Fitness and evolution in clonal plants: the impact of clonal growth

Abstract

Seeds have often been emphasized in estimates of plant fitness because they are the units that carry genes to the next generation, disperse, and found new populations. We contend that clonal growth also needs to be considered when estimating fitness in clonal plants, regardless of whether fitness is measured from a genet or ramet perspective. Clonal growth affects genet fitness through both genet persistence and seed production. It affects ramet fitness through new ramet production, because both seeds and clonal propagants are considered offspring. The differential production of clonal propagants will contribute to fitness differences among individuals which may result in population-level changes in allele frequencies (i.e. microevolution). We describe a form of selection unique to clonal organisms, genotypic selection, that can result in evolution. Genotypic selection occurs when genotypically based traits are associated with differences in the rate of ramet production. It can lead to evolutionary change in quantitative trait means both directly and indirectly. It leads directly to change in the ramet population by increasing the proportion of ramets with more advantageous trait values. From the genet perspective, it leads indirectly to evolution within and among populations whenever significant portions of the genetic effect on a trait are inherited through seed. We argue that under most conditions, clonal growth will play a major role in the microevolution of clonal plants.