title: Regulation of the HPA axis is related to song complexity and measures of phenotypic quality in song sparrows.
abstract: Regulation of the hypothalamic-pituitary-adrenal (HPA) axis is a key component of the vertebrate stress response. Prior studies have found that variation in HPA responses were correlated to measures of fitness and physiological condition. In addition, sexually-selected traits have also been found to correlate to measures of condition. The proximate mechanisms responsible for such covariation between sexually selected traits and measures of quality are unclear, but could involve variation in HPA regulation. We investigated whether HPA activity is related to song complexity, body size/condition and leukocyte profiles in wild male song sparrows (Melospiza melodia). We characterized three aspects of HPA activity: 1) response to restraint stress; 2) negative feedback, assessed by the ability of exogenous dexamethasone to suppress corticosterone levels; and 3) adrenal sensitivity to exogenous adrenocorticotropic hormone (ACTH). Birds with lower responses to restraint stress had more complex song and more heterophils and higher heterophil to lymphocyte (H:L) ratios. Birds with more effective negative feedback were larger and had fewer heterophils and lower H:L ratios, suggesting lower levels of physiological stress or infection. We observed no relationship between adrenal sensitivity to exogenous ACTH and any of the factors. These findings illustrate important relationships between HPA activity, song complexity, and morphological and physiological traits. Song complexity may thus provide receivers with information about the ability of the singer to cope with stressors.
authors.affiliation: Department of Biology, University of Western Ontario, London, Ontario, Canada. kschmi5@uwo.ca
authors.forename: Kim L
authors.initials: KL
authors.lastname: Schmidt
authors.forename: Ainsley A
authors.initials: AA
authors.lastname: Furlonger
authors.forename: Janet M
authors.initials: JM
authors.lastname: Lapierre
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: MacDougall-Shackleton
authors.forename: Scott A
authors.initials: SA
authors.lastname: MacDougall-Shackleton
mesh_terms: D000302:Adrenal Cortex / Q000187:drug effects / Q000502:physiology; D000324:Adrenocorticotropic Hormone / Q000097:blood / Q000494:pharmacology; D000819:Animal Communication; D000818:Animals; D049628:Body Size; D001835:Body Weight / Q000502:physiology; D003346:Corticotropin-Releasing Hormone / Q000097:blood; D003907:Dexamethasone; D025461:Feedback, Physiological / Q000187:drug effects; D005938:Glucocorticoids / Q000097:blood; D006304:Health Status; D006854:Hydrocortisone / Q000097:blood; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology*; D007118:Immunoassay; D007958:Leukocyte Count; D008297:Male; D010641:Phenotype; D010809:Physical Fitness; D012149:Restraint, Physical; D046370:Sparrows / Q000502:physiology*; D013315:Stress, Psychological / Q000097:blood; D014828:Vocalization, Animal / Q000502:physiology*
chemical_list: D005938:Glucocorticoids; D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone; D006854:Hydrocortisone