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 (>500km) and microgeographic (<100m) 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 100-550km 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.
Highlights
Asexual reproduction results in genetically identical offspring, but single-locus differences can be contributed by somatic mutations (Arnaud-Haond et al 2007)
Ecology and Evolution published by John Wiley & Sons Ltd
In genets from the six new populations, we found no evidence of null alleles, and no evidence of scoring errors from large allele dropout or stuttering at any of the nine microsatellite loci
Summary
Asexual reproduction results in genetically identical offspring, but single-locus differences can be contributed by somatic mutations (Arnaud-Haond et al 2007). Asexual reproduction is common along the margins of species’ distributions, and it has been suggested that this is a consequence of species hybridization, high physiological stress in marginal environments favouring certain genotypes (“frozen niche hypothesis”), or high costs of sexual reproduction in these habitats (Vrijenhoek 1984; Silvertown 2008; Bengtsson 2009; Vrijenhoek and Parker 2009). Asexual reproduction does not reduce single-locus genetic variation of populations; instead, it conserves existing genotypes by preventing a 2015 The Authors.
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