Small genome separates native and invasive populations in an ecologically important cosmopolitan grass

Abstract

Abstract. The literature suggests that small genomes promote invasion in plants, but little is known about the interaction of genome size with other traits or about the role of genome size during different phases of the invasion process. By intercontinental comparison of native and invasive populations of the common reed Phragmites australis, we revealed a distinct relationship between genome size and invasiveness at the intraspecific level. Monoploid genome size was the only significant variable that clearly separated the North American native plants from those of European origin. The mean Cx value (the amount of DNA in one chromosome set) for source European native populations was 0.490 AE 0.007 (mean AE SD), for North American invasive 0.506 AE 0.020, and for North American native 0.543 AE 0.021. Relative to native populations, the European populations that successfully invaded North America had a smaller genome that was associated with plant traits favoring invasiveness (long rhizomes, early emerging abundant shoots, resistance to aphid attack, and low C:N ratio). The knowledge that invasive populations within species can be identified based on genome size can be applied to screen potentially invasive populations of Phragmites in other parts of the world where they could grow in mixed stands with native plants, as well as to other plant species with intraspecific variation in invasion potential. Moreover, as small genomes are better equipped to respond to extreme environmental conditions such as drought, the mechanism reported here may represent an emerging driver for future invasions and range expansions.

Competition among native and invasive Phragmites australis populations: An experimental test of the effects of invasion status, genome size, and ploidy level

“…Further, the clones differed in ploidy levels (4x, 6x, 8x) and, for tetraploids of European origin, both EU‐native and NA‐invasive, also in genome size (small, large). North American native clones were represented only by four tetraploids with large genomes as the small genome was not detected in this group (Pyšek et al, ). In NA‐invasive and EU‐native groups, eight clones were used (see Table for the numbers of replicates for particular pairs of competitors).…”

“…One system that provides opportunities to focus on organizational levels below the species rank, such as subspecies, populations, or individual genotypes, is a dominant species of wetlands all over the world Phragmites australis (common reed, Poaceae; Meyerson & Cronin, ; Meyerson, Lambert, & Saltonstall, ; Packer, Meyerson, Skálová, Pyšek, & Kueffer, ). This grass makes an ideal model system to study invasions by particular populations representing distinct genotypes, with native and invasive populations coexisting within the same geographic range (Eller et al, ; Meyerson, Cronin, & Pyšek, ; Packer et al, ; Pyšek et al, ). Although the analogous situation has been described for other tall grass‐like species and grasses, such as in the Typha genus (Ciotir & Freeland, ) or for Phalaris arundinacea (Lavergne, Muenke, & Molofsky, ), respectively, and some forbs (e.g., Myriophyllum spicatum ; Zuellig & Thum, ), the common reed invasion in the North America is by far best researched with a great body of accumulated information providing a broad background for ongoing studies (Chambers, Meyerson, & Saltonstal., ; Eller et al, ; Meyerson, Cronin, & Pyšek, ; Packer et al, ).…”

“…Recently, more robust evidence has started to appear in the literature that small genomes promote invasion in plants by interacting with other traits (Meyerson, Cronin, & Pyšek, ; Pyšek et al, ) and that the role of genome size may differ during different phases of the invasion process, playing the major role in the naturalization stage (Kubešová et al, ). The mechanism underlying these analyses is that species with large genomes are less likely to be invasive (Suda et al, ).…”

“…For P. australis , monoploid genome size (i.e., the amount of DNA in one chromosome set of an organism that, unlike the holoploid genome size, varies independently of ploidy level; Suda et al, ) was the only significant variable that clearly separated the North American native plants from those of European origin. This indicates that European populations successfully invaded North America because, relative to native populations, they had a smaller genome, which was associated with plant traits favoring invasiveness (Pyšek et al, ). The current study builds on this background and is based on the following premises:…”

“…This is based on the suggestion that competition is generally considered an important mechanism of plant invasion (e.g., Daehler, ; Gioria & Osborne, ; Goldstein & Suding, ; Vilà, Williamson, & Lonsdale, ), together with other factors such as the availability of open niches, propagule pressure, and disturbances. (b) Invasive populations differ from native populations in a number of growth, physiological, and reproductive traits (Pyšek et al, ) that can be related to a small genome, an underlying characteristic separating both groups (Pyšek et al, ). (c) Based on this, we hypothesized that small genomes constitute a key advantage in a direct competition between invasive and native populations that is manifested through traits associated with genome size (Suda et al, ).…”