The cost of germline maintenance and repair gives rise to a trade-off between immutability (lowering deleterious mutation rates) and life-history functions. Life-histories and the mutation rate therefore co-evolve, but this joint evolutionary process is not well understood. I present a mathematical model to analyse the long-term evolution of traits affecting life-histories and deleterious mutation rate. I show that evolutionary stable life-histories and mutation rates can be characterised using the basic reproductive number of the least-loaded class (expected lifetime production of offspring without deleterious mutations born to individuals with the smallest number of deleterious mutations). We further analyse two specific biological scenarios: (i) co-evolution between reproductive effort and mutation rate and (ii) co-evolution between age at maturity and mutation rate. These two scenarios suggest two results. First, the trade-off between immutability vs life-history functions depends strongly on environmental conditions and baseline mutation rate. For example, low external mortality and high radiation environment favour high investment into immutability. Second, the trade-offs between different life-history factors can be strongly affected by mutation rate co-evolution and higher baseline mutation rates select for “faster life histories”: (i) higher investment into fecundity at the expense of survival and (ii) earlier age of maturation at smaller sizes. I will also discuss the implications of this model on understanding evolution of ageing and I will give an overview of my future research agenda concerning the evolution of ageing.
