Abstract
Plant invasions are recognized as major drivers of ecosystem change, yet the precise cause of these invasions remains unknown for many species. Frequency and modes of introductions during the first, transport and colonization, stages of the invasion process as well as phenotypic changes due to plasticity or changing genetic diversity and adaptation during later establishment and expansion stages can all influence the “success” of invasion. Here, we examine some of these factors in, and the origin of, a very successful weed, Cichorium intybus (chicory) which was introduced to North America in the 18th century and which now can be found in all 48 continental U.S. states and much of Canada. We genotyped a Eurasian collection of 11 chicory cultivars, nine native populations and a North American collection of 20 introduced wild populations which span the species range (592 individuals in total). To detect the geographic sources of North American chicory populations and to assess the genetic diversity among cultivars, native, and introduced populations, we used both a sequenced cpDNA region and 12 nuclear simple sequence repeat (SSR), microsatellite loci. Four cpDNA haplotypes were identified and revealed clear geographic subdivisions in the chicory native range and an interspecific hybrid origin of Radicchio group. Nuclear data suggested that domesticated lines deliberately introduced to North America were major contributors to extant weedy populations, although unintended sources such as seed contaminants likely also played important roles. The high private allelic richness and novel genetic groups were detected in some introduced populations, suggesting the potential for local adaptation in natural sites such as deserts and nature reserves. Our findings suggest that the current populations of weedy U.S. chicory have evolved primarily from several sources of domesticated and weedy ancestors and subsequent admixture among escaped lineages.
Highlights
We genotyped cultivars, as well as wild Eurasian and North American chicory populations in order to assess the genetic diversity of this species, and to examine evolutionary changes since chicory was introduced to the United States in the late 1700s
& Brzyski, 2015). Chloroplast DNA (cpDNA) variation in populations is generally low, but it serves as a useful tool for monitoring seed dispersal and maternal contributions (Ennos, Sinclair, Hu, & Langdon, 1999; Wallace et al, 2011)
Breeding and cultivation of these plants terminates in a fixation of favored morphological and genetic differences distinguishing a domesticate from its wild progenitor (Pickersgill, 2007)
Summary
We genotyped cultivars, as well as wild Eurasian and North American chicory populations in order to assess the genetic diversity of this species, and to examine evolutionary changes since chicory was introduced to the United States in the late 1700s. The domesticated CC lines when compared to the wild EU, for which samples sizes were equivalent, possessed substantial levels of genetic diversity but were generally less polymorphic, had fewer alleles per locus, and higher inbreeding coefficients.
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