title: Interaction mortality: senescence may have evolved because it increases lifespan.
abstract: Given an extrinsic challenge, an organism may die or not depending on how the threat interacts with the organism's physiological state. To date, such interaction mortality has been only a minor factor in theoretical modeling of senescence. We describe a model of interaction mortality that does not involve specific functions, making only modest assumptions. Our model distinguishes explicitly between the physiological state of an organism and potential extrinsic, age-independent threats. The resulting mortality may change with age, depending on whether the organism's state changes with age. We find that depending on the physiological constraints, any outcome, be it 'no senescence' or 'high rate of senescence', can be found in any environment; that the highest optimal rate of senescence emerges for an intermediate physiological constraint, i.e. intermediate strength of trade-off; and that the optimal rate of senescence as a function of the environment is driven by the way the environment changes the effect of the organism's state on mortality. We conclude that knowledge about the environment, physiology and their interaction is necessary before reasonable predictions about the evolution of senescence can be made.
authors.affiliation: Max Planck Research Group 'Modeling the Evolution of Aging, Max Planck Institute for Demographic Research, Rostock, Germany; Leyden Academy on Vitality and Ageing, Leiden, The Netherlands.
authors.forename: Maarten J
authors.initials: MJ
authors.lastname: Wensink
authors.affiliation: Max Planck Research Group 'Modeling the Evolution of Aging, Max Planck Institute for Demographic Research, Rostock, Germany.
authors.forename: Tomasz F
authors.initials: TF
authors.lastname: Wrycza
authors.affiliation: Max Planck Research Group 'Modeling the Evolution of Aging, Max Planck Institute for Demographic Research, Rostock, Germany; Max-Planck Odense Center on the Biodemography of Aging, University of Southern Denmark, Odense M, Denmark.
authors.forename: Annette
authors.initials: A
authors.lastname: Baudisch
mesh_terms: D005075:Biological Evolution; D003643:Death; D004777:Environment; D006801:Humans; D008136:Longevity / Q000502:physiology*; D015233:Models, Statistical