title: Male-biased sex allocation in ageing parents; a longitudinal study in a long-lived seabird.
abstract: Optimal sex allocation is frequency-dependent, but senescence may cause behaviour at old age to be suboptimal. We investigated whether sex allocation changes with parental age, using 16 years of data comprising more than 2500 molecularly sexed offspring of more than 600 known-age parents in common terns (Sterna hirundo), slightly sexually size-dimorphic seabirds. We decomposed parental age effects into within-individual change and sex allocation-associated selective (dis)appearance. Individual parents did not differ consistently in sex allocation, but offspring sex ratios at fledging changed from female- to male-biased as parents aged. Sex ratios at hatching were not related to parental age, suggesting sons to outperform daughters after hatching in broods of old parents. Our results call for the integration of sex allocation theory with theory on ageing and demography, as a change in sex allocation with age per se will cause the age structure of a population to affect the frequency-dependent benefits and the age-specific strength of selection on sex allocation.
authors.affiliation: Institute of Avian Research 'Vogelwarte Helgoland', An der Vogelwarte 21, 26386, Wilhelmshaven, Germany oscarvedder@hotmail.com.
authors.forename: Oscar
authors.identifier: 0000-0003-4689-8568
authors.initials: O
authors.lastname: Vedder
authors.affiliation: Institute of Avian Research 'Vogelwarte Helgoland', An der Vogelwarte 21, 26386, Wilhelmshaven, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Bouwhuis
authors.affiliation: tier3 solutions GmbH, Kolberger Strasse 61, 51381 Leverkusen, Germany.
authors.forename: María M
authors.initials: MM
authors.lastname: Benito
authors.affiliation: Institute of Avian Research 'Vogelwarte Helgoland', An der Vogelwarte 21, 26386, Wilhelmshaven, Germany.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Becker
mesh_terms: D000375:Aging; D000818:Animals; D046091:Charadriiformes; D005260:Female; D008137:Longitudinal Studies; D008297:Male; D012744:Sex Ratio
keywords: parental age; senescence; sex ratio; sex-biased mortality; sexual size dimorphism