Phylogenetic relationships within the Sphacelariales sensu stricto were investigated using both a molecular and a morphological approach. Twenty species were included, representing all three families (i.e. Cladostephaceae, Sphacelariaceae and Stypocaulaceae) and six of the eight genera. The outgroup consisted of six species representing the Syringodermatales, Dictyotales, Choristocarpaceae and Onslowiaceae. DNA sequences of partial rbcL [1255–1375 nucleotides (nt)] and the adjacent RUBISCO spacer (40–842 nt) were determined in order to assess the molecular phylogeny. Only the 3′-end of the spacer (112 nt positions) was alignable for the ingroup taxa. Partition homogeneity testing showed that rbcL and RUBISCO spacer sequences could be combined. However, analysis of rbcL alone or in combination with the RUBISCO spacer gave the same results with only slight differences in support (bootstrap, jackknife, decay). Support was low at the base of the ingroup. Four basal clades could be discerned: (1) Stypocaulaceae, (2) Sphacelaria radicans, (3) Sphacelaria caespitula and (4) all other included taxa: (Sphacella subtilissima+the Sphacelaria subgenus Propagulifera) and (Cladostephus spongiosus+Sphacelaria nana+the Sphacelaria subgenera Battersia+Pseudochaetopteris). The independent morphological analysis (using 23 unordered morphological characters) revealed high homoplasy and an almost completely unresolved tree in which only the subgenus Propagulifera was supported. The morphological characters were subsequently mapped onto the rbcL tree in order to identify diagnostic or phylogenetically informative characters. Blackening in response to bleach and the presence of secondary segments were found to be basal synapomorphies for the Sphacelariales; presence of propagules with a lenticular central apical cell defines the Propagulifera; and strict acroblastic branching mode and axillary zoidangia define the Stypocaulaceae. The remaining characters have been gained or lost multiple times. This study highlights the problem of extreme morphological convergence and/or plasticity. Four options for a new circumscription including nomenclatural changes are discussed. It is concluded that none of the options will lead to greater clarity with respect to either identification or classification.
In 1984, Caulerpa taxifolia (Vahl) C. Agardh was reported along the coast of Monaco. Over the past decade it has spread along 60 km of the Mediterranean coastline and presently represents a potential risk to biodiversity. Several explanations have been advanced regarding the presence of C. taxifolia in the Mediterranean. One hypothesis maintains that the alga was introduced accidentally into the sea at Monaco, where it has been used as a decorative alga in aquaria. Caulerpa taxifolia has not been reported in earlier marine floras of the Mediterranean, and its sudden appearance has suggested that it may be a recent introduction. Another hypothesis proposes that C. taxifolia and Caulerpa mexicana Sonder ex Kützing are morphological variants of one another and hence conspecific taxa. Caulerpa mexicana has been found in the eastern Mediterranean since at least 1941. In order to establish the taxonomic identities of these taxa, individuals from five populations of C. taxifolia and four populations of C. mexicana were collected from within and outside of the Mediterranean. Comparative DNA sequence analysis of the nuclear ribosomal cistron, including the 3′‐end of the 18S, ITS1, 5.8S, and ITS2 regions, show clear phylogenetic separation of the two taxa using parsimony and maximum likelihood analyses. Separation is maintained whether the analyses are based on just the more conserved 18S data or just the fast‐ evolving spacers. The two species are thus not conspecific. For specimens of uncertain identity (i.e. taxifolia–mexicana intermediates), a PCR diagnostic amplification can easily be performed because the ITS1 in C. taxifolia is 36 nucleotides shorter than the ITS1 in C. mexicana. Whether or not C. taxifolia has been present for a longer period of time in the marine flora, either as a cryptic endemic species or as the result of one or more introductions, represents an additional hypothesis that will require identification of biogeographic populations from throughout the world, as well as a population‐level study of the Mediterranean region.
