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Comments on the article, of Olsen et al. (1998): Mediterranean Caulerpa taxifolia and Caulerpa mexicana (Chlorophyta) are not conspecific - Reply
No full textEVIDENCE FOR INDEPENDENT ACQUISITION OF GROUP-I INTRONS IN GREEN-ALGAE
No full textWe report the occurrence of a group I intron, 452 nucleotides in length, in the nuclear small-subunit ribosomal gene of the benthic seaweed Urospora penicilliformis, a member of the green algal class Ulvophyceae. Group I introns have been reported in fungi, myxomycetes, the ciliate genus Tetrahymena, and recently in five unicellular chlorophycean algae. The sequence of the conserved core of the U. penicilliformis group I intron was aligned with that of 15 other introns of this type, and the evolutionary relationships among these introns were examined. Comparison of the ''intron'' tree with phylogenetic hypotheses of the intron-harboring organisms shows that nuclear group I introns in green algae have arisen several times and are not lineage specific
NUCLEAR TRANSFER IN TIER CELLS OF BOSTRYCHIA-RADICANS (RHODOMELACEAE, RHODOPHYTA)
No full textIn the male gametophytes of the marine alga Bostrychia radicans (Montagne) Montagne (Rhodomelaceae, Rhodophyta), axial cells and the initial pericentral cells are uninucleate (4C DNA value). Each pericentral cell of axial segment 5 cuts off a uninucleate (2C) tier cell from the upper surface. In axial segment 7, the 2C nucleus of the lower tier cell divides after DNA synthesis, and a conjunctor cell is formed that fuses with the upper tier cell of the lower adjacent axial segment, transferring a 2C planetic nucleus and producing a secondary pit connection. This upper tier cell contains a single 2C planetic nucleus and one 2C resident nucleus. The nucleus of the lower tier cell remains 2C. Thus a 2-1-2-1 nuclear sequence is evident in tier cells of the upper axis. At axial segment 25, the two 2C nuclei of the upper tier cell become 4C and divide to form four 2C nuclei. One is transmitted to a conjunctor cell that fuses with the lower tier cell establishing a secondary pit connection vertically between the two tier cells of this segment. The lower tier cell contains two 2C nuclei and the upper tier cell has three 2C nuclei. Thus the axial mid-region exhibits a 2-1-2-1 pit-connection sequence and a 3-2-3-2 nuclear sequence in the vertical tier cell series. At axial segment 40, both 2C nuclei of the lower tier cell become 4C and divide into four 2C nuclei. One of these is transmitted by the conjunctor cell to the upper tier cell of the next lower axial segment, thus establishing a second secondary pit connection between the lower tier cell of one axial segment and the upper tier cell of the next lower segment and resulting in a 4-3-4-3 nuclear sequence in the tier-cell series. Occasionally, anomalous 3-1 or 2-2 nuclear sequences develop below axial segment 10
Genetic variation within and among North Atlantic and Baltic populations of the benthic alga Phycodrys rubens (Rhodophyta)
No full textGenetic variation was examined within and among North Atlantic, North Sea and Baltic populations of the benthic red alga Phycodrys rubens using allozymes and random amplified polymorphic DNA (RAPD) markers. On western and eastern North Atlantic coasts distinct allozyme types were found, with the exception of western Newfoundland where East and West Atlantic types co-occur. Along the European coasts, two genetic groups were distinguished by fixed allelic differences: an outer oceanic group and a North Sea/Baltic group. The two genetic types co-occur in the Skagerrak and Kattegat region. Reproductive isolation between the two types is suggested by the lack of hybrids in the overlap zones, and they may therefore represent sibling species. Unexpectedly an analysis of RAPD variation was unable to recover the two cryptic species identified using allozymes. Within-population RAPD variation was similar to or greater than between-population variation. The lack of structure in the RAPD data cannot be attributed solely to technical artefacts of the method but appears to reflect real biological variability. Within-population genomic polymorphisms caused by frequent mutational events are discussed, as are high amounts of genetic drift and possible disruptive selection brought about by stressed habitats. Finally, Baltic and extra-Baltic salinity ecotypes are known to exist in P, rubens. However, no correlation between ecotypic variation and allozyme groups was detected
Genetic divergence correlates with morphological and ecological subdivision in the deep-water elk kelp, Pelagophycus porra (phaeophyceae)
No full textPelagophycus porra (Leman) Setchell has a narrow distribution confined to deep water from the Channel Islands off the southern California coast to central Baja California, Mexico. Distinct morphotypes are consistently correlated with distinctive habitats, that is, windward exposures characterized by strong water motion and rocky substrates, and sheltered areas with soft substrates found on the lee sides of the islands. We tested the hypothesis that morphologically and ecologically distinct forms reflect genetically distinct stands. Individuals representing populations from three islands and the mainland were compared using RFLP analyses of the nuclear rDNA internal transcribed spacers (ITS1 and ITS2), chloroplast trnL (UAA) intron sequences, and random amplified polymorphic DNA (RAPDs). No variation was found in a survey of 20 restriction sites of ITS1 (ca. 320 base pair [bp]) and ITS2 (ca. 360 bp) among individuals from six populations. Likewise, comparisons of trnL intron (241 bp) sequences among nine individuals from seven populations were identical with the exception of a CATAGT insert in two adjacent stands. A RAPD analysis of 24 individuals from nine populations (4 windward and 5 leeward) using 16 primers generated 166 bands. Thirty-eight percent of the bands did not vary, 16% were unique to a given individual, and 46% were variable. Neighbor joining analysis produced a well-resolved tree with moderately high bootstrap support in which windward and leeward populations were easily distinguished. The lack of divergence in both the fast evolving nuclear rDNA-ITS and the chloroplast trnL intron does not support the morphotypes as different species. However, the compartmentalized differentiation shown in the RAPD data clearly points to isolation. This, and previous ecological studies that demonstrate habitat specificity suggest that leeward stands probably comprise a species in situ nascendi
