Context-dependent effects of yolk XXXX on nestling growth and immune function in a multibrooded passerine.

@entity7571 @entity650 @entity3800 @entity342
UNASSIGNED: Female birds may adjust their offspring phenotype to the specific requirements of the environment by differential allocation of physiologically active substances into yolks, such as @entity3800 . Yolk @entity3800 have been shown to accelerate embryonic development, growth rate and competitive ability of nestlings, but they can also entail immunological costs. The balance between costs and benefits of @entity342 allocation is expected to depend on nestling environment. We tested this hypothesis in a multibrooded passerine, the spotless starling, Sturnus unicolor. We experimentally manipulated yolk @entity342 levels using a between-brood design and evaluated its effects on nestling development, survival and immune function. Both in first and replacement broods, the embryonic development period was shorter for @entity342 -treated chicks than controls, but there were no differences in second broods. In replacement broods, @entity342 -treated chicks were heavier and larger than those hatched from control eggs, but this effect was not observed in the other breeding attempts. @entity342 exposure reduced survival with respect to controls only in second broods. Regarding immune function, we detected nonsignificant trends for @entity342 treatment to activate two important components of innate and adaptive immunity ( @entity650 and @entity7571 levels, respectively). Similarly, @entity342 -treated chicks showed greater lymphocyte proliferation than controls in the first brood and an opposite trend in the second brood. Our results indicate that yolk @entity342 effects on nestling development and immunity depend on the environmental conditions of each breeding attempt. Variation in maternal @entity342 allocation to eggs could be explained as the result of context-dependent optimal strategies to maximize offspring fitness.
