Authors: Vinod Kumar Sangeeta Rani Shalie Malik Amit K Trivedi Ingrid Schwabl Barbara Helm Eberhard Gwinner
Publish Date: 2007/04/04
Volume: 94, Issue: 8, Pages: 693-696
Abstract
Daytime light intensity can affect the photoperiodic regulation of the reproductive cycle in birds The actual way by which light intensity information is transduced is however unknown We postulate that transduction of the light intensity information is mediated by changes in the pattern of melatonin secretion This study therefore investigated the effects of high and low daytime light intensities on the daily melatonin rhythm of Afrotropical stonechats Saxicola torquata axillaris in which seasonal changes in daytime light intensity act as a zeitgeber of the circannual rhythms controlling annual reproduction and molt Stonechats were subjected to light conditions simulated as closely as possible to native conditions near the equator Photoperiod was held constant at 1225 h of light and 1175 h of darkness per day At intervals of 25 to 35 weeks daytime light intensity was changed from bright 12000 lux at one and 2000 lux at the other perch to dim 1600 lux at one and 250 lux at the other perch and back to the original bright light Daily plasma melatonin profiles showed that they were linked with changes in daytime light intensity Nighttime peak and total nocturnal levels were altered when transitions between light conditions were made and these changes were significant when light intensity was changed from dim to bright We suggest that daytime light intensity could affect seasonal timing via changes in melatonin profilesThe experiments were carried out at the Max Planck Institute for Ornithology Andechs Germany and comply with German laws Visits of VK SM and AKT were supported by a DST–DAAD personnelbased exchange program grant We are grateful to Dr Patricia J DeCoursey and the anonymous reviewers for their helpful comments
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