Meeting Abstract

45.2  Saturday, Jan. 5  Corticosterone mediated costs of reproduction facilitate a tradeoff between current and future reproduction. CROSSIN, GT*; PHILLIPS, RA; LATTIN, CR; ROMERO, LM; WILLIAMS, TD; Dalhousie University; British Antarctic Survey; Tufts University; Tufts University; Simon Fraser University gtc@dal.ca

Life-history theory predicts costs of reproduction. One possible mediator of those costs involves the secretion of glucocorticoid hormones, which can be indexed by analyzing concentrations in feathers grown during breeding activity in birds. In the broadest sense, glucocorticoids mediate physiological responses to unpredictable environmental stressors, function as metabolic regulators during predictable events like reproduction, but can also have negative effects (e.g. moult, brood desertion). Here we show that corticosterone (“Cort”) in feathers grown during the reproductive season reflects breeding effort in two Antarctic seabird species (giant petrels, Macronectes spp.). In females of both species, but not males, feather Cort (fCort) was nearly 1.5 fold higher in successful breeders versus failed breeders (those that lost their chick), suggesting a cost of successful reproduction; high fCort levels in females reflect the elevated plasma Cort levels required to support high metabolic demands of successful chick-rearing. Increased fCort and successful breeding also led to delayed moult prior to winter migrations. By monitoring individuals in the following year, we then link fCort levels and pre-migration moult score to subsequent breeding effort. A cost of reproduction, as indexed by high fCort and a delayed initiation of moult, were predictive of deferred breeding in the following year. Cort levels and the timing of moult thus provide a potential mechanism for the tradeoff between current and future reproduction.