No evidence of contemporary interploidy gene flow between the closely related European woodland violets Viola reichenbachiana and V. riviniana (sect. Viola, Violaceae)

Abstract

Viola reichenbachiana (2n = 4x = 20) and V. riviniana (2n = 8x = 40) are closely related species widely distributed in Europe, often sharing the same habitat throughout their overlapping ranges. It has been suggested in numerous studies that their high intraspecific morphological variability and plasticity might have been further increased by interspecific hybridisation in contact zones, given the sympatry of the species and the incomplete sterility of their hybrid. The aims of this study were to: (i) confirm that V. reichenbachiana and V. riviniana have one 4x genome in common, and (ii) determine the impact of hybridisation and introgression on genetic variation of these two species in selected European populations. For our study, we used 31 Viola populations from four European countries, which were analysed using AFLP and sequencing of a variable plastid intergenic spacer, trnH-psbA. Our analysis revealed that V. reichenbachiana exhibited larger haplotype diversity, having three species-specific haplotypes versus one in V. riviniana. The relationships among haplotypes suggest transfer of common haplotypes into V. riviniana from both V. reichenbachiana and hypothetically the other, now extinct, parental species. AFLP analysis showed low overall genetic diversity of both species, with V. riviniana showing higher among-population diversity. None of the morphologically designated hybrid populations had additive AFLP polymorphisms that would have indicated recent hybridisation. Also, kinship coefficients between both species did not indicate gene flow. V. riviniana showed significant population subdivision and significant isolation by distance, in contrast to V. reichenbachiana. The results indicate lack of gene flow between species, high influence of selfing on genetic variability, as well as probably only localised introgression toward V. riviniana.

Complex Scenarios of Reticulation, Polyploidization, and Species Diversity within Annual Pansies of Subsect. Bracteolatae (Viola Sect. Melanium, Violaceae) in Italy: Insights from 5S-IGS High-Throughput Sequencing and Plastid DNA Variation

“…Many studies have been carried out to address phylogenetic and taxonomic questions at the infrageneric level in Viola, e.g., [ 1 , 40 , 43 , 56 ]. Our study is the first to report data from extensive intra- and interspecific investigations on a specific group within sect.…”

“…In addition, the use of multi-locus ribosomal DNA in polyploid and hybridogeneous taxa may be problematic due to the frequent occurrence of paralogous sequences and complex mechanisms leading to intra- and interlocus sequence evolution and homogenization [ 42 ]. Species-level molecular diversity is even harder to assess: ISSR and AFLP can provide interesting results in species delimitations [ 4 , 39 ], but phylogenetic inferences are made complicated by frequent hybridizations, the assumed reticulate evolution, and ploidal variability among the different species, but see [ 43 ].…”

Seasonal and Simultaneous Cleistogamy in Rostrate Violets (Viola, subsect. Rostratae, Violaceae)

“…Our results documented constant differences between CH and CL flowers at different stages of their development and at fruiting, allowing for the easy recognition of fruits derived from CH or CL flowers. CH flowers attract insect pollinators and promote cross-pollination and potential genetic diversity within populations [ 34 , 35 , 36 , 37 , 38 , 39 , 40 ]. In contrast, obligate self-pollinated CL flowers produce pure lines.…”

Interspecific Hybridization and Introgression Influence Biodiversity—Based on Genetic Diversity of Central European Viola epipsila-V. palustris Complex

“…Bootstrap for NeighborNet was calculated on 2000 replicates. Identification of admixture and inference of population structure was done using clustering method on unlinked dominant markers [34] in STRUCTURE v. 2.3.4 [35], which has been widely used for inference of population structure in polyploids using dominant markers [36][37][38][39][40] also for species of the genus Viola [41,42]. STRUCTURE analysis, implemented in R v. 3.6.3 package ParallelStructure [43], assumed admixture between populations, and correlated allele frequencies between clusters.…”