THE ORGANIZATION OF GENETIC VARIABILITY IN PHLOX DRUMMONDII.

Abstract

thousands of individuals. The species is divisible into six morphologically distinct subspecies which are largely allopatric or parapatric (Erbe and Turner, 1962). Their ranges are depicted in Figure 1. Subspecies glabriflora grows principally on stabilized sandy dune soils in open fields of the Coastal Plain, ssp-. littoralis on coastal beach sands, ssp. tharpii on sandy soils in open prairies of the Rio Grande Plain, ssp. goldsmithii and ssp. drummondii on sandy loams in open or cleared forest areas, and ssp. mcallisteri in open fields on shallow sandy soils of granitic origin on the Edwards Plateau. Reproductive barriers to gene exchange are weak (Erbe and Turner, 1962; Levin, 1976), and the integrity of the subspecies seems due to their ecogeographical isolation. All of the subspecies exhibit gametophytic self-incompatibility, and have the same chromosome number, n = 7. The primary objectives of this study are (1) to characterize each taxon in terms of gene frequencies, genetic diversity and genotype frequencies relative to HardyWeinberg expectation, (2) to apportion genetic diversity within and between subspecies, (3) to describe gene frequency heterogeneity between populations of the same subspecies and the species as a whole, (4) to describe geographical variation patterns for alleles and genetic diversity, and (5) to determine the genetic affinities of the subspecies. In doing this an attempt is made to discern the roles of gene flow restriction within and among populations and stochastic processes in fostering and maintaining the organization of genetic variability in P. drummondii. The concordance between morphological and allozymic variation also is considered. EVOLUTION 31:477-494. September 1977 477