Genetic affiliations of miniaturized species and morphotypes within the Fucus genus (Phaeophyceae, Fucales)

Abstract

In the North Atlantic members of the Fucus genus have an important ecological role, forming habitats in the littoral or upper sublittoral zones. A phylogeographic history with frequent hybridization and large phenotypical variation challenge a full systematic and taxonomic understanding of the genus. This study treats some miniaturized Fucus taxa; F. cottonii, F. spiralis f. nanus and F. chalonii, and aims to determine their genetic affiliations using microsatellites. Samples were from Spain and Norway, with F. chalonii only sampled in Spain and F. cottonii in Norway. For microsatellite comparison, additional samples of F. vesiculosus and F. limitaneus were collected in Spain, and of F. vesiculosus and F. spiralis in Norway. Two samples of F. chalonii were analysed, and the results suggest that one sample had a close affiliation to F. spiralis f. nanus, and the other to F. vesiculosus. Individuals of both samples were dioecious. Two samples of F. cottonii were examined, where each was a multilocus genotype with the closest affiliation to F. vesiculosus. Each had a different allelic composition. This suggests they represent two clonal populations. An overall excess of heterozygosity, and occurrence of three alleles at two loci in one of the samples, may suggest that the two clones could have triploid origins. The two samples of Fucus spiralis f. nanus (from Norway and Spain) had very high FIS values, suggesting they represent very isolated and inbred populations of F. spiralis. The sample of F. spiralis f. nanus from Norway was assigned to one of the two genetic clusters found in F. spiralis. The results allow omitting the forma nanus as a taxonomic category for F. spiralis. Both F. chalonii and F. cottonii can have multiple affiliations, and the informal taxonomic category ‘species aggregate’ is suggested for both.