View of PHOTOPERIODIC INDUCED RESPONSE CYCLE DURING RAINY SEASON OF STURNUS PAGODARUM

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ACCENT JOURNAL OF ECONOMICS ECOLOGY & ENGINEERING

Peer Reviewed and Refereed Journal, ISSN NO. 2456-1037 Available Online: www.ajeee.co.in/index.php/AJEEE

Vol. 06, Issue 02, February 2021 IMPACT FACTOR: 7.98 (INTERNATIONAL JOURNAL) 46 PHOTOPERIODIC INDUCED RESPONSE CYCLE DURING RAINY SEASON OF STURNUS

PAGODARUM Dr. Arvind Kumar

Deptt. of Zoology, Govt. Degree College Kapoori Govindpur, Saharanpur

Abstract- Adult male birds were procured locally at Meerut (29°N) in mid May 2005. This experiment investigated the nature of the photoinducible phase in relation to rainy season.

Birds were procured from the wild in the last week of May 2005 and acclimatized in the out door aviary. Body mass and testicular volumes were collected at the beginning and at end of the experiment. During experimentation, food (soft and proteinaceous diets) and water were available ad libitum, and were resupplied when the lights were on. The experiment was started on 16 June 2005 i.e. rainy season. First group of photosensitive birds (n=5 each) was exposed to 36h day (L:D=6:30h) and second group was control group, exposed to 24h day (L:D=6:18h) for 12 months. Resonance experiments (also called Nanda-Hamner experiments) consist of a fixed non-stimulatory photophase (4h or 6h) coupled with varying durations of scotophase, resulting in cycles of 24, 36, 48, 60, and 72 h). Animals exposed to 24- or 48- or 72 h cycle length generally exhibit short day responses.

Keywords: Nanda-Hamner experiments, brahminy myna, body mass, testicular volumes 1 INTRODUCTION

In many vertebrates, day length regulates seasonal cycles such as those of body mass and gonad development through induction and termination of physiological processes (Kumar, 1997: Kumar, 2020).

Day length interacts with the endogenous timing mechanism - called the photoperiodic clock – of an individual to decode the time of the year to switch on (photoinduction) physiological mechanisms that underlie a seasonal event (Kumar et al., 2004). The timing of photoinduction sets the timing of the termination of a physiological process (Nicholls et al., 1988). The photoperiodic clock shows features consistent with a circadian rhythm (Singh et al., 2002).

Each day, the circadian photoperiodic rhythm (CPR) is envisaged as passing some 12 hours after dawn through a period of maximum photoinducibility (=

photoinducible phase [фi] of the CPR).

Light falling in this period is read as “long day” and causes photoinduction of seasonal responses. This explains testicular recrudescence and stimulation of other reproduction-associated events during spring and summer in long day breeders. If daily light is short of extending into the фi as during winter months, there is no photoinduction and instead there is recovery of the photosensitivity in photorefractory individuals of many long day breeders (Nicholls et al., 1988).

A number of studies provide evidence that the CPR mediates both the

stimulation of gonadal growth and the termination of post-reproductive refractoriness in photoperiodic birds (Rani and Kumar, 1999; Trivedi et al., 2005).

Resonance experiments constitute one of the most powerful methods widely used to test the circadian rhythm involvement in photoperiodism. Nanda and Hamner first introduced them in 1958. These LD cycles usually consist of a non-stimulatory photophase (6 to 8 h) coupled with varying durations of scotophase (6L: 6 (2n+1) D: where L - photophase, D - scotophase, n - number of multiples of 6D) resulting in cycles of multiples of 12 h, such as 6L:6D, 6L:18D, 6L:30D, 6L:42D, 6L:54D and 6L:66D.

Photoperiodic induction fails to occur in 24 h LD cycle or its multiples (48 h or 72 h). While photoperiodic induction occurs in 12 h cycle and multiples of 24 h plus 12 h. Complete resonance experiments have been performed on house finch (Hamner and Enright, 1967), blackheaded bunting (Tewary and Kumar, 1981), brahminy myna (Kumar and Kumar, 1993; Kumar, 2017) External coincidence model is usually invoked to explain how a circadian rhythm mediates photoperiodism in birds (Pittendrigh, 1972).

Results from most photoperiodic species are consistent with this model (Tewary and Kumar, 1981; Kumar and Kumar, 1993). However, there may be differences in the characteristics of the CPR in order to achieve the species-

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Vol. 06, Issue 02, February 2021 IMPACT FACTOR: 7.98 (INTERNATIONAL JOURNAL) 47 specific response, which is adaptive. This

has not been adequately studied although we know that in general, bird circadian clocks are recognized into weakly and strongly self-sustained oscillator types (Kumar and Follett, 1993). For example in species like Japanese quail (Coturnix c.

Japonica) the photoperiodic pacemaker is weakly self-sustaining and rapidly damps out in the constant condition (Follett et al., 1992). The nature of the photoperiodic clock can be ascertained by how a bird responds to exotic light-dark (LD) cycles.

