SCHOECH, Stephan J.; Univ. of Memphis: Mechanisms Underlying Behavioral Plasticity in Cooperatively Breeding Birds

Cooperatively breeding is a social system in which individuals express different behaviors consistent with their occupying different within-group roles. Behavioral plasticity in Florida Scrub-Jays is exemplified by a single pair reproducing while other group members help to rear non-descendant young. Two lines of evidence suggest that the divergent behaviors of birds of different status represent phenotypic plasticity rather than a simple ontogenetic progression. First, while most individuals serve as helpers only during their first year, some individuals remain as helpers for two or more years. Second, in cases when the mate of a breeder dies, the surviving individual occasionally �reverts� to helper status. Approximately 4% of the world�s 10,000 species of birds breed cooperatively in one form or another. However, the considerable variance in breeding systems that fall under the umbrella of cooperative breeding makes reaching definitive conclusions about universal hormonal mechanisms responsible for cooperative behaviors difficult. However, endocrine data from Florida Scrub-Jays and other cooperatively breeding species suggest that in some instances, hormonal state can mediate behavioral plasticity. For example, Florida Scrub-Jay helpers do not engage in any of the behaviors typically exhibited during the �sexual stage� of the breeding season (i. e., courtship, copulation, nest building, or incubation), yet after nestlings have hatched during the �parental stage�, helpers engage in alloparental behaviors and provision young in the nest. The reproductive quiescence during the sexual stage is reflected in relatively low plasma levels of sex steroid hormones, whereas their participation during the parental stage is correlated with elevated plasma levels of prolactin.