Pair-wise population matrix.

<p>Nei’s unbiased genetic distance (D) is shown below diagonal and values for population genetic differentiation (Φ_PT) are shown above diagonal. For abbreviations of populations, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129861#pone.0129861.t001" target="_blank">Table 1</a>. *P<0.05.</p

Principal component analysis performed from pairwise Nei’s genetic distances between populations.

<p>Orange asterisk: 2<i>x</i>; blue star: 4<i>x</i>; pink diamond: 6<i>x</i>; green dot: 8<i>x</i>. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129861#pone.0129861.t001" target="_blank">Table 1</a> for population codes.</p

The Polyploid Series of the Achillea millefolium Aggregate in the IberianPeninsula Investigated Using Microsatellites

The Achillea millefolium aggregate is one of the most diverse polyploid complexes of the Northern hemisphere and has its western Eurasian boundary in the Iberian Peninsula. Four ploidy levels have been detected in A. millefolium, three of which have already been found in Iberia (diploid, hexaploid and octoploid), and a fourth (tetraploid) reported during the preparation of this paper. We collected a sample from 26 Iberian populations comprising all ploidy levels, and we used microsatellite markers analyzed as dominant in view of the high ploidy levels. Our goals were to quantify the genetic diversity of A. millefolium in the Iberian Peninsula, to elucidate its genetic structure, to investigate the differences in ploidy levels, and to analyse the dispersal of the species. The lack of spatial genetic structure recovered is linked to both high levels of gene flow between populations and to the fact that most genetic variability occurs within populations. This in turn suggests the existence of a huge panmictic yarrow population in the Iberian Peninsula. This is consistent with the assumption that recent colonization and rapid expansion occurred throughout this area. Likewise, the low levels of genetic variability recovered suggest that bottlenecks and/or founder events may have been involved in this process, and clonal reproduction may have played an important role in maintaining this genetic impoverishment. Indeed, the ecological and phenologic uniformity present in the A. millefolium agg. in Iberia compared to Eurasia and North America may be responsible for the low number of representatives of this complex of species present in the Iberian Peninsula. The low levels of genetic differentiation between ploidy levels recovered in our work suggest the absence of barriers between them

Populations of <i>Achillea millefolium</i> investigated in the present study.

<p>K: chromosome count; S: stomatal size. Altitudes are expressed in meters above sea level.</p

Selected metaphases of the four ploidy levels.

<p>A) Diploid plate with 2<i>n</i> = 18 (pop. Gi1); B) Hexaploid plate with 2<i>n</i> = 54 (pop. Sa2); C) Octoploid plate with 2<i>n</i> = 72 (pop. Cs1); D) Tetraploid plate with 2<i>n</i> = 36 (pop. Pa1). Scale bar = 10 μm</p

Percentage assignment of each individual (represented by vertical bars) to each of the three genetic clusters (represented by different colours) inferred by the program Structure [43].

<p>See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129861#pone.0129861.t001" target="_blank">Table 1</a> for population codes.</p

Mantel test correlating geographic distance and genetic distance.

<p>Results of the IBD test searching for a correlation between geographic distance and genetic distance.</p

Pair-wise ploidy matrix.

<p>Nei’s unbiased genetic distance (D) is shown below diagonal and values for genetic differentiation (Φ_PT) are shown above diagonal. *P<0.05.</p

Percentage of individuals that belong to each of the seven genetic clusters (represented by different colours) inferred by the nonhierarchical K-means clustering analysis [46].

<p>Each vertical column corresponds to a population. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129861#pone.0129861.t001" target="_blank">Table 1</a> for population codes.</p

Screening for the most likely number of groups (K) with non-hierarchical K-means clustering [45], performed with 100000 independent runs for each value of K.

<p>The runs maximising ΔK values were initially considered as optimal (K = 7 and K = 12), and because K = 12 added little gain to ΔK, we kept K = 7 as the optimal final value.</p