title: Genetic and environmental variation in condition, cutaneous immunity, and haematocrit in house wrens.
abstract: BACKGROUND
  Life-history studies of wild bird populations often focus on the relationship between an individual's condition and its capacity to mount an immune response, as measured by a commonly-employed assay of cutaneous immunity, the PHA skin test. In addition, haematocrit, the packed cell volume in relation to total blood volume, is often measured as an indicator of physiological performance. A multi-year study of a wild population of house wrens has recently revealed that those exhibiting the highest condition and strongest PHA responses as nestlings are most likely to be recruited to the breeding population and to breed through two years of age; in contrast, intermediate haematocrit values result in the highest recruitment to the population. Selection theory would predict, therefore, that most of the underlying genetic variation in these traits should be exhausted resulting in low heritability, although such traits may also exhibit low heritability because of increased residual variance. Here, we examine the genetic and environmental variation in condition, cutaneous immunity, and haematocrit using an animal model based on a pedigree of approximately 2,800 house wrens.
  
  
  RESULTS
  Environmental effects played a paramount role in shaping the expression of the fitness-related traits measured in this wild population, but two of them, condition and haematocrit, retained significant heritable variation. Condition was also positively correlated with both the PHA response and haematocrit, but in the absence of any significant genetic correlations, it appears that this covariance arises through parallel effects of the environment acting on this suite of traits.
  
  
  CONCLUSIONS
  The maintenance of genetic variation in different measures of condition appears to be a pervasive feature of wild bird populations, in contradiction of conventional selection theory. A major challenge in future studies will be to explain how such variation persists in the face of the directional selection acting on condition in house wrens and other species.
authors.affiliation: Behavior, Ecology, Evolution and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA. sksakal@ilstu.edu.
authors.forename: Scott K
authors.initials: SK
authors.lastname: Sakaluk
authors.affiliation: Centre for Ecology and Conservation, School of Biosciences, University of Exeter, Penryn, UK. A.Wilson@exeter.ac.uk.
authors.forename: Alastair J
authors.initials: AJ
authors.lastname: Wilson
authors.affiliation: Behavior, Ecology, Evolution and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA. ekbowers@ilstu.edu.
authors.forename: E Keith
authors.initials: EK
authors.lastname: Bowers
authors.affiliation: Department of Biology, Towson University, Towson, MD, USA. sjohnson@towson.edu.
authors.forename: L Scott
authors.initials: LS
authors.lastname: Johnson
authors.affiliation: Department of Biology, Towson University, Towson, MD, USA. bmasters@towson.edu.
authors.forename: Brian S
authors.initials: BS
authors.lastname: Masters
authors.affiliation: Department of Biology, Towson University, Towson, MD, USA. bgjohnson@towson.edu.
authors.forename: Bonnie G P
authors.initials: BG
authors.lastname: Johnson
authors.affiliation: Behavior, Ecology, Evolution and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA. lavogel@ilstu.edu.
authors.forename: Laura A
authors.initials: LA
authors.lastname: Vogel
authors.affiliation: Behavior, Ecology, Evolution and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA. amf226@cornell.edu.|Now at Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA. amf226@cornell.edu.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Forsman
authors.affiliation: Behavior, Ecology, Evolution and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, USA. wrens@ilstu.edu.
authors.forename: Charles F
authors.initials: CF
authors.lastname: Thompson
mesh_terms: D000818:Animals; D000835:Animals, Wild; D005260:Female; D014644:Genetic Variation; D006400:Hematocrit / Q000662:veterinary; D008297:Male; D010375:Pedigree; D012641:Selection, Genetic; D012732:Sex Determination Analysis; D012867:Skin / Q000276:immunology*; D020308:Songbirds / Q000235:genetics* / Q000276:immunology* / Q000502:physiology