Ramsey J, Robertson A, Husband BC. Rapid adaptive divergence in New World Achillea, an autopolyploid complex of ecological races. Evolution 62: 639-653

Department of Integrated Biology, University of Guelph, 488 Gordon St, Guelph, ON N1G 2W1, Canada.
Evolution (Impact Factor: 4.61). 04/2008; 62(3):639-53. DOI: 10.1111/j.1558-5646.2007.00264.x
Source: PubMed


Adaptive evolution is often associated with speciation. In plants, however, ecotypic differentiation is common within widespread species, suggesting that climatic and edaphic specialization can outpace cladogenesis and the evolution of postzygotic reproductive isolation. We used cpDNA sequence (5 noncoding regions, 3.5 kb) and amplified fragment length polymorphisms (AFLPs: 4 primer pairs, 1,013 loci) to evaluate the history of ecological differentiation in the North American Achillea millefolium, an autopolyploid complex of "ecological races" exhibiting morphological, physiological, and life-history adaptations to diverse environments. Phylogenetic analyses reveal North American A. millefolium to be a monophyletic group distinct from its European and Asian relatives. Based on patterns of sequence divergence, as well as fossil and paleoecological data, colonization of North America appears to have occurred via the Bering Land Bridge during the Pleistocene (1.8 MYA to 11,500 years ago). Population genetic analyses indicate negligible structure within North American A. millefolium associated with varietal identity, geographic distribution, or ploidy level. North American populations, moreover, exhibit the signature of demographic expansion. These results affirm the "ecotype" concept of the North American Achillea advocated by classical research and demonstrate the rapid rate of ecological differentiation that sometimes occurs in plants.

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    • "In California, Achillea millefolium L. (Asteraceae) is one of the few native species that is able to coexist with the widespread invasive perennial grass Holcus lanatus (Poaceae), and also one of the few native species that is able to apply a competitive effect on H. lanatus (Muir 2009). Achillea millefolium is palearctic, and a phylogeographic analysis places BMR populations in a clade that colonized North America via the Bering Land Bridge during the Pleistocene (Ramsey et al. 2008). Over the last century, H. lanatus, a Eurasian native, has successfully established on several continents and is now found throughout the United States (Watt 1978; USDA NRCS 2010). "
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    • "C for 1 min; completion of these cycles was followed by a final extension of 72 C for 10 min. Clean-up was performed as described by Ramsey et al. (2008). Sequencing reactions were performed in a 12.5 mL volume that included 1.5 mL purified PCR product, 0.02 mL of primer (100 mM stock, 0.2 mM final concentration), 0.5 mL 5M ultrapure betaine (USB, Cleveland, Ohio), 2.5 mL Big Dye buffer (Applied Biosystems, Foster City, California) and 0.5 mL Big Dye (version 3.1; Applied Biosystems). "
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