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 Afro-tropical 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 12.25 h of light and 11.75 h of darkness per day. At intervals of 2.5 to 3.5 weeks, daytime light intensity was changed from bright (12,000 lux at one and 2,000 lux at the other perch) to dim (1,600 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 profiles.
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Acknowledgment
The experiments were carried out at the Max Planck Institute for Ornithology, Andechs, Germany, and comply with German laws. Visits of V.K., S.M., and A.K.T. were supported by a DST–DAAD personnel-based exchange program grant. We are grateful to Dr. Patricia J. DeCoursey and the anonymous reviewers for their helpful comments.
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Professor Dr. E. Gwinner died on 07 September 2004.
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Kumar, V., Rani, S., Malik, S. et al. Daytime light intensity affects seasonal timing via changes in the nocturnal melatonin levels. Naturwissenschaften 94, 693–696 (2007). https://doi.org/10.1007/s00114-007-0243-1
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DOI: https://doi.org/10.1007/s00114-007-0243-1