Chloroplast DNA evidence for the evolution of Microseris (Asteraceae) in Australia and New Zealand after long-distance dispersal from Western North America

Restriction site mutations and trnL(UAA)-trnF(GAA) intergenic spacer length Variants in the chloroplast genome were used to investigate the phylogenet ic relationships among 53 Australian and New Zealand Microseris populations and to assess their position within their primarily North American genus. The study was performed to enhance understanding of evolutionary processes within this unique example of intercontinental dispersal and subsequent ada ptive radiation. A southern blot method using four-base restriction enzymes and fragment separation on polyacryamide gels resulted in 55 mutations of which 30 were potentially phylogenetically informative. Most mutations were small indels of <162 bp, 80% of which were <20 bp. The small indels were u seful for phylogenetic reconstruction of Australasian Microseris as judged by the high consistency indexes. The results confirmed the monophyly of the Australian and New Zealand Microseris. The occurrence of "hard" basal poly tomies in the most parsimonious trees indicated that rapid radiation has oc curred early in the history of me taxon. The monophyly of M. lanceolata, wh ich includes the self-incompatible ecotypes of the Australian mainland, was confirmed. Within this species three clades were found that reflect more g eographic distribution than morphological entities, suggesting that migrati on and possibly introgression between different ecotypes. or parallel evolu tion of similar adaptations, has occurred. One of the three clades was supp orted by a 162-bp deletion in the trnL-trnF spacer, while a subgroup of thi s exhibited also a tandemly repeated trnF exon. The data were inconclusive about the monophyly of the second Australasian species, M. scapigera, which comprises the New Zealand, Tasmanian. and autofertile ecotypes of Australi a.