Abstract
The genus Anthoxanthum (sweet vernal grass, Poaceae) represents a taxonomically intricate polyploid complex with large phenotypic variation and its evolutionary relationships still poorly resolved. In order to get insight into the geographic distribution of ploidy levels and assess the taxonomic value of genome size data, we determined C- and Cx-values in 628 plants representing all currently recognized European species collected from 197 populations in 29 European countries. The flow cytometric estimates were supplemented by conventional chromosome counts.In addition to diploids, we found two low (rare 3x and common 4x) and one high (~16x–18x) polyploid levels. Mean holoploid genome sizes ranged from 5.52 pg in diploid A. alpinum to 44.75 pg in highly polyploid A. amarum, while the size of monoploid genomes ranged from 2.75 pg in tetraploid A. alpinum to 9.19 pg in diploid A. gracile. In contrast to Central and Northern Europe, which harboured only limited cytological variation, a much more complex pattern of genome sizes was revealed in the Mediterranean, particularly in Corsica. Eight taxonomic groups that partly corresponded to traditionally recognized species were delimited based on genome size values and phenotypic variation. Whereas our data supported the merger of A. aristatum and A. ovatum, eastern Mediterranean populations traditionally referred to as diploid A. odoratum were shown to be cytologically distinct, and may represent a new taxon. Autopolyploid origin was suggested for 4x A. alpinum. In contrast, 4x A. odoratum seems to be an allopolyploid, based on the amounts of nuclear DNA. Intraspecific variation in genome size was observed in all recognized species, the most striking example being the A. aristatum/ovatum complex.Altogether, our study showed that genome size can be a useful taxonomic marker in Anthoxathum to not only guide taxonomic decisions but also help resolve evolutionary relationships in this challenging grass genus.
Highlights
Great strides have been made in recent years in advancing our understanding of the role of recent and ancient genome duplication in the evolution of land plants, angiosperms [1,2,3]
We addressed the following questions: (1) Which ploidy levels can be found among European members of Anthoxanthum, based on representative geographic and taxonomic sampling? (2) What is the range of genome size variation, and how does it correspond to currently recognized taxonomic groups? (3) What is the value of genome size data as a species-specific marker for taxonomic purposes and an indicator of evolutionary relationships?
Our study provided novel insight into ploidy and genome size variation of all currently recognized European members of the genus Anthoxanthum, which we sampled across large geographic areas
Summary
Great strides have been made in recent years in advancing our understanding of the role of recent and ancient genome duplication in the evolution of land plants, angiosperms [1,2,3]. Perception of ploidy diversity in natural populations has been dramatically reshaped over the last two decades, after the advent and increased usage of DNA flow cytometry (FCM). This high-throughput analytical tool offers a rapid and precise method for estimating the amount of nuclear DNA across multiple populations and over large spatial scales [10,11]. Estimated genome size values allow ploidy levels to be inferred but may provide insights into evolutionary relationships and genome constitutions of investigated species [12]. Genome size may help resolve conflicting hypotheses about the origin of polyploids (auto- vs. allopolyploidy) and identify putative parental combinations in hybridogenous species [13,14,15,16,17,18]
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