The pineal clock affects behavioral circadian rhythms but not photoperiodic induction in the Indian weaver bird (Ploceus philippinus)

Abstract

We investigated whether pineal is part of the circadian clock system which regulates circadian rhythms of activity and photosensitivity in the Indian weaver bird (Ploceus philippinus). Two experiments were performed. The first experiment examined the induction of testicular growth, and androgen-dependent beak pigmentation and luteinizing hormone (LH)-specific plumage coloration in pinealectomised (pinx) and shamoperated (sham) birds exposed to short day (8 h light: 16 h darkness, 8L:16D) and long day (16L:8D) for 9 months in the late breeding and early regressive phase (October), or the late regressive and preparatory phase (January) of the annual testicular cycle. As expected, short days were non-stimulatory, and long days stimulated testicular growth, beak pigmentation and plumage coloration. There was no difference in the response between pinx and sham birds subjected to short or long days in October, but the response was enhanced in pinx birds that were subjected to long day in January. In the second experiment circadian behavioral rhythms were studied (activity pattern in singly housed birds) in weaver birds first exposed at two different phases of the annual testicular cycle to a stimulatory photoperiod (12L:12D in preparatory phase or 13L:11D in early breeding phase) and then released into dim continuous light (LL dim ). All birds showed synchronization to the light period before and after the pinealectomy; there was no difference in the response between pinx and sham birds. When released into LL dim , sham birds exhibited circadian rhythmicity continuously, whereas pinx birds lost circadian rhythmicity after some cycles. Considered together, these results suggest that circadian clock residing within the pineal gland regulates the circadian rhythm in activity, but not the circadian rhythm involved in photoperiodic induction of the Indian weaver bird.

Photoperiodism, pineal clock and seasonal reproduction in the Indian Weaver Bird (Ploceus philippinus)

“…a-d) also compares some of the results from the two studies on Indian Weaver Birds: those of Balasubramanian 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.…”

“…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).…”

“…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…”

“…; b and d (adapted fromRani et al 2005). Note the difference in photoperiod used in the two studies, but clearly the results ofRani et al …”

Seasonal Plasticity in the Peptide Neuronal Systems: Potential Roles of Gonadotrophin‐Releasing Hormone, Gonadotrophin‐Inhibiting Hormone, Neuropeptide Y and Vasoactive Intestinal Peptide in the Regulation of the Reproductive Axis in Subtropical Indian Weaver Birds

“…Then, they were moved indoors (2.02 × 1.69 × 2.69 m) and exposed to short days (8 : 16 h light/dark cycle; 8L : 16D) at constant temperature (24.0 ± 2.0 °C) until the beginning of the experiment. In short days, weaver birds remain unstimulated and maintain sensitivity to long photoperiod stimulation . At the beginning of the experiment, birds were distributed in two groups of eight each and housed in cages (45 × 31 × 41 cm; n = 4 per cage) kept in separate photoperiodic boxes.…”