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THE EVOLUTION OF POSTREPRODUCTIVE LIFE SPAN AS AN INSURANCE AGAINST INDETERMINACY

Authors

  • Thomas Tully,

    1. CNRS UMR 7625, Laboratoire Écologie & Évolution, École Normale Supérieure, 46 rue d’Ulm, 75005 Paris, France
    2. IUFM de Paris, Université Paris 4—Sorbonne, 10 rue Molitor, 75016 Paris, France
    3. E-mail: tully@biologie.ens.fr
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  • Amaury Lambert

    1. CNRS, UMR 7599, Laboratoire de Probabilités et Modèles Aléatoires, Université Pierre et Marie Curie (P6), Case courrier 188, 75252 Paris, Cedex 05, France
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Abstract

Postreproductive life span remains a puzzle for evolutionary biologists. The explanation of increased inclusive fitness through parental care after reproduction that applies for humans is unrealistic for many species. We propose a new selective mechanism, independent of parental care, which relies on the hypothesis that postreproductive life span can evolve as an insurance against indeterminacy: longer life expectancy reduces the risk of dying by chance before the cessation of reproductive activity. We demonstrate numerically that the duration of evolved postreproductive life span is indeed expected to increase with variability in life span duration. An unprecedented assay of 11 strains of the collembola Folsomia candida shows the existence of (1) postreproductive life span in the absence of parental care; (2) genetic variability in mean postreproductive life span and postreproductive life span variability itself; (3) strong genetic correlation between latter traits. This new explanation brings along the novel idea that loose canalization of a trait (here, somatic life span) can itself act as a selective pressure on other traits.

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