Maternal effects mediated by egg quality in the Yellow-legged Gull Larus michahellis in relation to laying order and embryo sex

Laying sequence-specific patterns of allocation emerged: concentration of carotenoids and vitamin E decreased, while concentrations of androgens increased. Vitamin A, estradiol and corticosterone did not show any change. There was no evidence of sex-specific allocation or covariation of yolk components. Concentrations of carotenoids and vitamins were positively correlated. Egg mass decreased along the laying sequence, and this decrease was negatively correlated with the mean concentrations of carotenoids in clutches, suggesting that nutritionally constrained females lay low quality clutches in terms of carotenoid content. Finally, clutches with smaller decline in antioxidants between first- and last-laid eggs had a larger increase in yolk corticosterone, suggesting that a smaller antioxidant depletion along the laying sequence may entail a cost for laying females in terms of increased stress levels.Since some of the analyzed yolk components (e.g. testosterone and lutein) are known to exert sex-specific phenotypic effects on the progeny in this species, the lack of sex-specific egg allocation by mothers may either result from trade-offs between contrasting effects of different egg components on male and female offspring, or indicate that sex-specific traits are controlled primarily by mechanisms of sexual differentiation, including endogenous hormone production or metabolism of exogenous antioxidants, during embryonic development.In oviparous species, egg size and composition are important components of offspring fitness, with short-term consequences on pre- and early post-natal life-stages as well as enduring effects into adulthood [1-3]. While egg size and composition can be considered as maternal phenotypic traits, the fitness consequences of their variation are typically expressed in the offspring, and these traits are therefore expected to mediate important epigenetic maternal effects [1,2]. Such effects may contribute to adaptively modulate phenotypic variation