Fat and Migration: Relationship Between Seasonal Regulation of Adipokines and Behavior
Open Access
- Author:
- Stuber, Erica
- Graduate Program:
- Ecology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 18, 2011
- Committee Members:
- Paul Allen Bartell, Thesis Advisor/Co-Advisor
Paul Allen Bartell, Thesis Advisor/Co-Advisor - Keywords:
- circadian
circannual
migration
behavior
white-throated sparrow
migration
Biological clock
adipokine
adiponectin
visfatin - Abstract:
- Migration events and associated changes in an individual’s behavior patterns occur on a seasonal basis, and are regulated by both circadian and circannual clocks. Although the effects of biological clocks on physiology and behavior are readily observable, their mechanisms and pathways are only slowly being detailed. Certain adipokines, signaling proteins secreted by adipose tissue, including adiponectin and visfatin, may be important to timekeeping systems and act as signals of body condition influencing migratory decisions. Although these adipokines have been investigated in mammals, very few studies have utilized avian species, and currently no work has been published regarding Passerines. Our objectives were to examine circulating levels of both adiponectin and visfatin and to explore potential relationships between these adipokines and the seasonal transition between the non-migratory and migratory life history stages. Captive white-throated sparrows were monitored, under constant photoperiod to rule out the influence of changing light:dark ratios, for changes in plasma levels of the two adipokines across a 24 hour period during the migratory and non-migratory stages. Examination of plasma adiponectin levels using Western blotting revealed that migrating individuals display different circadian patterns of plasma adiponectin compared with non-migrating individuals, which suggests a change in a biological clock regulating adipokine levels. Correlative evidence reveals a strong relationship between plasma adiponectin levels and amount of body fat and nighttime activity in migrating individuals, and mixed effects modeling estimates a reduction in high molecular weight adiponectin of approximately half in migrating individuals. Enzyme-linked immunosorbent assays for visfatin concentration revealed a reduction of approximately 20% in plasma visfatin of migrating individuals. Although this seasonal reduction may be regulated by a circannual clock, we did not detect a circadian rhythm in plasma concentration in either non-migrating or migrating birds. Plasma visfatin did not vary with subcutaneous body fat. Collectively, the results of these studies provide evidence that seasonal or daily differences in signal from adipokines may provide individuals with physiological information regarding fat deposits and might underlie the seasonal behavioral changes necessary for migration.