Evolutionary History of Paysonia (Brassicaceae)

Abstract

Paysonia is a small genus of annuals consisting of eight species; three are found in Texas and Oklahoma and the remaining five are in the Central Basin of Tennessee and northern Alabama. Species are morphologically distinct, but interspecific relationships are uncertain. To investigate evolutionary relationships in a phylogenetic context, the internal transcribed spacer (ITS) region of nuclear ribosomal DNA and three chloroplast markers were sequenced for multiple accessions from different populations of each species. Although little phylogenetic resolution was found among the Tennessee/Alabama species, each of the Texas/Oklahoma species is monophyletic. These phylogenetic analyses suggest that both incomplete lineage sorting and gene flow may be complicating the recovery of evolutionary relationships among the southeastern species. To test for evidence of present day hybridization in Tennessee, multiple microsatellite markers were used to document gene flow among populations of each species. Results indicate a complex combination of relationships and present day gene flow in these species; the data in combination suggest that each species is a separately evolving metapopulation lineage.