Abstract Genotypic relationships between a number of Anabaena strains, belonging to different species, were determined by means of comparison of their DNA base composition, DNA-DNA reassociation rates, thermal stability values of DNA-DNA hybrids, and electrophoretic behaviour of five different enzymes. In order to compare these relationships with morphological relationships between the strains tested, a numerical analysis of morphological traits was performed. DNA base compositions appeared to be almost identical. Intraspecific DNA DNA hybridizations showed high renaturation rates and high thermal stability values of hybrids, indicating a high degree of similarity of genomes of strains belonging to one species. Interspecific DNA-DNA hybridizations showed considerably lower renaturation rates and thermal stabilities, indicating considerable interspecific genetic differences. Electrophoretic patterns of enzymes more or less confirmed these findings, but also showed intraspecific differences. In general the results demonstrate that morphological similarities and differences between Anabaena strains are correlated with genetic similarities and differences, respectively.
Phormidium, Plectonema, Lyngbya and Synechococcus strains from freshwater- and marine habitats were incubated in media with different concentrations of seawater, under different light intensities and temperatures, submitted to different desiccation procedures, tested for endolithic growth in shells and grown on two different media solidified with agar. On the basis of the observed differences in halotolerance, cell dimensions and the reaction pattern with regard to the other parameters used, three taxa, existing at about species level, could be recognized within those strains which were identified as Schizothrix calcicola sensu Drouet. Characters as false branching and sheath morphology could not be used for the distinction between these taxa. The results also led to the conclusions that two other strains, which belong to the Drouet species Microcoleus lyngbyaceus, are no ecophenes of each other. The two coccoid Synechococcus strains could be ranked under two different species. The results are discussed with regard to Drouet's species concept within the Cyanophyceae. It is suggested to determine the genotypic relationships between the strains used, as a verification of the usefulness of the morphological and ecological characters involved in the delimitation of the different taxa recognized.
Ascophyllum nodosum is dominant seaweed along many rocky intertidal shores throughout the North Atlantic. Next to the kelps, fucalean taxa such as Ascophyllum are the largest macrophytes and provide important habitat for invertebrates. Understanding the underlying genetic structure of natural populations over a range of spatial scales can reveal how the causes of structure may change with scales. Separating population history from population structure may also be elucidated. The analysis is based on six polymorphic microsatellite loci and> 1000 individuals. Strong genetic structure at small spatial scale was found and is consistent with demographic models based on long‐lived individuals, low recruitment and many sib matings. At large spatial scales only weak population differentiation was found. This is consistent with recent recolonization of the North Atlantic following the last glacial maximum.
The seaweed Cladophoropsis membranacea (Hofman Bang ex. C. Agardh) Børgesen is a widely distributed species on coral reefs and along rocky coastlines throughout the tropics and subtropics. In a recent population-level survey openface>1600 individuals with eight microsatellite loci, a number of isolates from biogeographically disjunct locations could not be amplified for any of the loci. Nonamplifiable and amplifiable isolates co-occurred within the Canary Islands, Cape Verde Islands, and in the Caribbean. These unexpected results led to question whether or not C. membranacea is a single species. Phylogenetic relationships were evaluated using rDNA ITS1 and ITS2 sequence comparisons from 42 isolates sampled from a subset of 30 of the 66 locations. Four well-supported clades were identified. Sequence divergence within clades was <1%, whereas between-clade divergence was 2%–3%. Intraindividual variation was extremely low with no effects on the analysis. A strong, but imperfect, correspondence was found between ITS clades and amplifiable microsatellite loci. It is concluded that C. membranacea consists of three cryptic species. Using Pacific isolates as an outgroup, the most basal clade included the Central Canary Islands, Cape Verde, and Bonaire (Caribbean) isolates and thus spanned the widest latitude. Two derived sister clades consisted of a southern transtropical group stretching across the SE Caribbean to the Cape Verde Islands and African coast (but not the Canary Islands) and a NE-Canary Island-Mediterranean clade that also included the Red Sea. The detection of overlapping biogeographic distributions highlights the importance of ecotypic differentiation with respect to temperature and the importance of shifting sea surface isotherms that have driven periodic extinctions and recolonizations of the Canary Islands—a crossroads of marine floral exchange—since the last glacial maximum.
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