title: Repeated stressors in adulthood increase the rate of biological ageing.
abstract: BACKGROUND
  Individuals of the same age can differ substantially in the degree to which they have accumulated tissue damage, akin to bodily wear and tear, from past experiences. This accumulated tissue damage reflects the individual's biological age and may better predict physiological and behavioural performance than the individual's chronological age. However, at present it remains unclear how to reliably assess biological age in individual wild vertebrates.
  
  
  METHODS
  We exposed hand-raised adult Eurasian blackbirds (Turdus merula) to a combination of repeated immune and disturbance stressors for over one year to determine the effects of chronic stress on potential biomarkers of biological ageing including telomere shortening, oxidative stress load, and glucocorticoid hormones. We also assessed general measures of individual condition including body mass and locomotor activity.
  
  
  RESULTS
  By the end of the experiment, stress-exposed birds showed greater decreases in telomere lengths. Stress-exposed birds also maintained higher circulating levels of oxidative damage compared with control birds. Other potential biomarkers such as concentrations of antioxidants and glucocorticoid hormone traits showed greater resilience and did not differ significantly between treatment groups.
  
  
  CONCLUSIONS
  The current data demonstrate that repeated exposure to experimental stressors affects the rate of biological ageing in adult Eurasian blackbirds. Both telomeres and oxidative damage were affected by repeated stress exposure and thus can serve as blood-derived biomarkers of biological ageing.
authors.affiliation: Max Planck Institute for Ornithology, Evolutionary Physiology Group, Am Obstberg 1, 78315 Radolfzell, Germany ; Department of Biology, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany.
authors.forename: Michaela
authors.initials: M
authors.lastname: Hau
authors.affiliation: Department of Biology, Bucknell University, Lewisburg, PA 17837 USA.
authors.forename: Mark F
authors.initials: MF
authors.lastname: Haussmann
authors.affiliation: Max Planck Institute for Ornithology, Evolutionary Physiology Group, Am Obstberg 1, 78315 Radolfzell, Germany ; Department of Biological Sciences, North Dakota State University, 1340 Bolley Drive, Fargo, ND 58202 USA.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Greives
authors.affiliation: Department of Biology, Bucknell University, Lewisburg, PA 17837 USA.
authors.forename: Christa
authors.initials: C
authors.lastname: Matlack
authors.affiliation: Department of Biology, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium ; University of Glasgow, Institute of Biodiversity, Animal Health & Comparative Medicine, Glasgow, QG12 8Q UK.
authors.forename: David
authors.initials: D
authors.lastname: Costantini
authors.affiliation: Max Planck Institute for Ornithology, Evolutionary Physiology Group, Am Obstberg 1, 78315 Radolfzell, Germany ; Department of Biology, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Quetting
authors.affiliation: Max Planck Institute for Ornithology, Evolutionary Physiology Group, Am Obstberg 1, 78315 Radolfzell, Germany ; Department of Biological Sciences, 4092B Derring Hall, Virginia Tech, Blacksburg, VA 24061-0406 USA.
authors.forename: James S
authors.initials: JS
authors.lastname: Adelman
authors.affiliation: Department of Biology, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany ; Max Planck Institute for Ornithology, Department of Migration and Immuno-ecology, Am Obstberg 1, 78315 Radolfzell, Germany ; Departamento de Biologia, Centro de Ciências Biológicas e da Saúde, Universidade Federal do Maranhão, Campus do Bacanga, São Luís, Maranhão Brazil.
authors.forename: Ana Catarina
authors.initials: AC
authors.lastname: Miranda
authors.affiliation: Department of Biology, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany ; Max Planck Institute for Ornithology, Department of Migration and Immuno-ecology, Am Obstberg 1, 78315 Radolfzell, Germany.
authors.forename: Jesko
authors.initials: J
authors.lastname: Partecke
keywords: Biomarker; Eurasian blackbird; Glucocorticoid; Oxidative stress; Repeated stressors; Telomere