Population genetics of Centaurea stoebe and C. diffusa in their native and introduced ranges

Abstract

When species are introduced into new ranges, they can proliferate to such an extent that they dominate the new community. Research on such biological invasions has focused on ecological changes in the invasive species and the invaded communities. Recently, there has also been interest in the evolutionary changes associated with biological invasions. I explored the population genetics of two species native to Eurasia that have invaded North America (Centaurea stoebe and C. diffusa) using microsatellite loci. I compared six codominant microsatellite loci to dominant inter simple sequence repeat (ISSR) markers in tetraploid C. stoebe. Microsatellites and ISSRs gave similar patterns of allelic diversity and population genetic structuring, though the magnitude of structure estimates was higher in ISSRs. ISSRs were the more cost effective method, but they were also more subjective and tended to overestimate population structure and underestimate heterozygosity. I investigated genetic diversity and population structure in native and invasive C. diffusa using five microsatellite loci. Allelic diversity and expected heterozygosity did not differ between ranges, indicating that a bottleneck in population size is unlikely to have occurred. Populations were more strongly structured in the invasive range than in the native range of C. diffusa, and there was no pattern of isolation by distance in either range. This pattern is suggestive of panmixia in the native range and of long-range dispersal within the invasive range. Assignment tests and phenetic trees indicate that C. diffusa may have been introduced into North America multiple times. I investigated genetic diversity and population structure in native and invasive C. stoebe (diploid subspecies C. s. stoebe and tetraploid subspecies C. s. micranthos) using six microsatellite loci. Genetic diversity was not reduced in the invasive range, suggesting that C. stoebe escaped genetic bottlenecks during colonization. Populations were genetically structured in both ranges of the species, and in the native range there was isolation by distance. A hypothesis of multiple introductions is supported by assignment tests. These results shed light on invasion pathways for these species and may form a base of knowledge for future hypotheses regarding the invasive success of spotted and diffuse knapweed.