Allotetraploid Speciation And Evolution

Questions about speciation is the"mystery of mysteries"in Evolutionary Biology. It is especially difficult to understand where adaptive radiation occurs. Hybridization and polyploidy often create new adaptive traits or trait combination through genome reshuffling and duplication, and through altering gene expression patterns, and thus promote speciation. This research studies the North Hemisphere genus Achillea L. (Asteraceae). With DNA sequences data of nuclear single-copy genes and plastid non-coding regions, we are able to untangling the process of the allopolyploids formation, persistence and phylogeography of two Eastern Asian allopolyploid species Achillea alpina-4x and A. wilsoniana-4x of the genus Achillea. Available data suggest that the two tetraploid species arose by hybridization followed by polyploidy. In the gene trees, sequences of the 4x accessions do not form any species specific clades while both the diploid parental species do. The two tetraploid species are derivatives of a 4x ancestor arisen from hybridization between an A. acuminata-like and an A. asiatica-like parent. The cpDNA sequence data further demonstrate that the maternal dornor is of the A. asiatica-lineage, and the paternal dornor of the A. auminata-lineage. Furthermore, we find evidence for interploidy backcrossing gene flow between one of the parental and one of the tetraploid derivative species.Polyploidy is a common phenomenon in flowering plants. A growing body of evidence indicates that polyploidy evolution is an ongoing, dynamic process in plant speciation. Many taxonomically recognized polyplods have originated multiple times. Altogether, the findings from this study clearly demonstrate allopolyploid speciation and ongoing backcrossing between the parental and daughter taxa. Such evolutionary processes may explain the great diversity in many polyploid species complexes and illustrate their importance for evolutionary radiation in angiosperms.