  Maternal investment directly shapes early developmental conditions and
therefore has longterm fitness consequences for the offspring. In oviparous
species prenatal maternal investment is fixed at the time of laying. To ensure
the best survival chances for most of their offspring, females must equip their
eggs with the resources required to perform well under various circumstances,
yet the actual mechanisms remain unknown. Here we describe the blue tit egg
albumen and yolk proteomes and evaluate their potential to mediate maternal
effects. We show that variation in egg composition (proteins, lipids,
carotenoids) primarily depends on laying order and female age. Egg proteomic
profiles are mainly driven by laying order, and investment in the egg proteome
is functionally biased among eggs. Our results suggest that maternal effects on
egg composition result from both passive and active (partly compensatory)
mechanisms, and that variation in egg composition creates diverse biochemical
environments for embryonic development.
