Conservation and polymorphism of mitochondrial intergenic sequences in brown algae (Phaeophyceae)

Abstract

Due to their haploid nature, uniparental inheritance and apparent absence of recombination, organellar DNA markers are ideal tools for studying both intraspecific and interspecific phylogenies. Although ‘universal’ cytoplasmic DNA primers have become available for both red and green seaweeds, they are not transferable to brown seaweeds. Thus, based on the sequence of mitochondrial genome of the kelp Laminaria digitata, we developed universal-type primers for seven intergenic spacer loci and one mononucleotide tandem repeat locus. We investigated the conservation and sequence variation of these loci among nine Laminarialean and three fucoid species, as well as intraspecific polymorphism within five of these species. Six loci were conserved in at least four of the five brown algal families tested and five were polymorphic within at least one species. Although overall levels of divergence were relatively homogenous (π = 0.314 ± 0.031), a hierarchical analysis suggests there is variation in the rate of evolutionary change among the six intergenic spacers. Due to their high degree of transferability, versatility and to non-coding nature, we argue that these intergenic spacer loci are highly efficient markers for within-family phylogenetic studies and for intra-specific phylogeographic studies in brown seaweeds.