title: Adrenocortical responses in zebra finches (Taeniopygia guttata): individual variation, repeatability, and relationship to phenotypic quality.
abstract: Although individual variation is a key requirement for natural selection, little is known about the magnitude and patterns of individual variation in endocrine systems or the functional significance of that variation. Here we describe (1) the extent and repeatability of inter-individual variation in adrenocortical responses and (2) its relationship to sex-specific phenotypic quality, such as song duration and frequency and timing of egg laying. We measured adrenocortical responses to a standardized stressor in zebra finches (Taeniopygia guttata) at two life history stages: approximately day 16 (nestlings) and 3 months of age (sexually mature adults). Subsequently, we assessed phenotypic (reproductive) quality of all individuals as adults. Marked inter-individual variation in the adrenocortical response was seen in both sexes and ages, e.g., stress-induced corticosterone ranged from 2.2 to 62.5 ng/mL in nestlings and 5.0-64.0 ng/mL in adults. We found sex differences in (a) inter-individual variation in the adrenocortical response, (b) repeatability, and (c) relationships between corticosterone levels and phenotypic quality. In males, variation in nestling corticosterone was weakly but positively correlated with brood size and negatively correlated with nestling mass (though this relationship was dependent on one individual). There was no significant correlation of adrenocortical responses between two stages in males and adult phenotypic quality was significantly correlated only with adult corticosterone levels. In contrast, in females there was no relationship between nestling corticosterone and brood size or mass but adrenocortical response was repeatable between two stages (r2=0.413). Phenotypic quality of adult females was correlated with nestling baseline and adrenocortical response.
authors.affiliation: Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA. haruka@vt.edu
authors.forename: Haruka
authors.initials: H
authors.lastname: Wada
authors.forename: Katrina G
authors.initials: KG
authors.lastname: Salvante
authors.forename: Christine
authors.initials: C
authors.lastname: Stables
authors.forename: Emily
authors.initials: E
authors.lastname: Wagner
authors.forename: Tony D
authors.initials: TD
authors.lastname: Williams
authors.forename: Creagh W
authors.initials: CW
authors.lastname: Breuner
mesh_terms: D000302:Adrenal Cortex / Q000378:metabolism*; D000367:Age Factors; D000818:Animals; D049628:Body Size; D052284:Clutch Size; D003345:Corticosterone / Q000097:blood*; D005260:Female; D046369:Finches / Q000502:physiology*; D008297:Male; D010641:Phenotype; D012016:Reference Values; D015203:Reproducibility of Results; D012737:Sex Factors; D012741:Sexual Maturation / Q000502:physiology*; D013315:Stress, Psychological / Q000097:blood*; D014156:Transcortin / Q000032:analysis; D014828:Vocalization, Animal / Q000502:physiology
chemical_list: D014156:Transcortin; D003345:Corticosterone