High genetic variation and low gene flow among populations of Viscum verrucosum in semi-arid savanna, southwest Zimbabwe

Despite the increasing recognition of the ecological role of mistletoes, little is known about their genetic diversity. In this regard, we assessed the genetic variation within and among populations of Viscum verrucosum using random amplified polymorphic DNA (RAPDs). Analysis of molecular variance (AMOVA) and phylogenetic analysis based on genetic distance matrices were used to partition variation within and among populations, and the relationship between geographical and genetic distance was established using a Mantel's test. Mean population genetic diversity was high (P = 77.19%, A = 1.58, h = 0.30, Hʹ = 0.44) relative to other outcrossing mistletoe species. Genetic differentiation among the populations was high (GST = 0.366), also with low gene flow (Nm = 0.433) among populations. The genetic distance was significantly correlated to geographic distance (r = −0.849, p = 0.002), consistent with isolation-by-distance model suggesting constrained genetic exchange between geographically distant populations. Consequently, most of the genetic variation was retained within (63%) than among (37%) populations. In conclusion, findings of this study suggest that isolation-by-distance coupled with low seed dispersal limit gene flow, and determine the high levels of genetic structure of V. verrucosum populations, while historically elevated rates of gene flow may explain the high genetic diversity detected in these populations.