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. 2015 Sep 9;5(19):4233-45.
doi: 10.1002/ece3.1629. eCollection 2015 Oct.

Complex Spatial Clonal Structure in the Macroalgae Fucus Radicans With Both Sexual and Asexual Recruitment

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Free PMC article

Complex Spatial Clonal Structure in the Macroalgae Fucus Radicans With Both Sexual and Asexual Recruitment

Angelica Ardehed et al. Ecol Evol. .
Free PMC article

Abstract

In dioecious species with both sexual and asexual reproduction, the spatial distribution of individual clones affects the potential for sexual reproduction and local adaptation. The seaweed Fucus radicans, endemic to the Baltic Sea, has separate sexes, but new attached thalli may also form asexually. We mapped the spatial distribution of clones (multilocus genotypes, MLGs) over macrogeographic (>500 km) and microgeographic (<100 m) scales in the Baltic Sea to assess the relationship between clonal spatial structure, sexual recruitment, and the potential for natural selection. Sexual recruitment was predominant in some areas, while in others asexual recruitment dominated. Where clones of both sexes were locally intermingled, sexual recruitment was nevertheless low. In some highly clonal populations, the sex ratio was strongly skewed due to dominance of one or a few clones of the same sex. The two largest clones (one female and one male) were distributed over 100-550 km of coast and accompanied by small and local MLGs formed by somatic mutations and differing by 1-2 mutations from the large clones. Rare sexual events, occasional long-distance migration, and somatic mutations contribute new genotypic variation potentially available to natural selection. However, dominance of a few very large (and presumably old) clones over extensive spatial and temporal scales suggested that either these have superior traits or natural selection has only been marginally involved in the structuring of genotypes.

Keywords: asexual reproduction; clonality; macroalgae; microsatellites; somatic mutations.

Figures

Figure 1
Figure 1
Geographic positions of the 16 analyzed populations of Fucus radicans, and an illustration of Fucus radicans.
Figure 2
Figure 2
Microgeographic distribution of multilocus genotypes (MLGs; A–C) and multilocus lineages (MLLs; see text for definition; D–F) in two geographic dimensions (x and y with axes indicating distances in meters from an arbitrary reference point 0,0) in three Swedish localities, N, O, and P (see Table 1 and Fig. 1). The sex of each individual is indicated (circle – female; triangle – male), while color represents distinct MLGs and MLLs, respectively. Note that the same colors are used also in Figures 4 and 5, with white and black indicating clones that exist only in a local site and gray indicating unique MLGs (singletons).
Figure 3
Figure 3
Spatial autocorrelation analysis of kinship coefficients for F. radicans in populations Swe N (A), Swe O (B), and Swe P (C). Each of the three correlograms shows both a ramet‐level analysis which includes all pairs sampled (coancestry F (ij) at the ramet level), a genet‐level analysis with only pairs of genets included (coancestry F (ij) at the genet level), and the probability of clonal identity, F (r), which estimates the clonal subrange, all on the y‐axis. * and † indicate significant P‐values for genet and ramet level, respectively.
Figure 4
Figure 4
Network of multilocus genotypes (MLGs) showing multilocus lineages (MLLs). Each circle represents a separate MLG, and each color indicates a separate MLL (colors as in Figs 2 and 5). Circle size is proportional to numbers of individuals, and figures on scale reflect numbers of individuals of the largest MLG of each MLL. When present, letters indicate that sex was confirmed (F for female, M for male). MLGs are clustered into MLL by joining those MLGs that differ by 1–2 mutations.
Figure 5
Figure 5
Macrogeographic distribution of singletons (gray), local clones (black and white), and widespread clones (different colors) in the Baltic Sea (A). In (B), MLGs that differ with 1–2 mutations (see Fig. 3) are merged into multilocus lineages (MLLs). For details on sample sizes and positions, see Figures 1 and Table 1.

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