Homoploid Hybridization and Its Role in Emergence and Diversity of the Genus Origanum L. (Lamiaceae)

Abstract

Hybrid specimens can be occurred as same ploidy level (homoploidy) or not (polyploidy) with its parents. Homoploid hybrids are originated without any change in their ploidy level (2n) and polyploid hybrids are produced with the change in ploidy level (3n, 4n etc.). According to recent studies, the frequency of natural hybridization (homoploid and polyploid) has been estimated to 25% of all flowering plants. Recent studies show that the genus Origanum has homoploid hybrids. Hybridization is a common phenomenon among the species of Origanum in overlapping distribution habitats (natural or cultivated areas). Ietswaart suggested that the hybridization process is a significant factor in the speciation of Origanum, and Origanum is probably caused by the hybridization of the old tribe Saturejeae (now tribe Mentheae) genera. Based on the hypothesis of Ietswaart, we can discuss the emergence of the genus Origanum, its intrageneric speciation and its hybrids having the possibility for speciation via hybridization using morphological and cytological evidence. During the field studies, it was seen that many populations of wide-distributed species were overlapping, and some Origanum putative hybrid specimens were also observed in these overlapping areas with morphological differences from their parents. All studied Origanum species and hybrids have 2n = 30 chromosome numbers to define homoploidy. Palynological characters were revealed, and intermediate pollen structure (size, P/E ratio etc.) was seen in the hybrids between their parents. In addition, DNA extractions were done from all the hybrids and their parents. nrITS DNA was sequenced. Hybrid specimens have some heterozygous DNA loci in comparison to their parents. This study presents some evidence about homoploid the hybridization of the genus Origanum put forward by Ietswaart. If habitat, ecological and geographic isolations occur between the hybrids and their parents, these hybrids can be speciation via homoploid hybridization in the future.