Genome size variation in Cactaceae and its relationship with invasiveness and seed traits

Because naturalized and invasive plant species have disproportionately smaller genome sizes compared to all angiosperms, genome size has been proposed as a general predictor of invasiveness. The family Cactaceae includes some of the most important invasive species worldwide, and it is one of the plant families with lowest number of genome size estimations. The main goal of this study was to explore possible correlations between genome size and invasiveness in Cactaceae, and between genome size and seed size and weight, traits previously linked with invasiveness. Propidium iodide flow cytometry was used to estimate the genome size from seeds (mostly) of 256 taxa of Cactaceae (32 of which are known to be invasive, and 13 are considered potentially invasive), and seed size, weight and mass were measured or obtained from previous work. Contrary to expectation, no significant differences were observed in genome size among categories of invasion, suggesting that genome size alone is not a reliable predictor of invasiveness in Cactaceae. Also, no correlations were observed between genome size and the studied seed traits when the whole dataset was considered. At a finer scale, in Opuntioideae, positive significant correlations were observed between genome size and the seed traits studied, and in Cacteae, the opposite trend was observed. Since Cactaceae species possess low rates of metabolism, selection towards traits linked with genome size may not have been favoured irrespective of the invasive strategy. The large number of genome size estimates reported in this study offers great opportunities for studying the evolution of genome size in this family and for exploring possible correlations between genome size and geographical, environmental and phenotypic traits.