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

Abstract

Previous studies show that, in birds, pineal melatonin is important for circadian rhythmicity, and circadian rhythms mediate photoperiodic effects. The effect of pinealectomy or melatonin administration in photoperiodic 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 information. 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 involvement 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.

Molecular basis of photoperiodic control of reproductive cycle in a subtropical songbird, the Indian weaver bird (Ploceus philippinus)

“…Our results confirm that Indian weaver bird undergoes from unstimulated through stimulated and regressed gonadal states on exposure to long days as has been reported earlier (Pavgi et al, 1981;Rani et al, 2007). They further show that changes in expression levels of DIO2, DIO3, GnRH and GnIH genes are linked with photoperiodic induction of testicular cycle.…”

Circadian rhythms are not involved in the regulation of circannual reproductive cycles in a sub-tropical bird, the spotted munia

“…Briefly, birds under local anesthesia were laparotomized and the size of the left testis and ovarian follicle was measured. Such a procedure has no effect on activity rhythms or gonad development cycle in a number of species that we study in our laboratory (Rani et al, 2005;Rani et al, 2007;Singh et al, 2012). Testis volume was calculated using the formula 4/3π ab 2 , where a and b denote half of the long (length) and short (width) axes, respectively.…”

Photoperiodic regulation of seasonal responses in Indian weaver bird (Ploceus philippinus)

“…The color of bill was assessed using a subjective criterion. It was scored in an index of 0-5, as per scheme outlined as follows: 0 -bill straw in color (S), 1 -bill straw in color but with a little tinge of blackness (ratio -SSS:B), 2 -bill slightly blackish in color (ratio -SS:B), 3 -bill straw and black in approximately 50:50 patches (ratio -S:B), 4 -bill black with very little straw patch left (ratio -S:BB) and 5 -bill completely black (B) (Malik et al 2004;Trivedi et al 2006;Rani et al 2007). The plumage color of head and breast of male weaver bird is change during the breeding season; the non-breeding male "female-like" to breeding (nuptial) male bright yellow color.…”

“…Breast = 0 -all "female-like" (no yellow) feathers and 5 -all yellow (no femalelike) 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 (Thapliyal & Saxena 1961;Saxena & Thapliyal 1962;Rani et al 2007). Observations on testicular volume, molt, bill color, and plumage color were made at the beginning and end as well as at appropriate intervals of 2 weeks (molt, bill, and plumage) and 4 weeks (testes).…”