Speciation through homoploid hybridization between allotetraploids in peonies (Paeonia)

Phylogenies of Adh1 and Adh2 genes suggest that a widespread Mediterranean peony, Paeonia officinalis, is a homoploid hybrid species between two allotetraploid species, Paeonia peregrina and a member of the Paeonia arietina species group. Three phylogenetically distinct types of Adh sequences have been identified from both accessions of P. officinalis, of which two types are most closely related to the two homoeologous Adh loci of the P. arietina group and the remaining type came from one of the two Adh homoeologs of P. peregrina. The other Adh homoeolog of P. peregrina was apparently lost from the hybrid genome, possibly through backcrossing with the P. arietina group. This is a documentation of homoploid hybrid speciation between allotetraploid species in nature. This study suggests that hybrid speciation between allotetraploids can occur without an intermediate stage of genome diploidization or a further doubling of genome size.