Polyploidy, hybridization and evolution in Pratia (Campanulaceae)

Evolution in the genus Pratia (Campanulaceae) has been studied using a variety of techniques. The distribution of chromosome races in P. angulata has been plotted and results suggest that although they generally occupy different geographic areas there are large areas of overlap. No consistent morphological differences were found between these chromosome races. The existence of hybrids between P. angulata and P. perpusilla with 11x and 13x chromosome numbers has been established using genomic in situ hybridization (GISH), and random amplified polymorphic DNA (RAPD) analysis suggests several independent origins for these hybrids. Artificial hybridization studies showed a high degree of compatibility in almost all the combinations that were attempted. DNA sequences derived from both the nuclear genome (internal transcribed spacer of the rDNA locus, ITS) and chloroplast genomes (trnL intron and trnL-trnF spacer) were used to construct phylogenies. Colensoa physaloides has been shown to be distinct from the New Zealand species of Pratia and was used as an outgroup to root the phylogenetic trees. A significant finding is that P. macrodon is sister to the other New Zealand species. DNA sequence data also confirm the hybrid origin of the 11x and 13x plants and show that P. perpusilla is the maternal parent of the 11x plants and P. angulata is the maternal parent of the 13x ones. The origin of the putative hybrid plants with the 12x chromosome number remains to be elucidated.