Submitted to: Integrative & Comparative Biology
Publication Type: Abstract Only
Publication Acceptance Date: October 29, 2007
Publication Date: N/A
Leptin, a systemic hormone produced by adipocytes or fat cells, has been widely studied in mammals, and is known to play diverse roles in body mass regulation, immune function, reproduction, etc. However we know very little about avian leptin, especially in free-living birds; indeed, this remains a topic of considerable controversy. We investigated variation in plasma leptin levels during reproduction in European starlings (Sturnus vulgaris). Females were sampled opportunistically throughout the breeding season at sequential reproductive stages; after they laid their first egg, at clutch completion, at day 8 of incubation, and between days 11-14 of chick rearing. Data were obtained on body condition and reproductive effort, and plasma leptin was measured using a radioimmunoassay developed for chicken leptin. Plasma leptin levels varied significantly with breeding stage: leptin levels were high during egg-laying (27.6 ± 4.2 ng/ml) and clutch completion (23.8 ± 2.0 ng/ml) then decreased during incubation (13.0 ± 2.0 ng/ml) and chick-rearing (12.0 ± 1.7 ng/ml). We found a weak relationship between plasma leptin and body mass in chick-rearing birds. However, the relationship between plasma leptin and breeding stage was robust controlling for mass and it is unlikely to be driven by mass or changes in body composition (for which we have data in other years). For example, body mass decreased by 14% from egg-laying to clutch completion, but there was no associated change in plasma leptin. Our data suggest that leptin might play a key role in egg production in birds, perhaps involving direct effects on ovarian function (e.g. folliculogenesis) or indirect effects on lipid metabolism (which have been documented in domestic birds and mammals).