Genetic Structure and Gene Flow among South Florida Populations ofIris hexagonaWalt. (Iridaceae) Assessed with 19 Microsatellite DNA Loci

Abstract

We investigated genetic variation within and among 11 populations of Iris hexagona at its southern limits in the Florida peninsula by using 19 microsatellite loci. All of the populations contain varying numbers of identical multilocus genotypes, indicative of clonal reproduction. Two population samples consist largely of one clonal lineage and two clonal lineages: the first from the Caloosahatchee drainage west of Lake Okeechobee and the other from the Big Cypress Swamp. The populations are predominantly outcrossing, with high levels of heterozygosity, and show a highly significant pattern of isolation by distance that fits a modified stepping‐stone model. This pattern breaks down at the local level, however, where metapopulation dynamics or asymmetrical gene flow may exert a stronger effect on patterns of genetic diversity. Though the majority of genetic variation is within populations, 20% occurs between populations. Genetic distance resolves five clusters: four in the Caloosahatchee Valley and one in the Big Cypress Swamp. However, the populations are differentiated strongly enough that frequency‐based genetic structure analysis resolves seven effective populations. Assignment tests identify the northernmost population as a likely ancestral point of origin for the others. All of the populations exhibit evidence of a recent bottleneck, which we attribute to founder effects, given the low migration rate of the species and the high degree of population differentiation, as well as the Holocene geological history of the Florida peninsula. We hypothesize that the two predominantly clonal populations may be artifacts of deliberate cultivation by humans.