Unravelling allopolyploid origins in the Alyssum montanum-A. repens species complex (Brassicaceae): low-copy nuclear gene data complement plastid DNA sequences and AFLPs
Abstract
Reconstructing polyploid origins and reticulate evolution is challenging even if several independent markers are employed. The Alyssum montanum-A. repens group is a species complex comprising multiple polyploids with as yet insufficiently investigated origins.
Here we search for the parentage of two related polyploids, A. montanum (s.s.) and A. rhodanense, using sequences of two low-copy nuclear genes and show how these data can complement and strengthen evidence based on plastid DNA and AFLPs. Whereas A. montanum, even in its strict circumscription, represents a complex of diploid and tetraploid lineages distributed from south-western Germany and western Switzerland to the foothills of the Pyrenees, A. rhodanense is a hexaploid stenoendemic from south-eastern France.
In both polyploids, we revealed divergent gene copies (homoeologues) that point to their allopolyploid origins and allow the identification of their parental species. The results suggest that tetraploids of A. montanum originated from hybridization between diploids of this species and the Iberian A. fastigiatum and that multiple allopolyploidization events took place.
For A. rhodanense, we propose an allopolyploid origin involving A. gmelinii and tetraploids of A. montanum. We illustrate how combined evidence from several markers contributes to more comprehensive and confident inferences about polyploid origins.