Abstract
Day length regulates annual reproductive cycle in many birds including subtropical Indian Weaver birds (Ploceus philippinus). We investigated whether light intensity modulated the effects of the duration of photoperiod in inducing testicular recrudescence- regression cycle, and whether such effects are influenced by the seasons. Two experiments were performed in which Weaver birds were exposed to near threshold and long photoperiods at different light intensities at two times of the year. In experiment 1, Weaver birds were exposed to 11.5 L:12.5 D, 12 L:12 D and 13 L:11 D photoperiods with light intensity 0.04 and 3.4 Wm−2 for a period of 40 weeks, beginning in May (pre-breeding season). Experiment 2 compared light intensity effects on photoperiodic induction in two different seasons, and differed from the experiment 1 in using a different grade of light intensities. Weaver birds were exposed to 11.5 L:12.5 D, 12 L:12 D and 13 L:11 D at 0.05 and 2.1 Wm−2 light intensity for 24 weeks, beginning in April (pre-breeding season) and September (post-breeding season). Observations on testis size and wing primaries molt were recorded weekly (molt) or at 4-week intervals (testes). There was a significant effect of light intensity on photoperiodic induction of testicular growth in birds exposed to 13 h, but not to 11.5- and 12 h photoperiods. Further, testis recrudescence under a stimulatory photoperiod was faster in birds exposed during pre-breeding, compared to post-breeding. Thus, light intensity influences the rate of testicular maturation and molt, but does not alter the critical day length for photoperiodic induction in Indian Weaver birds. This may be adaptive for birds in using light intensity to modulate the rates of their physiological processes as needed in the wild.
Zusammenfassung
Lichtintensität verändert die stimulierenden Effekte langer Photoperioden, verändert aber nicht die kritische Photoperiode bei Indischen Webervögeln ( Ploceus philippinus )
Die Tageslänge reguliert den jährlichen Reproduktionszyklus vieler Vogelarten inklusive subtropischer indischer Webervögel (Ploceus philippinus). Wir untersuchten, inwiefern die Lichtintensität die Effekte der Länge der Photoperiode hinsichtlich der Induzierung des testikulären Aufbau- und Rückbildungszyklus modifiziert und ob solche Effekte von den Jahreszeiten beeinflusst werden. Zwei Experimente wurden durchgeführt, bei denen Webervögel nahe dem Schwellenwert und langen Photoperioden bei unterschiedlichen Lichtintensitäten zu zwei unterschiedlichen Zeiten im Jahr ausgesetzt wurden. In Experiment 1 wurden Webervögel 11.5 L: 12.55 D, 125 L: 125 D und 135 L: 115 D Photoperioden mit Lichtintensitäten von 0.04 und 3.4 Wm−2 über einen Zeitraum von 40 Wochen ab Anfang Mai (Vorbrutphase) ausgesetzt. Experiment 2 vergleicht die Effekte der Lichtintensität auf die photoperiodische Induzierung zu zwei verschiedenen Jahreszeiten und unterscheidet sich von Experiment 1 im unterschiedlichen Grad der Lichtintensitäten. Webervögel wurden 11.55 L:12.55 D, 125 L:125 D und 135 L:115 D bei Lichtintensitäten von 0.05 und 2.1 Wm−2 über 24 Wochen im April (Vorbrutzeit) und im September (Nachbrutzeit) ausgesetzt. Hodengröße und Handschwingenmauser wurden wöchentlich (Mauserstadium) oder 4-wöchentlich (Hoden) erfasst. Es gab einen signifikanten Effekt der Lichtintensität auf die photoperiodische Induzierung des Hodenwachstums bei Vögeln, die 13 Stunden, aber nicht 11,5 und 12 Stunden Tageslänge hatten. Darüber hinaus erfolgte das Hodenwachstum unter stimulierender Photoperiode schneller bei Vögeln in der Vorbrutzeit im Vergleich zur Nachbrutzeit. Damit beeinflusst die Lichtintensität die Rate der testikulären Reifung und Mauser, verändert jedoch nicht die entscheidende Tageslänge für eine photoperiodische Induzierung bei Webervögeln. Dies könnte eine Anpassungsfähigkeit von Vögeln sein, die die Lichtintensität nutzen, um das Tempo ihrer physiologischen Prozesse entsprechend zu modifizieren.
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Acknowledgments
The study was funded by generous research grants from the Department of Science and Technology, New Delhi, India through research funding (SR/SO/AS-36/2006 and SR/SO/AS-70/2011) to SKB. We also thank Chief Wildlife Warden, Department of Forests and Wildlife, Lucknow, Uttar Pradesh for permitting us to work on this species.
Ethical standard
The experiments were carried out as per approval and guidelines of Institutional Animal Ethics Committee (IAEC), Department of Zoology, Ch. Charan Singh University, Meerut, India.
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Communicated by L. Fusani.
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Bhardwaj, S.K., Pandey, R.K. Light intensity alters the stimulatory effects of long photoperiod, but does not alter critical photoperiod in the Indian Weaver Bird (Ploceus philippinus). J Ornithol 156, 223–229 (2015). https://doi.org/10.1007/s10336-014-1118-9
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DOI: https://doi.org/10.1007/s10336-014-1118-9