SENESCENCE IN ORGANISMS WITH CLONAL REPRODUCTION AND COMPLEX LIFE-HISTORIES

A population genetics model is developed predicting the fate of allele s affecting life-history attributes in organisms with complex life his tories, including clonal reproduction and indeterminate growth. Such o rganisms are widespread and found in many ecologically important group s, including marine invertebrates such as corals and sponges, and most higher plant taxa. The evolution of senescence (here defined as a dec rease in fitness components with age or stage) by the action of allele s having negatively pleiotropic stage effects is investigated in such organisms. The spread of these alleles depends on the sensitivity of t he population growth rate, a measure of fitness, to changes in life-hi story parameters that for this model are the entries of the stage tran sition matrix. Examples from a published demographic study show that, for several cases examined, alleles increasing early survival or early reproduction at the cost of decreased late survival will not be favor ed. Clonal reproduction acts to retard the evolution of senescence, al though by itself the existence of clonal reproduction in an organism d oes not preclude the evolution of senescence.