title: The relationship of telomere length to baseline corticosterone levels in nestlings of an altricial passerine bird in natural populations.
abstract: BACKGROUND
  Environmental stressors increase the secretion of glucocorticoids that in turn can shorten telomeres via oxidative damage. Modification of telomere length, as a result of adversity faced early in life, can modify an individual's phenotype. Studies in captivity have suggested a relationship between glucocorticoids and telomere length in developing individuals, however less is known about that relationship in natural populations.
  
  
  METHODS
  In order to evaluate the effect of early environmental stressors on telomere length in natural populations, we compared baseline corticosterone (CORT) levels and telomere length in nestlings of the same age. We collected blood samples for hormone assay and telomere determination from two geographically distinct populations of the Thorn-tailed Rayadito (Aphrastura spinicauda) that differed in brood size; nestlings body mass and primary productivity. Within each population we used path analysis to evaluate the relationship between brood size, body mass, baseline CORT and telomere length.
  
  
  RESULTS
  Within each distinct population, path coefficients showed a positive relationship between brood size and baseline CORT and a strong and negative correlation between baseline CORT and telomere length. In general, nestlings that presented higher baseline CORT levels tended to present shorter telomeres. When comparing populations it was the low latitude population that presented higher levels of baseline CORT and shorter telomere length.
  
  
  CONCLUSIONS
  Taken together our results reveal the importance of the condition experienced early in life in affecting telomere length, and the relevance of integrative studies carried out in natural conditions.
authors.affiliation: Departamento de Ecología y Biodiversidad, Facultad de Ecologíam y Recursos Naturales, Universidad Andres Bello, República 440, Santiago, Chile.
authors.forename: Verónica
authors.initials: V
authors.lastname: Quirici
authors.affiliation: Escuela de Medicina Veterinaria, Talca, Facultad de Recursos Naturales y Medicina Veterinaria, Universidad Santo Tomás, Av. Carlos Schorr 255, Talca, Maule Chile.
authors.forename: Claudia Jimena
authors.initials: CJ
authors.lastname: Guerrero
authors.affiliation: Department of Neurobiology, Physiology and Behavior, University of California, One Shields Avenue, Davis, CA 95616 USA.
authors.forename: Jesse S
authors.initials: JS
authors.lastname: Krause
authors.affiliation: Department of Neurobiology, Physiology and Behavior, University of California, One Shields Avenue, Davis, CA 95616 USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Wingfield
authors.affiliation: Instituto de Ecología y Biodiversidad and Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile.
authors.forename: Rodrigo A
authors.initials: RA
authors.lastname: Vásquez
keywords: Brood size; Latitudinal gradient; Thorn-tailed rayadito; qPCR