title: Divergent patterns of age-dependence in ornamental and reproductive traits in the collared flycatcher.
abstract: Sexual ornaments are predicted to honestly signal individual condition. We might therefore expect ornament expression to show a senescent decline, in parallel with late-life deterioration of other characters. Conversely, life-history theory predicts the reduced residual reproductive value of older individuals will favor increased investment in sexually attractive traits. Using a 25-year dataset of more than 5000 records of breeding collared flycatchers (Ficedula albicollis) of known age, we quantify cross-sectional patterns of age-dependence in ornamental plumage traits and report long-term declines in expression that mask highly significant positive age-dependency. We partition this population-level age-dependency into its between- and within-individual components and show expression of ornamental white plumage patches exhibits within-individual increases with age in both sexes, consistent with life-history theory. For males, ornament expression also covaries with life span, such that, within a cohort, ornamentation indicates survival. Finally, we compared longitudinal age-dependency of reproductive traits and ornamental traits in both sexes, to assess whether these two trait types exhibit similar age-dependency. These analyses revealed contrasting patterns: reproductive traits showed within-individual declines in late-life females consistent with senescence; ornamental traits showed the opposite pattern in both males and females. Hence, our results for both sexes suggest that age-dependent ornament expression is consistent with life-history models of optimal signaling and, unlike reproductive traits, proof against senescence.
authors.affiliation: Edward Grey Institute, Department of Zoology, University of Oxford, United Kingdom. simon.evans@zoo.ox.ac.uk
authors.forename: Simon R
authors.initials: SR
authors.lastname: Evans
authors.forename: Lars
authors.initials: L
authors.lastname: Gustafsson
authors.forename: Ben C
authors.initials: BC
authors.lastname: Sheldon
mesh_terms: D000375:Aging; D000818:Animals; D005260:Female; D008297:Male; D052586:Mating Preference, Animal; D010641:Phenotype; D012098:Reproduction; D012727:Sex Characteristics; D020308:Songbirds / Q000033:anatomy & histology* / Q000502:physiology*; D013548:Sweden