title: Epaulet size and current condition in red-winged blackbirds: examining a semistatic signal, testosterone, immune function, and parasites.
abstract: Some sexually selected signals are thought to convey information about the current condition and genetic/epigenetic quality of the individual signaling, including the ability to resist parasites. However, it is unclear whether semistatic sexual signals that develop periodically and remain stable over protracted periods, such as avian breeding plumage, can relate to measures of current condition and health. We examined a semistatic signal (wing epaulet size) in male red-winged blackbirds (Agelaius phoeniceus) during the breeding season and looked for relationships between this trait and circulating testosterone (T), hematocrit, bacteria-killing ability (BKA) of the blood, and the infection status, richness, and abundance of four functional categories of parasite. We found that epaulet size was positively related to circulating levels of T and ectoparasite infections. We found no relationships between T and parasite infections. In adult males there was a negative relationship between T and BKA, whereas in yearling males there was no relationship. We found no evidence for a general reduction in immunocompetence in males with larger epaulets but rather an increase in susceptibility to specific types of parasites. Our results suggest that semistatic signals can be linked to measures of current condition, and we postulate that these relationships are modulated via activity levels related to breeding-season activities.
authors.affiliation: Illinois Natural History Survey, University of Illinois, Urbana-Champaign, Illinois 61820; 2Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California 93106; 3Department of Animal Biology, University of Illinois, Urbana-Champaign, Illinois 61820; 4Department of Neurobiology, Physiology and Behavior, University of California, Davis, California 95616; 5Department of Biology, University of Missouri, St. Louis, Missouri 63121.
authors.forename: Loren
authors.initials: L
authors.lastname: Merrill
authors.forename: Tara E
authors.initials: TE
authors.lastname: Stewart
authors.forename: Paulina L
authors.initials: PL
authors.lastname: González-Gómez
authors.forename: Adrian L
authors.initials: AL
authors.lastname: O'Loghlen
authors.forename: John C
authors.initials: JC
authors.lastname: Wingfield
authors.forename: Vincenzo A
authors.initials: VA
authors.lastname: Ellis
authors.forename: Stephen I
authors.initials: SI
authors.lastname: Rothstein
mesh_terms: D000818:Animals; D005241:Feathers; D007121:Immunocompetence; D008297:Male; D010272:Parasitic Diseases / Q000503:physiopathology*; D010273:Parasitic Diseases, Animal; D046109:Passeriformes / Q000276:immunology / Q000469:parasitology / Q000502:physiology*; D010858:Pigmentation; D012727:Sex Characteristics; D013739:Testosterone / Q000378:metabolism*
chemical_list: D013739:Testosterone