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 allot etraploid species, Paeonia peregrina and a member of the Paeonia arietina s pecies group. Three phylogenetically distinct types of Adh sequences have b een identified from both accessions of P. officinalis, of which two types a re 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 last fro m the hybrid genome, possibly through backcrossing with the P. arietina gro up. This is a documentation of homoploid hybrid speciation between allotetr aploid species in nature. This study suggests that hybrid speciation betwee n allotetraploids can occur without an intermediate stage of genome diploid ization or a further doubling of genome size.