ARS | Publication request: Multiple introductions of invasive Centaureas inferred from cpDNA haplotypes

Submitted to: Diversity and Distributions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 15, 2008
Publication Date: March 1, 2008
Citation: Hufbauer, R.A., Sforza, R. 2008. Multiple introductions of invasive Centaureas inferred from cpDNA haplotypes. Diversity and Distributions. 14:252-261.

Interpretive Summary: Biological invasions are crucibles for rapid ecological and evolutionary change: they alter species distributions, ecosystem processes, and community structure, and are a key threat to native biodiversity The genus Centaurea L. (Asteraceae) has about 300 species, many of which have been introduced around the world and become invasive. In North America, 34 Centaurea species are reported to be introduced, 14 of which are defined as noxious weeds in one or more states. However, there is uncertainty regarding exactly which taxa are present in North America, To move towards rigorous tests of hypotheses to explain and manage biological invasions, we are exploring the population genetics of the invasion of C. diffusa and C. stoebe micranthos into North America. We gathered sequence data from chloroplast introns to evaluate the region’s utility and to explore: (1) whether the two species were introduced one or more times into North America, (2) possible origins in the native range of invasive individuals, and (3) levels of genetic variation within the native and introduced ranges. Our results suggest an ongoing hybridization between the species or incomplete segregation, that can guide further exploration for the origins of these species.

Technical Abstract: Knowing the origin of invasive taxa, whether multiple introductions have occurred, and levels of genetic variation relative to the native range, is vital to conducting rigorous tests of hypotheses to explain biological invasions. We explore phylo- geographical relationships of two Eurasian knapweed taxa that are invasive in North America, Centaurea diffusa and C. stoebe micranthos (Asteraceae), using chloroplast DNA intron sequences. We also gathered data from C. stoebe stoebe, hybrids between C. diffusa and C. stoebe stoebe (C. xpsammogena), and three other species in the genus. We sequenced 213 individuals from Eurasia and North America, and found 22 haplotypes. Centaurea diffusa has lower haplotype diversity and allelic richness in the introduced range relative to the native range. Even with reduced variation, the data suggest at least two introductions of C. diffusa. There is a trend towards reduced variation in C. stoebe micranthos, but it is not significant. One of the haplotypes found in North American C. stoebe micranthos matches a haplotype from a taxon other than C. stoebe micranthos in Europe. This suggests introgression of the chloroplast between taxa, or possibly the invasion of another Centaurea taxon into North America. Additionally, C. diffusa, C. stoebe micranthos, and C. stoebe stoebe share several haplotypes, including their most common haplotype. This suggests ongoing hybridization between the species or incomplete segregation. These data can guide further exploration for the origins of these species, and point out locations within the introduced range with unique and diverse genetic makeup.