Cone and seed trait variation in whitebark pine (Pinus albicaulis; plnaceae) and the potential for phenotypic selection

Abstract

Phenotypic variation among individuals is necessary for natural selection to operate and is therefore essential for adaptive evolution. However, extensive variation within individuals can mask variation among individuals and weaken the potential for selection. Here we quantify variation among and within individuals in female cone and seed traits of whitebark pine (Pinus albicaulis). In many plants, the production of numerous reproductive structures creates the potential for considerable variation within a plant, but these same traits should also undergo strong selection because of their direct link to plant fitness. We found about twice as much variation among individuals (overall mean = 65.3 ± 4.5% SE) than within individuals (overall mean = 34.7 ± 4.5%). One only needs to sample three to five cones per tree to accurately assess variation among trees in most cone and seed traits. The ease at which trees can be assessed helps account for the strong and consistent patterns of phenotypic selection exerted by seed predators and dispersers of whitebark pine and many other conifers. In contrast, the few traits where variation within trees equaled or exceeded that among trees underwent weak if any phenotypic selection.