title: Sex differences in leucocyte telomere length in a free-living mammal.
abstract: Mounting evidence suggests that average telomere length reflects previous stress and predicts subsequent survival across vertebrate species. In humans, leucocyte telomere length (LTL) is consistently shorter during adulthood in males than in females, although the causes of this sex difference and its generality to other mammals remain unknown. Here, we measured LTL in a cross-sectional sample of free-living Soay sheep and found shorter telomeres in males than in females in later adulthood (>3 years of age), but not in early life. This observation was not related to sex differences in growth or parasite burden, but we did find evidence for reduced LTL associated with increased horn growth in early life in males. Variation in LTL was independent of variation in the proportions of different leucocyte cell types, which are known to differ in telomere length. Our results provide the first evidence of sex differences in LTL from a wild mammal, but longitudinal studies are now required to determine whether telomere attrition rates or selective disappearance are responsible for these observed differences.
authors.affiliation: Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, The King's Buildings, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Watson
authors.affiliation: Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, The King's Buildings, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.
authors.forename: Ellen J
authors.initials: EJ
authors.lastname: Bird
authors.affiliation: Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, The King's Buildings, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.
authors.forename: Sarah
authors.initials: S
authors.lastname: Underwood
authors.affiliation: Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, The King's Buildings, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.
authors.forename: Rachael V
authors.initials: RV
authors.lastname: Wilbourn
authors.affiliation: Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, The King's Buildings, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Fairlie
authors.affiliation: Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, The King's Buildings, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Watt
authors.affiliation: SynthSys, University of Edinburgh, The King's Buildings, Waddington Building, Max Bourne Crescent, Edinburgh, EH9 3BF, UK.
authors.forename: Eliane
authors.initials: E
authors.lastname: Salvo-Chirnside
authors.affiliation: Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, The King's Buildings, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.
authors.forename: Jill G
authors.initials: JG
authors.lastname: Pilkington
authors.affiliation: Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, The King's Buildings, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.
authors.forename: Josephine M
authors.initials: JM
authors.lastname: Pemberton
authors.affiliation: Moredun Research Institute, Pentlands Science Park, Bush Loan, Midlothian, EH26 0PZ, UK.
authors.forename: Tom N
authors.initials: TN
authors.lastname: McNeilly
authors.affiliation: Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, The King's Buildings, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.
authors.forename: Hannah
authors.initials: H
authors.lastname: Froy
authors.affiliation: Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, The King's Buildings, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK.
authors.forename: Daniel H
authors.identifier: http://orcid.org/0000-0002-9985-0317
authors.initials: DH
authors.lastname: Nussey
mesh_terms: D000818:Animals; D003430:Cross-Sectional Studies; D005260:Female; D007962:Leukocytes; D008297:Male; D012727:Sex Characteristics; D012756:Sheep / Q000235:genetics*; D016615:Telomere / Q000648:ultrastructure*; D059506:Telomere Shortening
keywords: 
  Ovis aries
  ; Soay sheep; granulocyte; lymphocyte; polygyny; sexual selection