Lifespan heterogeneity reflects intrinsic quality, not trade-offs

Individuals of the same species often display extensive lifespan heterogeneity. However, the factors underlying such heterogeneity remain largely elusive. Here, we examined whether lifespan variation in the naturally short-lived turquoise killifish ( Nothobranchius furzeri ) is caused by reproductive trade-offs. We found that lifespan and reproduction do not trade off: early-life reproductive success positively predicts male lifespan and reflects intrinsic quality. A causal-informed model, where intrinsic quality affects both survival and reproduction, fully recapitulates the empirical data. Together, our results show inter-individual variation in intrinsic quality explains lifespan heterogeneity in a short-lived vertebrate, challenging the view that reproductive costs drive inter-individual lifespan variation.