected the movement of the bird
within the cage, and this information was stored on the
computer and analyzed using a software program from
Stanford Software Systems, Stanford, USA.
Figure 2 presents the data. There was a clear bimodal
activity pattern under 12L:12D: the activity in the morning
(*3 h) and evening (*1 h) was significantly higher
(P \ 0.05; one-way RM ANOVA, Student Newman Keuls
post hoc test;) than in the rest of the light period (Fig. 2a).
Such activity pattern seen in several other species is con-
sistent with a two-oscillator, the morning (M) and evening
(E), circadian system governing and synchronizing circa-
dian rhythms of Weaver Birds with the environmental
photoperiod (Aschoff 1981; Pittendrigh 1981; Daan et al.
2001). That the activity-rest cycles of the Indian Weaver
Birds were indeed circadian was confirmed from the data
under LLdim, in which all the individuals exhibited activity
pattern with the mean (±SE) period of 23.7 ± 0.34 h, and
the phase of activity was maintained after environmental
synchronization. Secondly, their sensitivity to light as an
environmental zeitgeber was demonstrated by the delayed
phase shift in response to a single 4-h light pulse at ZT12 as
a result of single light perturbation. Here, the mean (±SE)
circadian period of activity rhythm was changed to
24.78 ± 0.47 h (Fig. 2b).
Return to 12L:12D re-established the bimodality in
activity pattern. The amplitude of activity at this time
appeared slightly lower, perhaps due to acclimation to the
caged situation, but the difference between two 12L con-
ditions was not significant (P [ 0.05; two-way ANOVA)
(Fig. 2a,c). The change to skeleton paradigm restricted
activity mainly to short light periods, perhaps due to
masking effects (Fig. 2d). In the following LLdim, two of
five birds appeared to have lost their circadian rhythm
(s[ 27 h), but three individuals still retained circadian
rhythmicity with the mean (±SE) period of 24.25 ± 0.41 h
(Fig. 2e). Whether the loss of circadian rhythmicity in
some individuals was due to exposure to the skeleton
photoperiod, needs to be investigated.
Photoperiodic induction in the Indian Weaver Bird:
role of pineal and melatonin
More than three decades ago, Balasubramanian and Saxena
(1973) reported the acceleration of testis growth, the
darkening of androgen-dependent beak color and the
yellow pigmentation of luteinizing hormone (LH)-depen-
dent plumage in pinealectomized birds held under naturally
increasing day lengths or exposed to artificial long day
lengths (18L:6D). More interestingly, when reproductively
mature Weaver Birds were pinealectomized and exposed to
short day lengths (9L:15D), a non-stimulatory photoperiod
which causes full testicular regression and concomitant
changes in secondary sexual characters, there was only a
Fig. 1 A schematic plot of the seasonal reproductive cycle of the
Indian Weaver Bird (Ploceus philippinus) based on information as
reported in the literature (Ali and Ripley 1974; Saxena 1964;
Thapliyal and Saxena 1964). Alphabets at the periphery indicate
months of the year. Note the temporal relationship between changes
in day lengths of late spring/summer and different reproductive
activities
J Ornithol (2007) 148 (Suppl 2):S601–S610 S603
123
transient and partial regression of testes; pinealectomized
individuals never fully regressed, lightened their beak to
straw color or de-pigmented their plumage to the non-
breeding (‘‘female like’’ or ‘‘henny’’) type. The results,
which clearly evidenced an inhibitory role of the pineal
gland on annual reproductive cycle of Indian Weaver
Birds, were significant and generated lots of interest since
they were inconsistent with the majority of results from
experiments done on birds since then. Therefore, in a
recent study reported elsewhere, Rani et al. (2005) have
investigated whether the pineal had indeed an inhibitory
role under short days. In this experiment, Indian Weaver
Birds were pinealectomized during different phases of the
annual cycle and exposed to short (8L:16D) and long day
lengths (16L:8D). The changes in testicular size and
pigmentation of beak and plumage were recorded at regular
intervals.
Pinealectomized and sham-operated Weaver Birds
(n = 6–8 each) were exposed to short day lengths (in late
September) when they had almost regressed testes [mean
(±SE) testis volume (TV) = 3.09 ± 0.45 mm3] but dark
pigmented beak [mean (±SE) score = 3.15 ± 0.13] and
nuptial plumage [mean (±SE) score = 3.00 ± 0.00, head;
5.00 ± 0.00, breast], and to long day lengths (in early
March) when they had small testes [mean (± SE) TV =
0.34 ± 0.07 mm3], unpigmented beak and ‘‘female-like’’
plumage.
