Genetic differentiation of Microseris pygmaea (Asteraceae, Lactuceae) studied with DNA amplification from arbitrary primers (RAPDs)

The diploid annual Microseris pygmaea is the only Chilean species of the genus and is closely related to M. bigelovii and M. elegans of California. It must have reached Chile by long-distance dispersal from California and have gone through a single-plant bottleneck before becoming established. Previous data on iso-enzyme alleles and morphology have separated coastal from inland populations and suggested that range expansion took place by stepwise founder effects creating a set of nested monophyletic groups of populations. Here, we test this hypothesis on 10 strains from nine representative populations using nuclear DNA fragments amplified in vitro from short arbitrary primers (RAPDs) as characters. We obtained 208 amplification products with 24 primers. Of these, 91 were shared by all strains, 93 were informative. The data confirm that coastal and inland populations form two distinct monophyletic groups, but show relatively weak differentiation within each of these groups indicating some gene flow and recombination among neighbouring populations. Homoplasy in the data due to all possible sources including faults in band interpretation is estimated at about 10%. A cladogram of the two genetically most divergent strains of M. pygmaea, M. bigelovii and M. elegans shows that each species is monophyletic but does not suggest any closer association between M. pygmaea and one of its possible ancestral species.