Population genetics of two rare perennials in isolated wetlands: Sagittaria isoetiformis and S. teres (Alismataceae)
Adrienne L. Edwards and Rebecca R. Sharitz
Department of Botany, University of Georgia, Athens, Georgia 30602 USA;
Abstract: We investigated genetic structure in two closely related perennial plants that occur in isolated wetlands: Sagittaria isoetiformis, restricted to the southeastern Coastal Plain of North America, and S. teres, endemic to the northeastern Coastal Plain. Using horizontal starch-gel electrophoresis, we screened 527 individuals from 11 populations of S. isoetiormis and 367 individuals from seven populations of S. teres. A high proportion of the 16 loci were polymorphic (%PS = 93.8% in S. isoetiformis and (%PS = 75.0% in S. teres), with higher mean numbers of alleles per polymorphic locus and effective alleles per locus in S. isoetiformis (AP = 3.27, AE = 1.90) than in S. teres (AP = 2.58, AE = 1.30). Species- and population-level expected heterozygosities were higher in S. isoetiformis (HES = 0.399, HEP = 0.218) than in S. teres (HES = 0.177, HEP = 0.101). Jackknife estimates of F statistics indicated moderate levels of inbreeding in S. teres (FIS = 23.1%). Strong differentiation characterized these geographically isolated populations (GST = 39.9% S. isoetiformis, and GST = 26.1% in S. teres. Genetic identities varied substantially within (I = 75%, range = 0.558-0.963 in S. isoetiformis; I = 89%, range = 0.776-0.963 in S. teres) and among species (I = 81%, range = 0.506-0.882), leading to the discrimination of four regional population clusters using nonmetric multidimensional scaling (NMDS). It appears that S. isoetiformis and S. teres are a progenitor-derivative species pair.
Keywords: Alismataceae; allozymes; habitat isolation; progenitor-derivative; Sagittaria isoetiformis; Sagittaria teres
SREL Reprint #2469
Edwards, A.L., and R.R. Sharitz. 2000. Population genetics of two rare perennials in isolated wetlands: Sagittaria isoetiformis and S. teres (Alismataceae). American Journal of Botany 87:1147-1158.