The dimensions of the left testis were measured by
unilateral laparotomy under local anesthesia as described
by Kumar et al. (2001), and from this TV was calculated
15
25
30
35
40
45
50
55
60
65
70
75
80
Day
sTime of the day
12L:12D (a)
LLdim (b)
12L:12D (c)
Light pulseZT12-16
1L:10D:1L:12D(d)
LLdim (e)
0 6 12 18 24
0 6 12 18 24
0 6 12 18 24
4 h light pulse
Hours
Hours
Hours
0 4 8 12
0 1 2 3 4 5 6 7
Days
Act
ivit
y co
un
ts/ m
inu
te
Days
a
b
c
d
e
0600 1800 0600 1800 0600 0600 1800 0600 1800 0600
Fig. 2 Left panels: double plotted activity recordings of two repre-
sentative male Indian Weaver Birds sequentially exposed to 12L:12D
(a), LLdim (b), 12L:12D (c), 1L:10D:1L:12D (d) and LLdim (e)
(L = 400 lux; D = \1 lux; LLdim = \1 lux). When in the first LLdim,
a single 4-h light pulse (400 lux) was introduced beginning at
zeitgeber time 12 (ZT12, ZT0 = lights on). Horizontal bar at the topshows clock time of the day: 0600 hours—lights ON of an LD cycle.
Right panels: mean (±SE, n = 5) activity profile of all birds in the
experiment at different times of the experiment, compare with
actograms on the left with corresponding figures (a–e). Note a
bimodal activity pattern under 12L:12D and light-restricted activity
under 1L:10:1L:12D. Also note the circadian period under LLdim after
12L:12D changed from (mean ± SE) 23.7 ± 0.34 h to 24.78 ± 0.47
after imposition of 4-h pulse demonstrating the sensitivity of the
circadian clock to single light perturbation
S604 J Ornithol (2007) 148 (Suppl 2):S601–S610
123
using the formula 4/3 p ab2, where a and b denote half of
the long and short axes, respectively. Beak color in males
changes over seasons from non-breeding straw to breeding
dark black. Similarly, the plumage color over the head and
breast changes from non-breeding ‘‘female-like’’ to
breeding (nuptial) bright yellow. We recorded these
changes using a subjective criterion, and considered them
an indicator of the endogenous levels of androgen (beak
color; Saxena and Thapliyal 1962) and LH (plumage color;
Thapliyal and Saxena 1961) levels. We scored both the
beak and plumage colors for better illustration of the
observations and statistical comparisons, as described by
Trivedi (2004; see also Fig. 3). Briefly, beak color was
scored on a scale of 0–5 as follows: 0 = straw in color (S),
1 = straw with a little tinge of blackness (ratio = SSS:B),
2 = slightly blackish (ratio = SS:B), 3 = straw and black in
approximately 50:50 patches (ratio = S:B), 4 = black with
very little straw patch left (ratio = S:BB), 5 = fully black
(B). Similarly, plumage color was scored on a scale of 1–3
[head: 1 = ‘‘female-like’’ feathers; 2 = mixed ‘‘female-
like’’ and yellow (nuptial) feathers; 3 = complete yellow
feathers] or 0–5 [breast: 0 = all ‘‘female-like’’ (no yellow)
feathers; 5 = all yellow (no female-like) feathers; every 0.5
increment in this scale (e.g., 0.5, 1.0 and so on] meant 10%
increase from ‘‘female-like’’ to nuptial feathers].
Figure 4b,d shows that, contrary to the expectation
based on the previous results of Balasubramanian and
Saxena (1973), there was no photostimulation under short
day lengths; instead, relatively larger testes of September
underwent testicular regression. Similarly, testes under-
went significant growth and regression under long day
lengths. The response of both the pinealectomized and
sham-operated birds to short or long day lengths was
essentially similar, except that under long days pinealec-
tomized birds had a faster rate and greater amplitude of the
photoperiodic induction. Changes in beak pigmentation
and plumage color (data not shown) also corresponded to
the effects found on testes. Birds darkened and lightened
their beak, respectively, as they grew, and regressed their
testes, confirming a previous finding of Thapliyal and
Saxena (1961). Also, there were increased numbers of
bright yellow feathers over the head and breast regions in
birds that were stimulated under long days, reflecting the
activity of the hypothalamo-hypophyseal (h-h) axis. A
study of Kumar et al. (2002) showing that exogenous
melatonin given via silastic implants to Weaver Birds in
late August failed to show an effect either on testes or on
androgen-dependent beak color supports the present
results.
