| This research examines the evolutionary processes involved in plant invasions. I focus on Cynara cardunculus L., a taxonomic conglomerate of distinct thistle phenotypes and genotypes, a successfully invasive species complex. The species complex includes cultivated artichoke and cardoon, as well as two distinctly different artichoke thistle phenotypes (Cynara cardunculus var. scolymus, artichoke, and Cynara cardunculus var. altilis, cardoon, Cynara cardunculus var. sylvestris, artichoke thistle). Native to the Mediterranean basin, its introduction into California is widely believed concurrent with Italian immigration. Due to morphological variability, present day California populations were suspected of infraspecific hybrid ancestry. I collected samples from throughout California, and compared them to those from Spain and Italy, as well as to greenhouse grown cultivars, using nuclear microsatellite markers and phenotypic traits. Results show California populations are neither Italian in origin, nor predominately hybrid-derived. Rather, the majority of populations show predominately Iberian genotypic ancestry, with introgression of Italian and cultivar alleles, likely the result of multiple introductions. Additionally, one third of all populations believed to be artichoke thistle were identified as feral artichoke. Although population differentiation is a key feature in both California and Italy, isolation by distance does not account for this structure in California but is strongly significant in Italy. Spanish populations showed evidence of gene flow overcoming drift, and isolation by distance was non-significant. In a common garden setting, California populations performed better than European populations for traits associated with competition and fitness. California's Iberian derived populations notably outperformed Spanish Iberian populations for the same traits. I conclude that feral artichoke is an invasion risk. I also propose the EICA for California artichoke thistle. I show how through the dual processes of dedomestication and EICA, California populations may be converging on a common invasive phenotype, despite their two distinctly different genotypes. |
