Genetic diversity and population structure of the mistletoe Tristerix corymbosus (Loranthaceae)

The genetic structure of a plant species is influenced by life-history traits, geographical range and ecological interactions that shape gene flow. We examined the genetic structure of the South American mistletoe Tristerix corymbosus using random amplification of polymorphic DNA. This species is found mainly in Chile and inhabits two biomes, the Chilean matorral and the temperate forest. The main pollinator agent, a hummingbird, is the same across the whole range, but the disperser assemblage varies between biomes. We selected 22 populations, eight of which were located in the Chilean matorral, where fruits are yellow and birds act as seed dispersers, and 14 populations in the temperate forest, where fruits are green and a marsupial disperses the mistletoe seeds. A total of ten primers were used to generate amplification products for 121 individuals (ca. six individuals per population) and 91 bands were scored. Results show that this mistletoe species is highly variable with 81 % of the bands polymorphic and a Shannon's diversity index among populations of 0.634. The temperate forest shows slightly higher diversity indices than the Chilean matorral. The central region of the mistletoe geographic range was more variable than the north and the south regions, suggesting that it is a genetically mixed zone. It is likely that gene flow occurs mainly via hummingbirds moving pollen between biomes and birds moving seeds from north to south during spring migrations.