Figure 4 (cf. a–d) also compares some of the results from
the two studies on Indian Weaver Birds: those of Bala-
subramanian and Saxena (1973) with Rani et al. (2005),
briefly described above. Clearly, the results from the study
of Rani et al. (2005) were only partially consistent with
those of Balasubramanian and Saxena (1973), as noted
above. However, we suggest that the effect of pinealectomy
on photoperiodic induction in the Indian Weaver Bird is
dependent on the phase of the birds’ annual gonadal cycle.
Also, a reproductive phase dependent effect of the pineal-
ectomy and of exogenous melatonin has been reported,
respectively, in Indian Jungle Bush Quail (Perdicula
asiatica; Haldar and Ghosh 1990) and Rose-ringed Para-
keet, (Psittacula krameri; Maitra and Dey 1992).
In another long-term experiment, we further addressed
on the issue of the role of pineal in photoperiodism of the
Indian Weaver Bird. We pinealectomized or sham operated
Weaver Birds (n = 5 each) in the first week of July 2004
when testes were still large. These birds were kept in an
outdoor aviary (Lucknow, India: 26.55�N, 80.59�E), and
thus experienced the changes in day length that would
occur in wild. Changes in testicular size and beak and
plumage pigmentation were measured over the next 15
Fig. 3 Pictures of head and
breast region of a male Indian
Weaver Bird showing plumage
and beak pigmentation during
their non-breeding (a, b),
transitory (c, d) and breeding (e,
f) stages. On the right hand sideare shown the scores we have
accorded for our study as
described in the text
J Ornithol (2007) 148 (Suppl 2):S601–S610 S605
123
months. Figure 5 shows the results. Testes regressed in
response to decreasing day lengths at the similar rate in
both the pinealectomized and sham-operated birds. With
the increasing day lengths of the following spring/summer,
testes began to recrudesce, but the reinitiation of testis
growth and regression was advanced by about a month in
the pinealectomised group (Fig. 5d). As with the previous
experiment, the changes in beak and plumage pigmentation
corresponded to the effects found on testes (Fig. 5a–c).
Thus, the removal of the pineal affected only the temporal
phasing of the testicular cycle, as suggested earlier by
Kumar et al. (2002) from their study on migratory Red-
headed Buntings (Emberiza bruniceps).
Circadian system in the Indian Weaver Bird:
role of pineal gland
Pineal is part of the avian circadian clock system (Kumar
et al. 2004). Also, as noted above, a direct effect of the
pinealectomy and/or melatonin administration has been
shown in regulation of several circadian rhythms (Gaston
and Menaker 1968; Gaston 1971; Binkley et al. 1971,
1972; Menaker and Zimmerman 1976; Turek et al. 1976;
Binkley and Mosher 1985; Gwinner et al. 1987, 1997;
Beldhuis et al. 1988; Gwinner 1989; Oshima et al. 1989;
Chabot and Menaker 1992; Lu and Cassone 1993a, b; Pohl
2000). Of all the overt markers of the circadian system, the
rhythm of locomotor activity is conveniently measurable
and is also reliable. Therefore, in an experiment, we
examined the role of pineal in regulation of circadian
activity rhythms of Indian Weaver Birds. A group of birds
procured during the preparatory phase of their annual cycle
(first week of January) were subjected to 12L:12D
(L = 50 ± 2 lux; D = \1.0 lux). After 2 weeks, they were
pinealectomized or sham-operated and retained in 12L:12D
for another 2 weeks. Then, they were released into LLdim
(\1.0 lux) for another 2 weeks. Their activity was recorded
continuously as described above.
