Sibling bullying during infancy does not make wimpy adults.

Despite frequent suggestions that dominance-subordination relationships in infancy can affect subsequent agonistic potential during adult life, to our knowledge no explicit test has been made. Experiments have shown that adverse conditions during early development can have long-term effects on a variety of traits ranging from growth to competitive behaviour. In many vertebrate species, the main social setting in which the infant develops is a sibling group where competition is often mediated by a dominance hierarchy. Here, we show in a long-lived marine bird that subordination to an aggressive sibling throughout infancy does not compromise aggressiveness years later during adult life. Former junior and senior chicks of the blue-footed booby, whose typical brood of two chicks exhibits a consistent dominance-subordination relationship with strong 'trained winner' and 'trained loser' conditioning effects, did not differ in their aggressiveness while defending their nest against a conspecific intruder stimulus. Our results suggest that aggressive subordination and associated food deprivation, poor growth and elevated stress hormone during infancy do not prejudice aggressiveness of adult boobies during at least the first 13 years of life. Development of important traits such as aggressive tendencies may be buffered against the normal and predictable challenges of infancy.