Population Genomic Analysis of the Origin and Adaptive Evolution of Invading Yellow Starthistle

Invasive species provide excellent models for studying the genetic basis of rapid evolutionary change during colonization of new environments. Evolutionary increases in size may be facilitating the invasion of yellow starthistle (Centaurea solstitialis), an aggressive rangeland weed in the Americas. A population genomic analysis of yellow starthistle was conducted to identify the origins of invading populations and explore the sources and pervasiveness of adaptive alleles which are potentially facilitating invasions. We used Illumina-sequenced RAD tags to identify and type several thousand single nucleotide polymorphisms in individuals from a total of 37 populations in the native range (Eastern Europe, Caucasus, and Greece), naturalized range (Western Europe), and invaded range (North and South America). Three genetic clusters corresponded to major geographic regions in the native range, a fourth cluster consisted of individuals found in all geographic regions except for Greece, and a fifth cluster consisted of individuals found only in the naturalized and the invaded range. Preliminary results support the hypothesis that American populations originate from source population(s) in Spain. Western US populations had varying levels of admixture, which suggests a role for both multiple introductions and founder effects in shaping genetic diversity in the invaders. Future work will involve identifying loci under selection and tracking SNPs associated with quantitative trait loci for larger size in invading populations. This study will improve our understanding of the sources of adaptive variation which allow populations to rapidly evolve in response to novel and changing selective environments.