Stabilizing survival selection on presenescent expression of a sexual ornament followed by a terminal decline

M. J. P. Simons*, M. Briga, S. Verhulst

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

11 Citations (Scopus)
217 Downloads (Pure)

Abstract

Senescence is a decrease in functional capacity, increasing mortality rate with age. Sexual signals indicate functional capacity, because costs of ornamentation ensure signal honesty, and are therefore expected to senesce, tracking physiological deterioration and mortality. For sexual traits, mixed associations with age and positive associations with life expectancy have been reported. However, whether these associations are caused by selective disappearance and/or within-individual senescence of sexual signals, respectively, is not known. We previously reported that zebra finches with redder bills had greater life expectancy, based on a single bill colour measurement per individual. We here extend this analysis using longitudinal data and show that this finding is attributable to terminal declines in bill redness in the year before death, with no detectable change in presenescent redness. Additionally, there was a quadratic relationship between presenescent bill colouration and survival: individuals with intermediate bill redness have maximum survival prospects. This may reflect that redder individuals over-invest in colouration and/or associated physiological changes, while below-average bill redness probably reflects poorer phenotypic quality. Together, this pattern suggests that bill colouration is defended against physiological deterioration, because of mate attraction benefits, or that physiological deterioration is not a gradual process, but accelerates sharply prior to death. We discuss these possibilities in the context of the reliability theory of ageing and sexual selection.

Original languageEnglish
Pages (from-to)1368-1378
Number of pages11
JournalJournal of Evolutionary Biology
Volume29
Issue number7
DOIs
Publication statusPublished - Jul-2016

Keywords

  • ageing
  • bird
  • carotenoids
  • colouration
  • demography
  • selective disappearance
  • sexual selection
  • zebra finch
  • ZEBRA FINCHES
  • TAENIOPYGIA-GUTTATA
  • MULTIPLE ORNAMENTS
  • SENESCENCE
  • AGE

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