Local Differentiation for Phenotypic Plasticity in the Annual Collomia linearis (Polemoniaceae)

Abstract

A population of Collomia linearis was subdivided into two plots, one in a relatively disturbed site free from interspecific competition and the other in a meadow habitat characterized by high vegetative cover and considerable interspecific competition. Greenhouse progenies of the two subpopulations differed significantly with respect to seven morphological characters, indicating that the two subpopulations were genetically differentiated. Analysis of nine morphological characters in progenies subjected to 36 different environmental conditions revealed that plants of the disturbed plot were phenotypically more plastic than those of the meadow plot. It is concluded that phenotypic plasticity represents a genetic response and may arise through local differentiation under conditions of disruptive selection. Phenotypic plasticity represents the amount by which the genotypic expression of a character is changed by environmental conditions (Bradshaw, 1965; Davis & Heywood, 1963). Bradshaw reviewed evidence that demonstrates that plasticity is under genetic control and is alterable by selection. The potential for evolutionary differentiation between closely adjacent plant populations has been reviewed by Jain and Bradshaw (1966), Ehrlich and Raven (1969), and Bradshaw (1972) and has been empirically demonstrated by numerous studies (i.e., Bradshaw, 1959; Aston & Bradshaw, 1966; Snaydon, 1970; Linhart, 1974; Schaal, 1975). Such differentiation is often interpreted as adaptive with respect to the characters and divergent environments being compared. These studies lead to the hypothesis that phenotypic plasticity may result from disruptive selection within local plant populations. This paper presents evidence of local differentiation for phenotypic plasticity in Collomia linearis Nuttall (Polemoniaceae). Collomia linearis is an autogamous annual, occurs over a relatively broad range of habitats throughout western North America, and displays considerable phenotypic variation within and among natural populations (Grant, 1959; Grant & Grant, 1965; Hitchcock et al., 1959).