@ARTICLE{TreeBASE2Ref17540, author = {Jenny E. E. Smedmark and Torsten Eriksson and Rodger C. Evans and Christopher S. Campbell}, title = {Ancient Allopolyploid Speciation in Geinae (Rosaceae): Evidence from Nuclear granule-Bound Starch Synthase (GBSSI) Gene Sequences.}, year = {2003}, keywords = {}, doi = {10.1080/10635150390197000}, url = {}, pmid = {}, journal = {Systematic Biology}, volume = {52}, number = {3}, pages = {374--385}, abstract = {A nuclear low copy gene phylogeny provides strong evidence for the hybrid origin of seven polyploid species in Geinae. In a gene tree, alleles at homoeologous loci in an allopolyploid species are expected to be sister to orthologues in its ancestral taxa rather than to each other. Alleles at a duplicated locus in an autopolyploid, on the other hand, are expected to be more closely related to each other than they are to any orthologous copies in closely related species. We cloned and sequenced about 1.9 kb from the 5' end of the GBSSI-1 gene from two diploid, one tetraploid and six hexaploid species. Each of the three loci in the hexaploid species forms a separate group of which two are more closely related to copies in other species than they are to each other. This indicates that the hexaploid lineage evolved through two consecutive allopolyploidisation events. Based on the GBSSI-1 gene tree we hypothesise an initial hybridisation between a diploid from the ancestral lineage of Coluria and Waldsteinia and an unknown diploid species, to form the tetraploid Geum heterocarpum lineage. Backcrossing of G. heterocarpum with a representative of the unknown diploid lineage, is suggested to have resulted in a hexaploid lineage that has radiated considerably since its origin, comprising at least 40 extant species with varying morphology. A Penalized likelihood analysis indicates that Geinae may be about 17 million years old, implying that the hypothesised allopolyploid speciation events are relatively ancient. Six of the 22 cloned Geinae GBSSI-1 copies in this study, which all are duplicate copies in polyploid taxa, may have become pseudogenes. The GBSSI-1 phylogeny is compared with one from chloroplast data, and implications for the evolution of some fruit characters are discussed.} }

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