Meeting Abstract
Maternal hormones present during embryonic development have the potential to direct and program future offspring phenotypes. Melatonin is a hormone that responds to photoperiod and has a wide range of effects on animal physiology. During development, melatonin neutralizes reactive oxidative species produced during high-metabolic growth periods, and acts as a diffuse neuroendocrine system in early embryonic development. Although melatonin and its enzymatic constituents have been found in egg yolks of domestic birds, their presence and potential ecological and evolutionary significance in free-living birds has not been explored. We measured patterns of melatonin in egg yolks of Franklin’s gull (Leucophaeus pipixcan), a long-distance migratory bird, to understand whether melatonin may be playing a role in patterns of embryonic and post-hatching growth and development. We collected first laid eggs from three Franklin’s gull colonies between 2009 and 2011, and in 2015 we collected 20 full two and three-egg clutches from a single colony for analysis of melatonin. Melatonin was extracted from egg yolks and assayed using an ELISA (enzyme-linked immunosorbent assay). Melatonin was detectable in egg yolks and varied over two-fold across eggs. We measured significant differences in melatonin concentrations in yolk across years and colonies, although within-year variation in melatonin concentrations did not differ among laying dates. Variation in melatonin concentrations across whole clutches indicates there are differences in investment between the initial and final egg of a clutch, which is consistent with previous findings. The presence and variation in yolk melatonin suggests that maternal melatonin could play a role in generating the observed variation in growth and development in these birds and warrants further experimental evaluation.
