AFLP analyses demonstrate genetic divergence, hybridization, and multiple polyploidization in the evolution of<i>Achillea</i>(Asteraceae‐Anthemideae)

Guo, Yanping; Saukel, Johannes; Mittermayr, R.; Ehrendorfer, Friedrich

doi:10.1111/j.1469-8137.2005.01315.x

Cited by 104 publications

(116 citation statements)

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“…Achillea borealis belongs to the Achillea millefolium aggregate, a circumpolar group of 15 species (30,45). Phylogenetic analyses indicate that Achillea colonized the New World in the recent geologic past (Pleistocene) via the Alaskan land bridge (30).…”

Section: Discussionmentioning

confidence: 99%

Polyploidy and ecological adaptation in wild yarrow

Ramsey

2011

Proc. Natl. Acad. Sci. U.S.A.

354

388

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Chromosome evolution in flowering plants is often punctuated by polyploidy, genome duplication events that fundamentally alter DNA content, chromosome number, and gene dosage. Polyploidy confers postzygotic reproductive isolation and is thought to drive ecological divergence and range expansion. The adaptive value of polyploidy, however, remains uncertain; ecologists have traditionally relied on observational methods that cannot distinguish effects of polyploidy per se from genic differences that accumulate after genome duplication. Here I use an experimental approach to test how polyploidy mediates ecological divergence in Achillea borealis (Asteraceae), a widespread tetraploid plant with localized hexaploid populations. In coastal California, tetraploids and hexaploids occupy mesic grassland and xeric dune habitats, respectively. Using field transplant experiments with wild-collected plants, I show that hexaploids have a fivefold fitness advantage over tetraploids in dune habitats. Parallel experiments with neohexaploids-first-generation mutants screened from a tetraploid genetic background-reveal that a 70% fitness advantage is achieved via genome duplication per se. These results suggest that genome duplication transforms features of A. borealis in a manner that confers adaptation to a novel environment.biogeography | ecological speciation | range boundary P olyploidy is a conspicuous and recurrent form of genetic variation in flowering plants (1-3). Since its discovery in the early 20th century, polyploidy has been postulated to mediate ecological differentiation, for three reasons. First, experimental polyploids in crop species exhibit altered morphological and growth characteristics (4-7). Second, in nature, closely related diploid and polyploid species have distinct geographic ranges (8, 9). Third, the occurrence of polyploidy varies across geographic regions, with highest incidences reported in alpine and arctic floras (10). Many evolutionists believe that polyploidy imbues plants with novel features that allow them to invade new environments or expand their geographic range (11)(12)(13)(14). This hypothesis, however, has not been tested rigorously. Ecological studies have traditionally focused on simple comparisons of diploids and naturally occurring polyploids that diverged in the distant past (15)(16)(17)(18)(19)(20). This approach confounds phenotypic differences caused by polyploidy with those caused by genic changes arising since the time of polyploid formation (21-23).Here I use an experimental approach to untangle the contributions of polyploidy per se to ecological divergence. Although sometimes regarded as a macroevolutionary event, genome duplication is an ongoing process in many plant populations (6, 24). First-generation polyploid mutants ("neopolyploids") form at rates equal to or exceeding the per locus mutation rate, and can thus be identified by en masse screening using flow cytometry (25,26). Because neopolyploids share a common genetic background with their diploid progenitors, the co...

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Section: Discussionmentioning

confidence: 99%

Polyploidy and ecological adaptation in wild yarrow

Ramsey

2011

Proc. Natl. Acad. Sci. U.S.A.

