Maternally derived androgens and antioxidants in bird eggs: complementary but opposing effects?

Maternally derived traits, such as within-clutch variation in the amount of testosterone deposited in egg yolks, may have profound effects on offsprin g fitness. Offspring with elevated levels of testosterone may benefit from increased competitive ability through effects on aggression and growth rate . However, elevated levels of testosterone are also associated with costs o f increased peroxidative damage from free radicals and consequent oxidative stress. Diet-derived antioxidants, such as vitamin E and various carotenoi ds, provide protection against the deleterious effects of oxidative stress. Here we show that within-clutch variation in yolk testosterone is the oppo site to that of yolk antioxidant concentration in the lesser black-backed g ull Larus fuscus. We provide evidence that suggests that these two direct m aternal effects are, in fact, complementary and, in conjunction with an ind irect maternal effect (the onset of incubation), may provide an adaptive me chanism for parental favoritism in response to environmental variability. T he potential implications of these findings with respect to previous invest igations on variation in yolk testosterone concentrations and on the unders tanding of intrafamilial dynamics are discussed.