Genetic Variability in Balkan Paleoendemic Resurrection Plants Ramonda serbica and R. nathaliae Across Their Range and in the Zone of Sympatry

Abstract

The genus Ramonda includes three Paleoendemic and Tertiary relict species that survived in refugial habitats of the Balkan Peninsula (R. nathaliae and R. serbica) and the Iberian Peninsula (R. myconi). They are all “resurrection plants,” a rare phenomenon among flowering plants in Europe. Ramonda myconi and R. nathaliae are diploids (2n = 2x = 48), while R. serbica is a hexaploid (2n = 6x = 144). The two Balkan species occur in sympatry in only two localities in eastern Serbia, where tetraploid potential hybrids (2n = 4x = 96) were found. This observation raised questions about the existence of gene flow between the two species and, more generally, about the evolutionary processes shaping their genetic diversity. To address this question, genetic markers (AFLP) and an estimate of genome size variation were used in a much larger sample and at a larger geographic scale than previously. The combination of AFLP markers and genome size results suggested ongoing processes of interspecific and interploidy hybridization in the two sites of sympatry. The data also showed that interspecific gene flow was strictly confined to sympatry. Elsewhere, both Ramonda species were characterized by low genetic diversity within populations and high population differentiation. This is consistent with the fact that the two species are highly fragmented into small and isolated populations, likely a consequence of their postglacial history. Within sympatry, enormous variability in cytotypes was observed, exceeding most reported cases of mixed ploidy in complex plant species (from 2x to >8x). The AFLP profiles of non-canonical ploidy levels indicated a diversity of origin pathways and that backcrosses probably occur between tetraploid interspecific hybrids and parental species. The question arises whether this diversity of cytotypes corresponds to a transient situation. If not, the question arises as to the genetic and ecological mechanisms that allow this diversity to be maintained over time.

Asymmetric Introgression and Cryptic Natural Hybridization between Two Species of Teucrium Section Polium (Lamiaceae) on the Balkan Peninsula

“…Backcrossing with one or both parental species can result in individuals that are morphologically difficult to distinguish from the parent species, making the identification of hybrids based on morphology challenging or impossible. This phenomenon has already been observed in numerous plant genera, including Cardamine [ 39 ], Betula [ 35 ], Pinus [ 32 , 34 ], Knautia [ 40 ], Primula [ 41 ], Ruppia [ 42 ], Ramonda [ 43 ], etc.…”

Allopolyploidy: An Underestimated Driver in Juniperus Evolution

“…However, as noted by these authors, this should not inhibit the detection of hybridizations. Numerous studies have confirmed the power of AFLP markers in detecting interspecific hybridization (e.g., [23,24,[37][38][39]). Altogether, the 1022 loci produced in this study allowed a powerful discrimination between the studied species and the identification of several individuals that could be considered as progenies of interspecific hybridization.…”

Genome Size Variation in Sesamum indicum L. Germplasm from Niger

“…The variation in the GS among species is widely documented, particularly in plants [ 30 ], and its impacts play a key role in plant biodiversity, ecology and evolution [ 30 , 39 , 52 , 53 , 54 , 55 , 56 ]. There are also several reports on the relationship between the intraspecific variation in the GS and the phenotypic, phenological or ecological factors [ 28 , 31 , 34 , 57 , 58 , 59 , 60 ].…”