Complex spatial clonal structure in the macroalgae Fucus radicans with both sexual and asexual recruitment

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.

Reciprocal transplants support a plasticity-first scenario during colonisation of a large hyposaline basin by a marine macro alga

“…In the northern Baltic Sea, by contrast, adventitious branches form, fall off and develop rhizoids that reattach them to the substratum, and from there they grow clonal copies of the mother thallus. Formation of adventitious branches was most frequent in F. radicans , less frequent in the Baltic Sea F. vesiculosus , and least common or absent in North Sea F. vesiculosus in our experiments, which correlates to the prevalence of clones in these populations (this study and [32]). Asexual reproduction by means of re-attaching adventitious branches seems to be a unique trait to the Baltic Sea that in itself has promoted the spread and establishment in a new area.…”

Baltic Sea genetic biodiversity: Current knowledge relating to conservation management

“…Within‐season genetic differences at herring spawning sites are interpreted as genetically different populations using the same spawning grounds (spawning waves; Jørgensen, Hansen, Bekkevold, Ruzzante, & Loeschcke, ; Jørgensen, Hansen, & Loeschcke, ). Short‐term genetic changes indicating drift have been observed in the species with low effective sizes (Table ) and also in turbot and narrow wrack (Ardehed et al, ; Florin & Höglund, ).…”

Fire coral clones demonstrate phenotypic plasticity among reef habitats

“…The genotype diversity (>1,000 genotypes) observed in this study is the highest ever documented for terrestrial or marine populations. Most studies assessing genetic variation in partially clonal organisms are not spatially explicit (Arnaud‐Haond et al., ; Gorospe, Donahue, & Karl, ; Schwartz & McKelvey, ), are based on sampling few individuals (~50) (Adjeroud et al., ; Ardehed et al., ; Becheler, Benkara, Moalic, Hily, & Arnaud‐Haond, ) or involve sampling of a single habitat (Gorospe & Karl, ). Such studies may therefore underestimate genotype diversity in clonal populations.…”