The hidden side of plant invasions: The role of genome-wide processes in plant success

Background/Question/Methods

Identifying the traits that distinguish invasive species from non-invasive species remains central to invasion biology. Invasive species can have higher trait performance than non-invasive species for traits related to physiology, leaf-area allocation, shoot allocation, growth rate, size and fitness, seed size, vegetative reproduction, and early flowering. It is assumed that genome size, ploidy level (cytological factors), and growth and reproductive traits (ecological factors) have a direct effect on invasiveness. Geographic origin may directly affect invasiveness by the variation in invasion potential of individuals or clones acquired in their native range. The region where an invasion occurs has direct effects, due to regional variation in community and habitat invasibility, climatic conditions and disturbance. Cytological and geographical factors are also assumed to have indirect effects on invasiveness by influencing ecological factors. The characteristics of an organism’s genome, e.g. ploidy level and genome size, are important biodiversity attributes that influence many traits at different levels of biological organization and are therefore of great interest to invasion ecology. Using flow cytometry, we quantified variation in plant nuclear genome size through a cytological analysis of the genus Phragmites and asked whether genome size is structured geographically in the native and introduced ranges of its distribution.

Results/Conclusions

From fresh tissue samples collected in North America, we found significant differences between the genome sizes of P. australis for North American native, Eurasian introduced, and Gulf Coast populations ranging from 2.18 pg for the smallest genome sizes in the introduced Eurasian lineage to 3.56 pg for Gulf Coast populations. Preliminary analysis of dried tissue samples analyzed from the global Phragmites collection at Aarhus University included populations from Europe, Mediterranean region, Asia, Australia, South America and Africa. Results revealed five distinct genome size groupings with a 3.23-fold variation in genome size across the groups. Together these analyses provide evidence for high variability in genome size within P. australis and across the Phragmites genus and suggest that at least in North America, invasive genotypes of P. australis may have smaller DNA contents than other sympatric lineages. In 1996, Rejmánek hypothesized that small genome size could result from selection for rapid plant generation times and therefore might be associated with plant invasiveness. Our results support this and we suggest that the amount of nuclear DNA in invasive plants may be of paramount ecological and evolutionary importance by leading to genetic novelties and to the establishment of pheno-/genotypes with enhanced invasive ability.