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Title: Variation in plasma leptin-like immunoreactivity in free-living European starlings (Sturnus vulgaris)

item KORDONOWY, LAUREN - Simon Fraser University
item McMurtry, John
item WILLIAMS, TONY - Simon Fraser University

Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2009
Publication Date: 3/1/2010
Citation: Kordonowy, L.L., Mcmurtry, J.P., Williams, T.D. 2010. Variation in plasma leptin-like immunoreactivity in free-living european starlings (Sturnus vulgaris). General and Comparative Endocrinology. 166(1):47-53.

Interpretive Summary: Leptin, a hormone of fat cells, has been shown to have diverse physiological roles, ranging from regulation of feeding behaviour and body weight to effects on reproductive and immune functions, mainly in mammals. Much less is known about the factors influencing leptin production and its functions in birds, especially whether season influences the previous. Nothing is known about leptin production during reproductive and non-reproductive seasons in free-living birds. This study investigated seasonal changes in leptin at different stages of breeding and in non-breeders. Results of this study suggests that the relationship between circulating leptin and body mass is not as evident as in captive birds and mammals, but that seasonal variation in blood leptin is highly related to reproductive stage and season of the year. The results of this study will be of interest to other scientists.

Technical Abstract: Leptin, a protein hormone secreted by fat cells, is best known for its role as an adiposity signal; however, leptin has diverse physiological roles ranging from regulation of feeding behavior and body weight, to effects on reproduction and immune function. Although leptin has been extensively studied in mammals, purported avian leptin remains highly controversial, and studies have focused on captive or domesticated species. In this study, we describe changes in plasma leptin-like immunoreactivity during the reproductive and non-reproductive seasons in free-living female European starlings (Sturnus vulgaris). Plasma leptin-like immunoreactivity was high during egg-laying (27.8 ± 2.4 ng/mL) and clutch completion (23.8 ± 1.6 ng/mL), decreased during incubation (13.0 ± 1.6 ng/mL) and chick-rearing (12.0 ± 1.3 ng/mL), and was elevated in non-breeders in November (23.7 ± 1.1 ng/mL). Although there was marked and consistent variation in total body mass and body composition with breeding stage and season in this population, patterns of variation in plasma leptin-like immunoreactivity did not parallel changes in body mass or body composition. Our findings demonstrate both reproductive stage and seasonal variation in plasma leptin-like immunoreactivity, which are disparate to patterns of change in body mass and body composition, suggesting that the relationship between plasma leptin-like immunoreactivity and body mass reported for captive birds and mammals does not hold for free-living European starlings. Furthermore, in the context of research linking putative avian leptin with reproduction, we discuss whether elevated estradiol levels during egg-formation could be responsible for the high plasma leptin-like immunoreactivity we found during egg-laying.