Genome Size as a Key to Evolutionary Complex Aquatic Plants: Polyploidy and Hybridization in Callitriche (Plantaginaceae)

Abstract

Despite their complex evolutionary histories, aquatic plants are highly underrepresented in contemporary biosystematic studies. Of them, the genus Callitriche is particularly interesting because of such evolutionary features as wide variation in chromosome numbers and pollination systems. However, taxonomic difficulties have prevented broader investigation of this genus. In this study we applied flow cytometry to Callitriche for the first time in order to gain an insight into evolutionary processes and genome size differentiation in the genus. Flow cytometry complemented by confirmation of chromosome counts was applied to an extensive dataset of 1077 Callitriche individuals from 495 localities in 11 European countries and the USA. Genome size was determined for 12 taxa. The results suggest that many important processes have interacted in the evolution of the genus, including polyploidization and hybridization. Incongruence between genome size and ploidy level, intraspecific variation in genome size, formation of autotriploid and hybridization between species with different pollination systems were also detected. Hybridization takes place particularly in the diploid – tetraploid complex C. cophocarpa – C. platycarpa, for which the triploid hybrids were frequently recorded in the area of co-occurrence of its parents. A hitherto unknown hybrid (probably C. hamulata × C. cophocarpa) with a unique chromosome number was discovered in the Czech Republic. However, hybridization occurs very rarely among most of the studied species. The main ecological preferences were also compared among the taxa collected. Although Callitriche taxa often grow in mixed populations, the ecological preferences of individual species are distinctly different in some cases. Anyway, flow cytometry is a very efficient method for taxonomic delimitation, determination and investigation of Callitriche species, and is even able to distinguish homoploid taxa and identify introduced species.

Is genome downsizing associated with diversification in polyploid lineages ofVeronica?

“…Previously, most genome size estimates had been generated using Feulgen densitometry (> 90% in Albach & Greilhuber, ), whereas now more than 70% of all estimates are from flow cytometry using both fresh and silica gel‐preserved material (see below for a discussion of methodological comparisons). In general, the range of genome sizes for Veronica fits in the lower half of the range of genome sizes known for Plantaginaceae (0.26–8.98 pg; N = 204 species in 18 genera, including Callitriche L., Penstemon Mitch., Plantago and Veronica ; Broderick et al ., ; Bennett & Leitch, ; Wong & Murray, ; Prančl et al ., ).…”

Distributions of vascular plants in the Czech Republic. Part 7

“…Other gaps on the map are due to under-recording rather than true absences of the species. Because of frequent misidentifications of Callitriche species, the distribution map was based solely on examined herbarium specimens and on plants determined using flow cytometry (Prančl et al 2014). Callitriche hamulata (Fig.…”

“…In addition to the flora of the Czech Republic changing, our knowledge of it has increased. Genera that have undergone recent taxonomic revisions include Callitriche (Prančl 2012, Prančl et al 2014 and Rubus (e.g. Krahulcová et al 2013, Velebil et al 2016, Király et al 2017.…”

Lantana camara L. (sensu lato): an enigmatic complex

“…Variation in chromosome numbers in genus Lantana encourages the use of genome size as a species-specific marker. Genome size has been well-applied to resolve notable species complexes such as Reynoutria (Mandák et al 2003); Knautia arvensis (Kolář et al 2009); Dryopteris carthusiana (Ekrt et al 2010); Callitriche (Prančl et al 2014) and, identification of invasive alien taxa (see Suda et al 2010). Further, documentation of population cytotype structure of the invasive genets and their geographical distribution is central to monitor complex constituents' invasion potential.…”