Several hypotheses have been put forward to explain the evolution of senescence. One of the leading hypotheses, the disposable soma hypothesis, predicts a trade-off, whereby early-life investment in reproduction leads to late-life declines in survival (survival senescence). Testing this hypothesis in natural populations is challenging, but important for understanding the evolution of senescence. We used the long-term data set from a contained, predator-free population of individually marked Seychelles warblers (Acrocephalus sechellensis) to investigate how age-related declines in survival are affected by early-life investment in reproduction and early-life environmental conditions. The disposable soma hypothesis predicts that higher investment in reproduction, or experiencing harsh conditions during early life, will lead to an earlier onset, and an increased rate, of senescence. We found that both sexes showed similar age-related declines in late-life survival consistent with senescence. Individuals that started breeding at a later age showed a delay in survival senescence, but this later onset of breeding did not result in a less rapid decline in late-life survival. Although survival senescence was not directly related to early-life environmental conditions, age of first breeding increased with natal food availability. Therefore, early-life food availability may affect senescence by influencing age of first breeding. The disposable soma hypothesis of senescence is supported by delayed senescence in individuals that started breeding at a later age and therefore invested less in reproduction.

SurvivalAbbreviations: Bird = individual identifier; LayYear = year of birth; AFR = age of first reproduction as a dominant; ELGS = early-life group size; ELYearQual = early-life year quality; ELTQ = early-life territory quality; year = year of observation; survival = survived until the next year or notDryad_Survival.xlsxReproductive lifespan and age of first reproductionAbbreviations: BirdID = individual identifier; LayYear = year of birth; AFR = age of first reproduction as a dominant; RLS = reproductive lifespan; event = whether an individual died before the end of the study period; NatalGS = natal group size; NatalYQ = natal year quality; NatalTQ = Natal territory qualityDryad_AFR_RLS.xlsx