Keeping Time Under the Midnight Sun: Behavioral and Plasma Melatonin Profiles of Free-Living Lapland Longspurs (Calcarius lapponicus) During the Arctic Summer
Version of Record online: 9 OCT 2012
Copyright © 2012 Wiley Periodicals, Inc.
Journal of Experimental Zoology Part A: Ecological Genetics and Physiology
Volume 319, Issue 1, pages 10–22, January 2013
How to Cite
2012. Keeping time under the midnight sun: Behavioral and plasma melatonin profiles of free-living Lapland longspurs (Calcarius lapponicus) during the arctic summer J. Exp. Zool. 319A:10–22., , , .
- Issue online: 18 DEC 2012
- Version of Record online: 9 OCT 2012
- Manuscript Accepted: 10 SEP 2012
- Manuscript Revised: 12 AUG 2012
- Manuscript Received: 1 JUN 2012
- National Science Foundation. Grant Number: OPP 0817635
Polar environments are characterized by discrete periods of continuous light or darkness during the summer and winter months, respectively. Because the light/dark cycle serves as the primary Zeitgeber to synchronize rhythms of most organisms, its seasonal absence in polar regions poses challenges to the circadian organization of organisms that reside in these environments. Although some species become arrhythmic, others, such as migratory songbirds, are able to maintain an intact diurnal rhythm during polar summer. This suggests that birds may switch to alternative environmental cues, such as daily changes in light intensity and ambient temperature, which may have the potential to reset the biological clock. However, identifying the low-amplitude Zeitgeber that synchronizes rhythms in free-living polar-dwelling animals has been difficult to demonstrate. In this study, we measured behavioral and melatonin profiles of free-living Lapland longspurs (Calcarius lapponicus) near Barrow, Alaska (71°N) during the continuous daylight of summer in the Arctic. Diel cycles in activity and male singing were apparent throughout the polar day with a quiescence period of 4–5 hr starting around 24:00 Alaska Daylight Time. This inactivity corresponded with elevated melatonin profiles. In contrast, territorial aggression of males in response to a conspecific intruder was not dependent upon time-of-day. Diel changes in light intensity and ambient temperature were negatively associated with daily melatonin profiles after taking into account time-of-day effects. These results suggest that photic and thermal cues may act either as alternative Zeitgeber cues, or possibly masking agents. Distinguishing between these two possibilities will require further study. J. Exp. Zool. 319A:10–22, 2013. © 2012 Wiley Periodicals, Inc.