One such LD cycles is that proposed by Nanda and Hamner (1958) in which exposure of organisms to T=36 h (T = period of the LD cycle; 6L:30D), with controls in T = 24 h (6L:18D), allows alternate light periods falling at two different phases of the CPR. This results in response reflecting the characteristics of the underlying CPR (Kumar and Follett, 1993). For instance, a 6L:30D is non- inductive to Japanese quail that contains weakly self-sustained photoperiodic clock (Follett et al., 1992), but causes full photoperiodic induction in species containing strongly self-sustaining photoperiodic clock (Kumar and Kumar, 1993).

2 MATERIAL AND METHODS

Experiment was performed in the photoperiodic chambers of the laboratory.

During artificial photostimulation in different photoperiods of various experimental series, groups of birds were held in light – tight boxes lit by compact fluorescent tubes (CFL, Phillips) of 14 watt of an intensity of ~ 600 lux at perch level. Automatic time switches (Muller clock) controlled the periods of light and dark. In caged condition, birds were kept in small groups of (size – 45 x 30 x 30 cm) were placed in the photoperiodic box (size – 75 x 70 x 60 cm) for photoperiodic experiments.

All birds were individually weighed on a portable top pan balance to the nearest 0.1g to record the changes in body mass. For this, the birds were individually wrapped in small cotton bag and weighed before being laparotomized.

Testicular volume was calculated from the Bissonnette’s formula (Bissonnette, 1937) i.e. V = 4/3ab², where V is the volume, a is half of the long axis and b is the radius of the testis at its widest point. Results

were analysed using paired student t test.

Significance was always taken at P < 0.05.

Data from these measurements were collected at the beginning and at end of the experiment.

2.1 Experiment

Adult birds were procured locally at Meerut (29°N) in mid February 2005. This experiment investigated the nature of the photoinducible phase in relation to seasons. Birds for the experiment were selected from rainyseason. Under Nanda- Hamner experiments a group of birds (n=5 each) were exposed to a 36 h day (L:D=6:30h), and control exposed to a 24h day (L:D=6:18h) in the seasons mentioned above (fig.1). Observations on body mass and testis size were taken at the beginning, the end and at appropriate intervals during the experiments.

3 RESULT

Result are shown in the figure 1 first group of birds (n=5 each) were exposed to 36h day (L: D=6:30h) and second group was control group, exposed to 24h day (L:D=6:18h) n June (Rainy season) for next 12 months. There was significant change in the body mass in both the groups (1-way RM ANOVA: 6L:18D, F12,36=8.765, P<0.0001 and 6L:30D, F12,36=4.424, P=0.0003). Testis regressed under both photoperiod and there was significant change in the testis volume in both the groups (1-way RM ANOVA:

6L:18D, F12,36=106.2, P<0.0001 and 6L:30D, F12,36=84.88, P<0.0001).

4 DISCUSSION

Hamner (1968) and Murton et al., (1970) had suggested earlier that a circadian rhythm is involved in the termination of photorefractoriness, but their experiments were not conclusive. However, Sansum and King (1975) demonstrated in Gambel’s White-crowned Sparrows (Z. l.

gambelii) that such a rhythm was indeed involved in ending the refractory state. A similar rhythm has recently been discovered in the palearctic Red-headed Bunting (Emberiza bruniceps) Prasad and Tewary (1983).Endogenous circadian rhythms, probably of multiple phylogenetic origin, appear to be involved in time measurement in the photoperiodic responses of a number of avian species (Follett, 1978; Turek and Campbell,

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Vol. 06, Issue 02, February 2021 IMPACT FACTOR: 7.98 (INTERNATIONAL JOURNAL) 48 1979). Comparative studies to data,

however, including one on Black headed Buntings (Tewary and Kumar, 1981), have dealt with the initiation or maintenance of gonadal growth, rather than photorefractoriness (Turek, 1974;

Gwinner and Eriksson, 1977).

The present data (fig.1) In June group mynas were refractory, exposed to 6L:30D did not evoke a long day response and there was no dramatic increase in testis size although body mass was significantly varied over the period of exposure. The conclusions derived from these experiment that brahminy myna possess strong self sustaining circadian clocks produced different photoperiodic responses explained that circadian oscillators governing photoperiodism can be different from those regulating other circadian functions. In general, this interpretation is consistent with the idea of avian circadian system being a multi- oscillatory unit (Kumar et al., 2004).

Misra et al., (2004) have suggested the possibility of two mechanisms, photoperiodism and circannual rhythm generation, being involved simultaneously in regulation of seasonality in birds.

Differential response to exotic light cycle between house sparrow (Passer domesticus) and redheaded bunting (Emberiza bruniceps) photosensitive species, despite their similar circadian oscillatory properties (strong self- sustainment), could suggest a species- specific adaptation of the endogenous clock involved in photoperiodic regulation of avian seasonality (Trivedi et al., 2005).

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