Evolutionary and ecological implications of genome size in the North American endemic sagebrushes and allies (Artemisia, Asteraceae)

The genome size of 51 populations of 20 species of the North American endemic sagebrushes (subgenus Tridentatae), related species, and some hybrid taxa were assessed by flow cytometry, and were analysed in a phylogenetic framework. Results were similar for most Tridentatae species, with the exception of three taxonomically conflictive species: Artemisia bigelovii Gray, Artemisia pygmaea Gray, and Artemisia rigida Gray. Genome size homogeneity (together with the high morphological, chemical, and karyological affinities, as well as low DNA sequence divergence) could support a recent diversification process in this geographically restricted group, thought to be built upon a reticulate evolutionary framework. The Tridentatae and the other North American endemic Artemisia show a significantly higher genome size compared with the other subgenera. Our comparative analyses including genome size results, together with different kinds of ecological and morphological traits, suggest an evolutionary change in lifestyle strategy linked to genome expansion, in which junk or selfish DNA accumulation might be involved. Conversely, weed or invasive behaviour in Artemisia is coupled with lower genome sizes. Data for both homoploid and polyploid hybrids were also assessed. Genome sizes are close to the expected mean of parental species for homoploid hybrids, but are lower than expected in the allopolyploids, a phenomenon previously documented to be related with polyploidy.