Contrasting Patterns of Genome Size Diversity in Island Endemic Artemisia (Asteraceae)

Premise of research. Genome size has cascading effects at nuclear, cell, and whole-organism levels, with consequences in the biology of the species. Large genomes impose higher metabolic and energetic costs, which might be exceedingly limiting for species to thrive under stressing environments, such as island archipelagos. Methodology. We mined online databases to collate available data on chromosome numbers and genome sizes in the genus Artemisia, which colonized Macaronesia and Hawaii archipelagos. We applied phylogenetic-based modeling approaches to reconstruct the evolution of these two traits to estimate ancestral states as well as the main mechanisms of change. Pivotal results. On the basis of extant chromosome data, our analyses discard polyploidy as a likely mechanism for speciation in Macaronesia or Hawaii. However, contrasting genome size patterns are found. Hawaiian endemics account for the smallest genomes in Artemisia, while those of Macaronesian endemics fall well above the average size in the genus. Conclusions. The evidence gathered in Artemisia indicates that, rather than genome downsizing, the presence of small genomes most likely predated colonization of Hawaii, which could have been key for a long dispersal from an Asian ancestor. Such a pattern does not hold in Macaronesia, which is relatively closer to mainland compared with Hawaii, hence suggesting that geographical isolation might reduce the likelihood of a large-genomed taxon to successfully colonize remote island archipelagos.