Eggs are 'multivariate' in that they contain multiple maternally-derived egg components (e.g. hormones, antibodies, mRNA, antioxidants) which are thought to influence offspring phenotype. However, most studies have focused on single egg components (most often yolk testosterone, or corticosterone), and on short-term effects. Here we simultaneously manipulated two egg components, maternally-derived antibodies (MAb) and yolk testosterone to assess potential synergistic or antagonistic effects on offspring phenotype from hatching to sexual maturity. We used lipopolysaccharide treatment to generate a secondary immune response in female zebra finches (Taeniopygia guttata), which produced clutches of eggs with high (LPS-treated) or low (control) MAb. We then used a split design manipulating yolk testosterone within clutches of high- and low-MAb eggs using in ovo egg injection. We investigated a) short-term effects of experimental manipulation of both egg components at 30 days post-hatching on chick growth and immune function at fledging, and b) long-term effects at sexual maturity (> 90 days post-hatching) on phenotypic quality of i/ males (sons) using standardise mating trials (courtship, song rate, etc); ii/ females (daughters) by measuring reproductive traits during breeding (egg size, clutch size etc), and iii/ cell-mediated and humoral immunity in both sexes.
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