Intraspecific variation in seaweeds: The application of new tools and approaches

Authors: Wattier, R. and Maggs, C.A.

Journal: Advances in Botanical Research

Volume: 35

Pages: 171-212

ISSN: 0065-2296

DOI: 10.1016/s0065-2296(01)35007-3

Abstract:

Seaweeds, marine macroalgae that are individually visible to the naked eye, belong to three divisions, chlorophytes (green algae), chromophytes (brown algae) and rhodophytes (red algae), which are broadly convergent in morphology, yet represent a high proportion of eukaryotic diversity. Despite the commercial value of seaweeds, biodiversity is still poorly understood, particularly at the infraspecific level. Species-level taxonomy is still centred on the morphological species concept, which is increasing used in concert with other data, particularly molecular analyses, although phycologists are still not sufficiently confident in the relatively new fields of molecular taxonomy and phylogenetic systematics. Seaweeds show an extraordinary diversity of life histories and offer great potential to theorists interested in ecological and evolutionary processes. Population genetics has developed slowly in seaweeds compared to that for most other groups of conspicuous and economically important organisms primarily because of the problem, now largely overcome by technical developments, of isolating high-quality DNA from large numbers of individuals. Plastids are believed to be uniparentally inherited in seaweeds, so their use permits comparison and interpretation with well-developed mitochondrial markers in animals. The spacer between the genes for the large and small subunits of rubisco, used as a target for polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP), has recently been developed for four tropical red algal species, allowing the analysis of spatial genetic structure within populations and at macrogeographic scales. The most widely used marker for phylogeographic studies, ribosomal DNA internal transcribed spacer sequences, has provided new interpretations of seaweed biogeography but is unsuitable for population-level studies. Single-locus microsatellites, often described as the "marker of choice" for microevolutionary studies, have only recently been developed for one red, one green and three brown algae. This involved enormous expenditure of time and effort due to very low genomic frequencies of microsatellites and small proportions of polymorphic loci. Despite these severe difficulties, microsatellites have already proved to be extremely useful markers for the seaweed species for which they were available. They enabled studies of kinship and male gamete dispersal in Gracilaria gracilis, breeding system and spatial population structure in Cladophoropsis membranacea and Laminaria digitata, population structure in relation to possible ecotypic differentiation in Fucus serratus, and genetic neighbourhood size in Ascophyllum nodosum. Thus, despite the increasing interest in molecular studies during the last decade, assessment of intraspecific genetic biodiversity of seaweeds is still in its infancy. The most useful markers (microsatellites, AFLPs, intersimple sequence repeats and SSCPs), of which AFLPs and SSCPs seem to be the most promising, have been introduced into macroalgal studies only in the last 4 years. Because microsatellites are particularly difficult to develop for seaweeds, one major challenge of the next 10 years will be to seek alternative highly polymorphic single-locus/co-dominant nuclear markers as a substitute. © 2000.

Source: Scopus