Data from: Covariation in life-history traits: differential effects of diet on condition, hormones, behavior and reproduction in genetic finch morphs

The relative contribution of genetic and environmental factors in
determining variation in life-history traits is of central interest to
evolutionary biologists, but the physiological mechanisms underlying these
traits are still poorly understood. Here we experimentally demonstrate
opposing effects of nutritional stress on immune function, endocrine
physiology, parental care and reproduction between red and black
head-color morphs of the Gouldian finch (Erythrura gouldiae). Although
body condition of black morphs was largely unaffected by diet
manipulation, red birds were highly sensitive to dietary changes,
exhibiting considerable within-individual changes in condition and immune
function. Consequently, nutritionally stressed red birds delayed breeding,
produced smaller broods and reared fewer and lower-quality foster
offspring than black morphs. Differences in offspring quality were largely
due to morph-specific differences in parental effort; red morphs reduced
parental provisioning, whereas black morphs adaptively elevated their
provisioning effort to meet the increased nutritional demands of their
foster brood. Nutritionally stressed genetic morphs also exhibited
divergent glucocorticoid responses. Black morphs showed reduced
corticosterone-binding globulin (CBG) concentrations and increased levels
of free corticosterone, whereas red morphs exhibited reduced free
corticosterone levels and elevated CBG concentrations. These opposing
glucocorticoid responses highlight intrinsic differences in endocrine
sensitivities and plasticity between genetic morphs, which may underlie
the morph-specific differences in condition, behavior and reproduction,
and thus ultimately contribute to the evolution and maintenance of color
polymorphism.