Reciprocal hybridization between diploid Ficaria calthifolia and tetraploid Ficaria verna subsp. verna: evidence from experimental crossing, genome size and molecular markers

Abstract

Ficaria is a taxonomically intriguing polyploid complex with high morphological variability. Both hybridization and polyploidization have been suggested as the main evolutionary forces behind the high morphological variability in this genus; however, detailed studies are lacking. In Central Europe, two Ficaria taxa (diploid F. calthifolia and tetraploid F. verna subsp. verna) occasionally co-occur in local sympatry, which might result in hybridization. We investigated sympatric populations of the two Ficaria taxa using flow cytometry, chromosome counts, AFLP analysis and plastid DNA sequencing; we also performed experimental homoploid and heteroploid crosses to determine the frequency and direction of hybrid triploid formation, an alternative route of triploid origin (autopolyploidy) and the possibility of a one-step neoallotetraploid origin. Sympatric populations were composed of three genetic clusters corresponding to diploid F. calthifolia (2n = 16), tetraploid F. verna subsp. verna (2n = 32) and triploid plants (2n = 24). The holoploid genome size and AFLP data suggest a hybrid origin of the triploids, thereby making their formation via autopolyploidization in F. calthifolia unlikely. The triploid populations are monoclonal and of independent origin. In contrast, the parental populations exhibit high genotypic diversity and frequent sexual reproduction, including those of predominantly asexual F. verna subsp. verna. Experimental crossing confirmed that both parental taxa produce fertile seeds via a sexual pathway, but not by apomixis, and that both serve as pollen acceptors in heteroploid crosses, which is consistent with the plastid sequencing. However, hybridization is asymmetric, with maternal-excess crosses being significantly more successful. No signs of neoautotetraploidization or neoallotetraploidization were detected. In summary, recent gene flow between the studied Ficaria taxa is either limited or absent.

Mahonia vs. Berberis Unloaded: Generic Delimitation and Infrafamilial Classification of Berberidaceae Based on Plastid Phylogenomics

“…Under this scenario, Berberis and Mahonia should be the maternal parents for Moranothamnus and Alloberberis (Figure 3), respectively, given cytoplasmic DNA is known to be maternally inherited in Berberidaceae (Zhang et al, 2003). Coupled with the ancient splits of the four genera (Figure 5), Alloberberis and Moranothamnus could have resulted from ancient reciprocal hybridization (Popelka et al, 2019) between Berberis and Mahonia preceding subsequent radiations of the two parental genera (García et al, 2017). Additionally, the hybrid origins of Alloberberis and Moranothamnus could also explain their combined morphology and more restricted geographic distributions relative to Berberis and Mahonia (Yu and Chung, 2017).…”

Disentangling the components of triploid block and its fitness consequences in natural diploid–tetraploid contact zones of Arabidopsis arenosa

“…A similar, relatively weaker, barrier in the maternal excess crosses was found in other mixed‐ploidy systems covering Angiosperm diversity (e.g. Koutecký et al., 2012; Kopecký et al., 2018; Popelka et al., 2019), although it has been only rarely linked with investigation of endosperm phenotype (Scott et al., 1998; Stoute et al., 2012; Sekine et al., 2013). Interestingly, the opposite direction of asymmetry was observed in some Mimulus species (Vallejo‐Marín et al., 2016; Meeus et al., 2020).…”

Genetic and Morphological Comparisons of Lesser Celandine (Ficaria Verna) Invasions Suggest Regionally Widespread Clonal and Sexual Reproduction

“…Other studies have estimated genetic and morphological diversity of European celandine populations, and these serve as a basis for comparing diversity in the introduced range. Our population estimates of Nei's genetic diversity ranged from 0.251 to 0.406, while those estimated in Europe have varied widely: 0.05-0.22 using RAPD (Reisch and Scheitler 2008) and 0.41-1.00 using AFLP (Popelka et al 2019), meaning that some introduced populations may be more genetically diverse than native populations (assuming diversity estimates were not biased by sampling artifacts). Previous work synthesizing comparisons of genetic diversity among introduced and native populations similarly showed wide variation in outcomes, with a trend towards higher genetic diversity in cases of multiple introductions (Dlugosch and Parker 2008).…”

“…Furthermore, we do not know if apomixis occurred or whether the expanded achenes had no embryo inside, both of which have been previously documented in bulbiferous celandine (Metcalfe 1939). Still, more recent work has shown that bulbiferous tetraploids (speci cally verna) can produce fertile seeds (Popelka et al 2019), through either cross pollination or self-pollination (Marsden-Jones and Turrill 1952). Despite these caveats, the potential that ripened achenes were produced raises the possibility that sexual reproduction is possible for introduced celandine populations.…”