Parental investment and egg yolk lipid composition in gulls

1. Within-clutch variation in parental investment of yolk lipid (including essential fatty acid composition and fat-soluble vitamin content) was inves tigated in whole clutches of three eggs of Lesser Black-backed Gulls, Larus fuscus. 2. Although there were no significant differences between years in egg size or yolk mass among eggs of the same laying order, eggs collected in 1996 h ad significantly lower lipid content than those collected in 1997. 3. In both years third-laid c-eggs were smaller, had a smaller mass of yolk and had significantly lower yolk lipid mass compared with earlier laid (a- and b-) eggs. 4. Despite this lower lipid mass of c-eggs, of the different lipid fraction s only cholesterol content of c-eggs was significantly lower than that of a - or b-eggs. 5. Earlier laid eggs had greater amounts of arachidonic acid in the phospho lipid and cholesterol eater fractions of yolk lipid, and considerably great er quantities of vitamin E and carotenoids. 6. Conversely, levels of linoleic acid and vitamin A were equalized among e ggs of different laying sequence as both these essential nutrients have pri marily systemic roles. 7. The probable effect of increased antioxidant (vitamin E and carotenoid) content of earlier-laid eggs is to enhance embryonic and neonatal growth an d development, reduce susceptibility to pathogens and increase the ability of the embryo to withstand the oxidative stress associated with hatching. 8. The results suggest that there is maternal bias of essential nutrients t o offspring with the highest reproductive value in order to maximize reprod uctive success.