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

Abstract

The Viola epipsila-V. palustris complex is a highly taxonomically complicated group of species in its entire circumboreal range of distribution. Habitat loss, forest flooding, and hybridization could lead to the extinction of V. epipsila. A hybrid index and principal component analysis (PCA) were used to select qualitative and quantitative morphological features to distinguish parent species and hybrids, inter simple sequence repeat (ISSR) markers to determine the genetic diversity of the populations, flow cytometry to estimate the genome size (GS), and non-coding chloroplast DNA (cpDNA) regions to indicate the directions of crosses. All taxa are very morphologically variable, and their features can change within a season. The most stable feature is the distance of the bracts on the pedicel from the rhizome. The genetic diversity of all taxa populations is low and highly influenced by selfing and vegetative propagation. The population structure is differentiated: populations of V. epipsila or V. palustris, mixed populations with both parent species, F1 hybrids and populations with introgressive forms occur in different regions. The interspecific GS variation corresponds to the ploidy level (4x = 2.52 pg, 8x = 4.26 pg, 6x = 3.42 pg). Viola epipsila is the mother plant of the hybrids. Research has shown the risk of V. epipsila extinction in Central Europe and the importance of local populations in studying the role of hybridization in reducing/maintaining/increasing biodiversity.

Detecting Introgressed Populations in the Iberian Endemic Centaurea podospermifolia through Genome Size

“…Overall, in order to contribute further to the conservation and monitoring of these species, future population genetics surveys would be desirable to tackle, as well as the potential taxonomic questions arising from the apparent recurrent introgression in Ports Massif. The use of high throughput approaches (e.g., RADseq [ 13 , 20 ]) has been crucial to untangle the complex backgrounds of hybridisation in plants. Such techniques combined with flow cytometry would certainly enable reaching more sound conclusions about the genetic background of Centaurea in this area, including the level of introgression within and between populations.…”

“…Besides the use of genetic markers to uncover the genetic signature of crosses between species, flow cytometry has been widely used at population level to detect changes in nuclear DNA contents, i.e., intraspecific and cytotype variation, which is frequently one of the outcomes of hybridisation (e.g., Sorbus, Viola [ 9 , 13 , 14 ]). Indeed, this technique has become a complementary tool to interpret output data from population genetics (i.e., allelic frequencies).…”

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.…”

Genetic Variation versus Morphological Variability in European Peatland Violets (Viola epipsila—V. palustris Group)

“…Viola epipsila and V. palustris both occur in wetlands, although V. epipsila prefers rather eutrophic groundwater-influenced fen habitats and is associated with wet alder stands; V. palustris , with a wider ecological tolerance, occurs in peatland vegetation, in wet meadows, and in pastures [ 10 , 17 , 29 , 30 ]. The overlapping ranges and flowering of chasmogamous (CH) flowers of these closely related allopolyploids, which share a genome, weakens the isolation barriers, creating suitable conditions for interspecific hybridization, and leading to the genetic diversity of the complex [ 1 , 9 , 10 , 11 , 30 ]. The wetland areas have drastically decreased because of the combined effect of climate change and drainage.…”

“…The wetland areas have drastically decreased because of the combined effect of climate change and drainage. As a consequence, the habitats of both species are disappearing and their ranges, especially that of V. epipsila , are declining in Central Europe [ 30 ]. These species may be considered as indicators of the state of the peatlands they occupy; the decreasing numbers of individuals or the disappearance of whole subpopulations of both species indicate a large-scale change in the wetland and peatland habitats.…”