354

388

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“…Unreduced pollen formation has been reported in 4x F1 plants originated from experimental crosses between 2x × 4x parental cytotypes (Ehrendorfer 1959). This mechanism lead to regular and multiple gene flows from the 2x to the 4x level, even in the absence of 3x-F 1 (Guo et al 2005). The occurrence of large pollen grains (possibly 2n pollen grain) was observed along with smaller (normal) pollen grains in almost all of the following species A. millefolium, A. filipendulina, A. bieberstinii, A. tenuifolia, A. oxyodonta, A. vermicularis, A. santolina, A. eriophora and A. talagonia species (Sheidai et al 2009).…”

Section: A Tenuifoliamentioning

confidence: 99%

Karyotype analysis and new chromosome number reports in Achillea species

et al. 2012

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Cytological analyses were performed in nineteen accessions belonging to seven Achillea species. The results indicate that two species, A. filipendulina and A. tenuifolia, are diploid (2n = 2x = 18) and three species, A. bieberstinii, A. pachycephala, and A. aucheri are tetraploid (2n = 4x = 36). For two latter species, the chromosome numbers are new. Two ploidy levels of 2n = 6x = 54 and 2n = 8x = 72 in A. millefolium and two ploidy levels of 2n = 2x = 18 and 2n = 4x = 36 in A. santolina species were found. Cluster analysis based on chromosomal characteristics and karyotype asymmetry indices clustered the studied genotypes into three major groups. The first group included the diploid species (A. filipendulina, A. santolina and A. tenufolia), while the second group comprised tetraploid species (A. santolina, A. aucheri and A. pachycephala). A. millefolium (hexaploid, octaploid) and A. bieberstinii (tetraploid) were classified in the third group. Total form percentage (TF%) in groups 1, 2 and 3 were 42.03, 42.15 and 41.08, respectively. Group 1 possessed the highest average of symmetry index (S% = 70.8). Stebbins classification method grouped all accessions in class A. Moreover, group 1 (diploid level species), had the most symmetric karyotype from point of view of centromere and chromosome length. Therefore, it can be concluded that the genotypes belonging to group 1 are the earliest evolutionary form.

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“…Guo et al, 2004). Although the genus has a predominately Old World distribution, phylogenetic studies indicate that an autotetraploid lineage of the circumpolar A. millefolium aggregate colonized North America approximately 1 Mya (Guo et al, 2005;Ramsey, unpublished data). In a rapid radiation, these tetraploids evolved a diversity of ecological races (widespread across North America) as well as local occurrences of autohexaploids (restricted to the Pacific states and provinces of the United States and Canada) (Clausen et al, 1940(Clausen et al, , 1948Lawrence, 1947;Tyrl, 1975).…”

Section: Introductionmentioning

confidence: 99%

Unreduced gametes and neopolyploids in natural populations of Achillea borealis (Asteraceae)

2006

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Polyploidy is a major mechanism of speciation and adaptation, yet little is known about the origins of polyploids in natural species. I investigated gametic nonreduction and neopolyploid formation in natural tetraploid populations of Achillea borealis (Asteraceae), an autopolyploid complex consisting of tetraploid and hexaploid cytotypes. Cytological analyses of tetraploid populations revealed the occurrence of reduced (n ¼ 2x) as well as unreduced 'big' (2n ¼ 4x) and 'jumbo' (4n ¼ 8x) pollen grains, which were clearly distinguished by size. Production of unreduced pollen was monitored in two tetraploid populations in 1997 and 1998. Mean population-level frequencies of unreduced pollen ranged from 0.030 to 0.538%, with as few as one-third and as many as one-half of sampled plants producing unreduced grains. Eight individuals were found to produce 41% unreduced pollen, with highest observed frequencies of 7.0, 13.2 and 15.8%. Experimental crosses using high unreduced pollen producers as male parents generated viable seeds. However, the frequency of neohexaploids in the progeny of experimental crosses (0.388%) was similar to that observed in progeny of randomly selected, openpollinated control parents (0.465%). These results suggest that unreduced eggs are the most likely source of new polyploids. In spite of the inefficiency of unreduced pollen in unilateral sexual polyploidization, the overall rate of neohexaploid formation (one in 233) was several orders of magnitude greater than estimates of genic mutation rates.

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AFLP analyses demonstrate genetic divergence, hybridization, and multiple polyploidization in the evolution ofAchillea(Asteraceae‐Anthemideae)

Cited by 104 publications

References 78 publications

Polyploidy and ecological adaptation in wild yarrow

Polyploidy and ecological adaptation in wild yarrow

Karyotype analysis and new chromosome number reports in Achillea species

Unreduced gametes and neopolyploids in natural populations of Achillea borealis (Asteraceae)

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