Size and estimated age of genets in eelgrass, Zostera marina, assessed with microsatellite markers
No full textWe examined the spatial distribution of genotypes in a perennial population of eelgrass, Zostera marina L., at two spatial scales. We mapped and sampled 80 ramets in a subtidal area of 20 x 80 m, and an additional 15 ramets in two 1-m(2) sub-quadrats. Ramets were genotyped for seven polymorphic microsatellite loci. Among a total number of 54 genotypes detected, 12 occurred more than once. The ramets of ten of these genotypes occurred in clusters and represented genets based on their expected multi-locus genotype frequencies. The size distribution of genets was uneven with estimated ramet numbers ranging from 2 to 5000. Whereas some areas displayed a high genet diversity, which may indicate past disturbances, large genets (greater than or equal to 10 m(2)) predominated in other locations of the sampled plot. Spatial heterogeneity in clone distribution was also obvious at the smaller sampling scale (15 ramets sam.. pled within m(2)) were the clonal diversity (genets identified/ramets sampled) was 0.24 in one quadrat, and 0.077 in the ether. Ramets belonging to the largest clone were maximally 17 In apart, which corresponds to a genet age of 67 yr based on annual rhizome growth rates. We conclude that the spatial arrangement of clones in seagrasses allows inferences about the past demography and the disturbance regime at a given site which may prove useful for coastal zone management of ecologically valuable seagrass meadows
An Expressed Sequence Tag Analysis of the Intertidal Brown Seaweeds Fucus serratus (L.) and F. vesiculosus (L.) (Heterokontophyta, Phaeophyceae) in Response to Abiotic Stressors
Get PDFPearson GA, Hoarau G, Lago-Leston A, et al. An Expressed Sequence Tag Analysis of the Intertidal Brown Seaweeds Fucus serratus (L.) and F. vesiculosus (L.) (Heterokontophyta, Phaeophyceae) in Response to Abiotic Stressors. Marine Biotechnology. 2009;12(2):195-213.In order to aid gene discovery and uncover genes responding to abiotic stressors in stress-tolerant brown algae of the genus Fucus, expressed sequence tags (ESTs) were studied in two species, Fucus serratus and Fucus vesiculosus. Clustering of over 12,000 ESTs from three libraries for heat shock/recovery and desiccation/rehydration resulted in identification of 2,503, 1,290, and 2,409 unigenes from heat-shocked F. serratus, desiccated F. serratus, and desiccated F. vesiculosus, respectively. Low overall annotation rates (18–31%) were strongly associated with the presence of long 3' untranslated regions in Fucus transcripts, as shown by analyses of predicted protein-coding sequence in annotated and nonannotated tentative consensus sequences. Posttranslational modification genes were overrepresented in the heat shock/recovery library, including many chaperones, the most abundant of which were a family of small heat shock protein transcripts, Hsp90 and Hsp70 members. Transcripts of LI818-like light-harvesting genes implicated in photoprotection were also expressed during heat shock in high light. The expression of several heat-shock-responsive genes was confirmed by quantitative reverse transcription polymerase chain reaction. However, candidate genes were notably absent from both desiccation/rehydration libraries, while the responses of the two species to desiccation were divergent, perhaps reflecting the species-specific physiological differences in stress tolerance previously established. Desiccation-tolerant F. vesiculosus overexpressed at least 17 ribosomal protein genes and two ubiquitinribosomal protein fusion genes, suggesting that ribosome function and/or biogenesis are important during cycles of rapid desiccation and rehydration in the intertidal zone and possibly indicate parallels with other poikilohydric organ organisms such as desiccation-tolerant bryophytes
Phylogenetic relationships within the Sphacelariales (Phaeophyceae): rbcL, RUBISCO spacer and morphology
No full textPhylogenetic 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
Multiple trans-Arctic passages in the red alga Phycodrys rubens: evidence from nuclear rDNA ITS sequences
No full textIn order to investigate how episodes of geological and climatic change have influenced the distribution and evolutionary diversification of Arctic to cold temperate-North Atlantic seaweed species, intraspecific genetic variation was analyzed among isolates of the sublittoral, benthic red alga Phycodrys rubens (collected between June 1992 and January 1994). Rooted phylogenetic analyses of nuclear ribosomal DNA internal transcribed spacer (ITS) sequences and the plastid encoded Rubisco spacer sequences suggest that P. rubens invaded the North Atlantic from the Pacific shortly after the opening of the Bering Strait (3 to 3.5 million years ago), colonizing both the western and eastern Atlantic coasts. Based on these data we further hypothesize that P. rubens survived along the European coasts during the more recent Pleistocene glaciations, while becoming locally extinct along the North American Atlantic coasts. Following retraction of the last ice sheet, the western Atlantic coast was colonized a second time from the Pacific. The presence of two distinct genetic types (based on ITS and Rubisco sequences) along the European coasts is postulated to be a result of isolation and subsequent differentiation. This is likely because ice-free areas are known to have existed in northern Scotland and Norway during the last glaciation. The presence of an East Atlantic genetic type along the West Atlantic coast is believed to be a recent introduction (caused by human activity) of P. rubens to Newfoundland
SCDNA-DNA HYBRIDIZATION STUDIES IN PACIFIC AND CARIBBEAN ISOLATES OF DICTYOSPHAERIA-CAVERNOSA (CHLOROPHYTA) INDICATE A LONG DIVERGENCE
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