Figure 6 shows the activity record of the representative
pinealectomized and sham-operated birds. Both birds
showed good entrainment to LD cycle, but thereafter under
LLdim the rhythmicity was lost after a few cycles in the
pinealectomized but not in the sham-operated birds. This
clearly provides evidence for the major role of the pineal
clock in the generation of circadian rhythmicity at least in
behavioral functions. This is consistent with the findings on
other songbirds in which a similar role of pineal is sug-
gested (summary in Kumar 2001). The pinealectomized
birds, however, did not become arrhythmic immediately.
Test
is V
olu
me
(mm
3 )Te
stis
Vo
lum
e (m
m3 )
Test
is V
olu
me
(mm
3 )Te
stis
Vo
lum
e (m
m3 )
Fig. 4 Comparison of the
results from two studies done on
Indian Weaver Birds
investigating the role of pineal
in photoperiodic induction. aand c (adapted from
Balasubramanian and Saxena
1973); b and d (adapted from
Rani et al. 2005). Note the
difference in photoperiod used
in the two studies, but clearly
the results of Rani et al. (2005)
did not support an inhibitory
role of the pineal under short
days
S606 J Ornithol (2007) 148 (Suppl 2):S601–S610
123
Rather, the loss of circadian rhythmicity was gradual. This
indicated that other clocks (i.e., hypothalamic clock)
maintained rhythmicity for a few days in pinealectomized
birds, but the lack of the sustainment of circadian
rhythmicity for a longer period in these individuals clearly
suggested that the input from the pineal to the circadian
system was vital. In birds, the contribution from all the
components of the central clock system appears crucial for
the sustainment of circadian rhythmicity (Kumar et al.
2004). In a previous study, it was shown that the lesions of
the hypothalamic pacemaker resulted in severe impairment
of the rhythmicity in pineal intact House Sparrows
(Takahashi and Menaker 1982). Similarly, complete
removal of eyes (blinding) produced arrhythmicity in the
Japanese Quail (Underwood 1994). In all probability,
therefore, the pineal interacts with the hypothalamic oscil-
lator and possibly the retinal oscillator (Kumar et al. 2004).
Because the pineal is part of the avian timekeeping
system that regulates a variety of circadian rhythms
(Kumar 2001; Gwinner and Brandstatter 2001; Kumar
et al. 2004), its absence should disrupt the circadian
rhythms that helps distinguish Weaver Birds between short
and long days. However, the findings described above
suggest that in Weaver Birds pinealectomy disrupted cir-
cadian activity rhythm but not the photoperiodic time
measurement; pinealectomized birds continued showing
photoperiodic responses characteristic of short and long
days (cf. Figs. 4, 6). Studies on several other species
including European Starling (Sturnus vulgaris; Gwinner
and Dittami 1980), Spotted Munia (Lonchura punctulata;
Chandola-Saklani et al. 1988), Tree Sparrow (Spizella
arborea; Wilson 1991), Japanese Quail (Kumar et al.
1993), Black-headed Bunting (Emberiza melanocephala;
Kumar 1996; Kumar et al. 1996b) and Red-headed Bunting
(Kumar et al. 2002) also showed similar results.
Conclusion and perspective
The pineal clock regulates circadian rhythms, but appears
not to mediate the circadian rhythm-dependent photo-
periodic measurement in the Indian Weaver Bird. It is likely
that the circadian clock regulating photoperiodic induction
is different from the one that regulates other circadian
rhythms, e.g., rhythms in activity–rest. An earlier finding on
Japanese Quail also showed dissociation between circadian
rhythms of photoperiodically induced LH release and
locomotor activity rhythm (Kumar et al. 1993; Juss et al.
1995). A molecular assay of the hypothalamic clock
(median suprachiasmatic nucleus; mSCN) of Japanese
Quail also did not support the role of melatonin in avian
clock system. Given as a single injection or as implants
melatonin did not affect the expression of qper2, qper3 and
qclock, despite the fact that the Quail mSCN had detectable
levels and daily rhythmicity of both Mel 1a and Mel 1c
receptors (Yasuo et al. 2002). The rhythmicity of per2 in the
mSCN of House Sparrows is also not influenced by
0 3 7 11 15 19 23 27 35 39 443 47 51 55 59
0
15
30
45d)
50'tcO40'luJWeeks
Tes
tis v
olum
e (m
m3 )
0
1
2
3
4
5a)
xnip
mahsB
eak
colo
r sco
re
0
1
2
3b)
Hea
d co
lor s
core
0
1
2
3
4
5c)
Bre
ast p
lum
age
colo
r
Fig. 5 Changes in beak and plumage (head and breast) pigmentation
and testicular growth in pinealectomized and sham-operated Indian
Weaver Birds kept under natural photoperiodic variations at Lucknow
(26.55N, 80.59E) for 15 months beginning from July 2004. Note the
advancement in testicular cycle and associated secondary sexual
characters in the pinealectomized birds
J Ornithol (2007) 148 (Suppl 2):S601–S610 S607
123
pinealectomy (Abraham et al. 2003). Interestingly, lesions
of the mSCN abolish circadian rhythms in locomotor
activity. It could be that melatonin acts at the translational
and not at the transcriptional level, and its role is more that
of amplifying the level of oscillations within the central
clock system rather than generating these oscillations. Thus,
as an output from the retina and/or the pineal gland, mela-
tonin exerts control over circadian functions, and absence of
the circadian melatonin output would lead to arrhythmicity.
