SIGNIFICANT POTENTIAL LEVELS OF HIERARCHICAL PHENOTYPIC SELECTION IN A WOODY PERENNIAL PLANT, CISTUS-LADANIFER

Cistus ladanifer L. is a Mediterranean woody perennial species (with two varieties: var. albiflorus and var. maculatus) that follows an obligatory seeder strategy for post-fire seedling establishment. Large numbers of seeds are produced inside fruit capsules split up into compartments. The capsules are the result of apical meristems and appear in different shoot modules and branches throughout the plant. Seed production, used here as a measure of fitness, can thus be analyzed hierarchically in the different structural levels of the plant. A nested analysis of variance was used to test the heterogeneity in the reproductive output of this species in the hierarchical structural arrangement of the individual plants, in order to provide empirical evidence on the potential of hierarchical phenotypic selection, a theoretical framework recently developed for the evolutive processes in modular organisms. With the exception of the only supra-individual level tested (subpopulations of varieties), all levels (shoot modules, branches, and genetic individuals) were significantly heterogeneous in the seed production. The heterogeneity of each level is independent of that of the other levels. In the same way as the heterogeneity in selective traits of genetic individuals is a usual prerequisite for classical selection in unitary organisms, an equivalent heterogeneity should be demonstrated in the different levels of modular organisms for the possible action of phenotypic hierarchical selection upon those levels. The analysis method used here is considered as a valid procedure for the detection of significant potential levels of hierarchical phenotypic selection in modular organisms.