Population Structure and Local Differentiation in Liatris cylindracea

Abstract

An analysis of genetic population structure and local differentiation was conducted in the obligatory outbreeding prairie herb Liatris cylindracea. A single population located along an environmental gradient on a hillside in Zion, Lake County, Illinois, was divided into 60 3-m2 quadrats, the quadrat size approximating the neighborhood size of Liatris. Gene frequencies of 15 polymorphic and 12 monomorphic allozyme loci were determined on a per quadrat basis. The population exhibited marked local genetic differentiation; gene frequencies sometimes varied as much as 20% between adjacent quadrats. Correlation of gene frequency with edaphic factors at the site proved non-significant at 13 loci and negatively correlated at two loci, Est3 and Per-. Population structure was analyzed by both χ2 and F statistics. Both FIS, the within-subdivision deviation from Hardy-Weinberg equilibrium frequencies, and FST, the degree of population substructuring, are significant, with FIS values ranging from 0.1 to 0.506 and FST ranging from 0.009 to 0.224. The genetic substructuring of the L. cylindracea population is attributed to restricted gene flow, and the role of pollinator behavior and seed dispersal in population substructuring is discussed.