It may also be probable that the pineal/melatonin might
have input to the site(s) other than the mSCN.
Although a direct effect of pineal and melatonin has not
been found in the majority of bird species investigated so
far, there may still be an indirect effect of them on the
seasonal cycles. For example, pineal melatonin may have
modulatory effects on synchronizing different phases of the
annual reproductive cycle with the environmental factors
such that they occur at the most profitable time of the year.
How this is achieved is unclear? One possibility is that the
absence of the pineal or of the rhythmic melatonin signal
enhances the sensitivity of the circadian system to light. As
a consequence of this, the amplitude of perceived LD cycle
is amplified which might alter the photoperiodic response
generally seen in terms of the gonadal growth–regression
cycle. Another compelling evidence for the role of pineal in
regulation of hypothalamo–hypophyseal–gonadal (h-h-g)
axis comes from the studies of Ubuka et al. (2005, 2006).
They have shown the effects of melatonin on GnIH
synthesis in male Japanese Quail. GnIH directly inhibits
gonadal development and maintenance by decreasing
gonadotropin synthesis and release (Tsutsui et al 2000;
Ubuka et al. 2006), and the expression of GnIH precursor
mRNA is photoperiodically controlled and influenced by
the melatonin (Ubuka et al. 2005). Further, testicular
regression is not caused by the decrease in GnRH-1 (one
form of gonadotropin-releasing hormone; Foster et al. 1988;
Dawson et al. 2001), which is considered controlling
reproductive functions in birds (Sharp et al. 1990). Ubuka
et al. (2005) suggest that gonadal regression instead occurs
due to increase in the expression and content of the GnIH. It
is therefore likely that the role of pineal/melatonin is more
pronounced in termination of the breeding season, which is
a much more critical event as far as temporal phasing of the
reproductive cycle in relation to the environment is con-
cerned. Incidentally, the majority of investigations done
thus far were focused on determining the role of pineal/
melatonin in photoperiodic induction of gonadal growth. In
view of this, it may be interesting to investigate if pineal/
melatonin is involved in regulation of annual reproductive
cycle of Indian Weaver Birds and of other species, as well
via its actions on processes along the h-h-g axis associated
with termination of the breeding season.
Acknowledgments The experiments described in this article con-
form to Indian laws, and were done using the facility exclusively
generated from the SERC research grant to V.K. by the Department of
Science and Technology (DST), Government of India. The recent
award of DST-IRHPA Center for Excellence on Biological Rhythm
Research which made available resources to us for the preparation of
this article is gratefully acknowledged. We thank both the reviewers
for their helpful comments which improved the manuscript.
Sham operated Pinealectomised
0900 2100 0900 2100 0900 2100 0900 2100 0900
Day
s
12L:12D
LLdim
Onset of
arrhythmicity
**
0900
Fig. 6 Double plotted activity
recordings of a representative
male Indian Weaver Bird
exposed first to 12L:12D and
then released into dim
continuous light (LLdim) in the
month of January, when birds
had small testes and non-
breeding type of beak and
plumage pigmentation. Bar at
the top: Time of day:
0900 hours—lights ON of
12L:12D. Note the abolition of
circadian rhythmicity after a
few cycles in pinealectomized
(right), but not in sham-operated
birds. Asterisk on the right
indicates when pinealectomy or
sham-operation was done. Data
are taken from Rani et al. (2005)
S608 J Ornithol (2007) 148 (Suppl 2):S601–S610
123
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