Multiple origins and genetic diversity in the newly arisen allopolyploid species, cambrensis rosser (Compositae)

A survey of allozyme variation was conducted in populations of the newly arisen allopolyploid species Senecio cambrensis and its two parental species S. vulgaris and S. squalidus sampled from the three locations in Britain where S. cambrensis is known to occur, i.e. at Wrexham and Mochdre in Wales, and Edinburgh in Scotland. Electrophoretic variation at the Acp-1 and αEst-1 loci provided strong evidence of separate origins of S. cambrensis in Wales and Edinburgh. The possibility of two additional independent origins of the species in Wales was indicated by the variation pattern at the Aat-3 locus, although this variation could be explained as a result of segregation from a fixed heterozygote (representative of a single origin) following pairing between homoeologous chromosomes, as could the pattern of variation recorded at the βEst-3 locus. For no enzyme system were additional allozymes found in S. cambrensis which were not present in one of the respective parents. The ability of S. cambrensis to originate at different locations and to generate genetic diversity following recombination between its parental genomes, might act in favour of its establishment and diversification in Britain.