Data from: Context-dependent effects of yolk androgens on nestling growth and immune function in a multibrooded passerine

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 androgens. Yolk
androgens 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 androgen
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 androgen 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 androgen-treated chicks than
controls, but there were no differences in second broods. In replacement
broods, androgen-treated chicks were heavier and larger than those hatched
from control eggs, but this effect was not observed in the other breeding
attempts. Androgen exposure reduced survival with respect to controls only
in second broods. Regarding immune function, we detected nonsignificant
trends for androgen treatment to activate two important components of
innate and adaptive immunity (IL-6 and Ig-A levels, respectively).
Similarly, androgen-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 androgen effects on nestling
development and immunity depend on the environmental conditions of each
breeding attempt. Variation in maternal androgen allocation to eggs could
be explained as the result of context-dependent optimal strategies to
maximize offspring fitness.