THE MERISTEM-MERISTEM CYCLE AS A BASIS FOR DEFINING FITNESS IN CLONAL PLANTS

In clonal plants the genetic individual may be exceedingly long-lived, and the traditional way of defining Darwinian fitness - i.e. on the basis of the zygote-zygote cycle - may therefore be impracticable. Yet, an obvious alternative, viz. to define fitness on the basis of the meristem-meristem cycle, has frequently been rejected. I suggest here that this rejection is unwarranted, and I present a quantitative measure of fitness in clonal plants that I consider to be of general applicability. Meristems are considered to have three developmental options: (i) to propagate vegetatively; (ii) to propagate sexually; (iii) to remain dormant. Each option leads to the perpetuation of the genome of a mother meristem from the time t1, to daughter meristems at the time t2; in the case of option (ii) a gene runs a risk of getting lost through meiosis. Fitness is defined as the rate of increase (over time, not generations) of a gene, the combination of options (i)-(iii) which maximizes this rate being most fit.