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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    ABSTRACT: Invasive species may undergo rapid change as they invade. Native species persisting in invaded areas may also experience rapid change over this short timescale relative to native populations in uninvaded areas. We investigated the response of the native Achillea millefolium to soil from Holcus lanatus-invaded and uninvaded areas, and we sought to determine whether differential responses between A. millefolium from invaded (invader experienced) and uninvaded (invader naïve) areas were mediated by soil community changes. Plants grown from seed from experienced and naïve areas responded differently to invaded and uninvaded soil with respect to germination time, biomass, and height. Overall, experienced plants grew faster and taller than their naïve counterparts. Naïve native plants showed negative feedbacks with their home soil and positive feedbacks with invaded soil; experienced plants were less responsive to soil differences. Our results suggest that native plants naïve to invasion may be more sensitive to soil communities than experienced plants, consistent with recent studies. While differences between naïve and experienced plants are transgenerational, our design cannot differentiate between differences that are genetically based, plastic, or both. Regardless, our results highlight the importance of seed source and population history in restoration, emphasizing the restoration potential of experienced seed sources.
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    • "DISCUSSION The results obtained at the three spatial scales studied indicate relatively strong genetic separation between diploid and hexaploid cytotypes of A. amellus. This contrasts with many previous studies on diploid–polyploid systems, in which either frequent gene flow or broad shared ancestral polymorphisms among cytotypes has been reported (for example, Ramsey et al., 2008; Fehlberg and Ferguson, "
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    ABSTRACT: The potential for gene exchange across ploidy levels has long been recognized, but only a few studies have explored the rate of gene flow among different cytotypes. In addition, most of the existing knowledge comes from contact zones between diploids and tetraploids. The purpose of this paper was to investigate relationships between diploid and hexaploid individuals within the Aster amellus aggregate. A. amellus is known to occur in diploid and hexaploid cytotypes in Europe, with a complex contact zone in central Europe. Patterns of genetic diversity were investigated using seven microsatellite loci at three different spatial scales: (1) in the single known mixed-ploidy population; (2) in populations at the contact zone and (3) in a wider range of populations across Europe. The results show clear separation of the cytotypes at all three spatial scales. In addition, analysis of molecular variance strongly supported a model predicting a single origin of the hexaploids, with no or very limited gene flow between the cytotypes. Some hexaploid individuals found in the mixed-ploidy population, however, fell into the diploid cluster. This could suggest recurrent polyploid formation or occasional cross-pollination between cytotypes; however, there are strong post-zygotic breeding barriers between the two cytotypes, making the latter less plausible. Overall, the results suggest that the cytotypes could represent two cryptic species. Nevertheless, their formal separation is difficult as they cannot be distinguished morphologically, occupy very similar habitat conditions and have largely overlapping distribution ranges. These results show that polyploid complexes must be treated with caution as they can hide biological diversity and can have different adaptation potentials, evolving independently.Heredity advance online publication, 21 November 2012; doi:10.1038/hdy.2012.87.
    Full-text · Article · Nov 2012 · Heredity
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    • "assessed using fi ve microsatellite loci developed in our laboratory: PHL28, PHL33, PHL68, PHL98, and PHL113 ( Fehlberg et al., 2008 ). Primer sequences for PHL28 are as follows: forward (5 ′ -GTTGCCACCTCACAGATTCC-3 ′ ) and reverse (5 ′ -AATTGGGCGGTAAAAATGAA-3 ′ ). Primer sequences for PHL33, PHL68, PHL98, and PHL113 are described by Fehlberg et al. (2008) . Amplifi cation products from each locus for several individuals were cloned and sequenced to confi rm that the intended microsatellite locus was being amplifi ed. General amplifi cation and genotyping procedures followed that described by Fehlberg et al. (2008) . When microsatellite loci are genotyped in polyploid individuals that are"
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