Molecular systematics, historical ecology, and phylogeography of <i>Halimeda</i> (Bryopsidales)

Halimeda (Bryopsidales), a genus of calcified, segmented green seaweeds, abounds in reefs and lagoons throughout the tropics. To investigate phylogenetic, phylogeographic, and historic ecological relationships of the genus, the nuclear rDNA including the SSU and both ITS regions were sequenced. A maximum likelihood tree revealed the following: (1) there were anatomical and morphological synapomorphies for five well-supported lineages; (2) the last common ancestor of one lineage invaded sandy substrata; those of two other lineages established in wave-affected habitats, whereas the cenancestor of the remaining two lineages occupied sheltered rocky slopes. Yet, several species adapted to new habitats subsequently, resulting in several cases of convergence; (3) all lineages separated into Atlantic and Indo-Pacific daughters, likely resulting from the rise of the Panamanian Isthmus. Each daughter pair gave rise to additional convergent species in similar habitats in different oceans; (4) Halimeda opuntia, the only monophyletic pantropical species detected so far, dispersed from the Indo-Pacific into the Atlantic well after the closure event; (5) minor SSU-sequence differences across species and phylogeographic patterns of vicariance indicated a relatively recent diversification of the extant diversity. Cretaceous and Early Tertiary fossil look-alikes of modern species must then have resulted from iterative convergence

Macroecology meets macroevolution: evolutionary niche dynamics in the seaweed <i>Halimeda</i>

Aim Because of their broad distribution in geographical and ecological dimensions, seaweeds (marine macroalgae) offer great potential as models for marine biogeographical inquiry and exploration of the interface between macroecology and macroevolution. This study aims to characterize evolutionary niche dynamics in the common green seaweed genus Halimeda, use the observed insights to gain understanding of the biogeographical history of the genus and predict habitats that can be targeted for the discovery of species of special biogeographical interest.Location Tropical and subtropical coastal waters.Methods The evolutionary history of the genus is characterized using molecular phylogenetics and relaxed molecular clock analysis. Niche modelling is carried out with maximum entropy techniques and uses macroecological data derived from global satellite imagery. Evolutionary niche dynamics are inferred through application of ancestral character state estimation.Results A nearly comprehensive molecular phylogeny of the genus was inferred from a six-locus dataset. Macroecological niche models showed that species distribution ranges are considerably smaller than their potential ranges. We show strong phylogenetic signal in various macroecological niche features.Main conclusions The evolution of Halimeda is characterized by conservatism for tropical, nutrient-depleted habitats, yet one section of the genus managed to invade colder habitats multiple times independently. Niche models indicate that the restricted geographical ranges of Halimeda species are not due to habitat unsuitability, strengthening the case for dispersal limitation. Niche models identified hotspots of habitat suitability of Caribbean species in the eastern Pacific Ocean. We propose that these hotspots be targeted for discovery of new species separated from their Caribbean siblings since the Pliocene rise of the Central American Isthmus

Distribution, occurrence and biotoxin composition of the main

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Morphological characterization of lineages within the calcified tropical seaweed genus <i>Halimeda</i> (Bryopsidales, Chlorophyta)

Halimeda Lamouroux constitutes a genus of calcified and segmented green seaweeds within the Bryopsidales. Molecular phylogenetic assessments have uncovered five principal monophyletic lineages within the genus. In the present study we define these lineages morphologically. We gathered morphological data from specimens used in the molecular analyses as well as from collections having a similar morphology and originating from the same geographical region. Starting from the lineages and their morphological synapomorphies, we define and illustrate five natural sections within Halimeda. All or most medullary siphons traversing the nodes between segments fuse into a single unit in specimens of lineage 1 (section Rhipsalis), and segments at the thallus base fuse with one another. Medullary siphons of specimens in lineage 2 (section Micronesicae) traverse the node without fusing. Medullary siphons of specimens in lineage 3 (section Halimeda) divide frequently below the nodes and become entangled among one another. The segments of specimens in this lineage possess a continuous uncorticated band along the distal perimeter instead of three or more pits as encountered in segments of specimens in all other lineages. Members of lineage 4 (section Pseudo-opuntia) possess club-shaped subperipheral utricles in their cortical region. Medullary siphons of specimens in lineage 5 (section Opuntia) fuse over only a short distance at the nodes and retain their identity. Apart from these synapomorphies, the lineages can be delimited further by a characteristic combination of symplesiomorphies and homoplasies. In addition we examined the morphology of H. bikinensis Taylor, a species not included in the molecular analyses, and discuss its ambiguous position in our sectional system

A METHOD FOR OBTAINING AXENIC ALGAL CULTURES USING THE ANTIBIOTIC CEFOTAXIME WITH EMPHASIS ON CLADOPHOROPSIS-MEMBRANACEA (CHLOROPHYTA)

Axenic cultures of the tropical green seaweed Cladophoropsis membranacea (C. Agardh) Boergesen were obtained by cutting 2-mm apical tips from fast-growing unialgal filaments and incubating them in 1/2PES containing 100-mu-g.mL-1 cefotaxime. After 1 week, apical tips were cut from the newly grown plantlets, washed through a series of sterile drops of seawater, and incubated in sterile 1/2PES. Plantlets were screened for the presence of bacteria by incubating droplets of the culture medium on peptone agar plates and by examining DAPI-stained filaments. Ninety to one hundred percent of the plantlets obtained with this treatment were axenic. Cefotaxime was also effective against cyanobacteria but of only limited value in rhodophytes

Molecular phylogeny and morphology of the marine diatom Talaroneis posidoniae gen. et sp. nov. (Bacillariophyta) advocate the return of the Plagiogrammaceae to the pennate diatoms

A new genus, Talaroneis Kooistra & De Stefano, gen. nov. and a new species T. posidoniae Kooistra & De Stefano, sp. nov. are described. The elongate cells, which were found on a leaf of Posidonia oceanica, formed star-, zigzag- or ribbon-shaped colonies in culture. The distinctive character of T. posidoniae was the presence of two silica wings flanking a furrow near each apical pore field. Uniseriate, transverse striae were arranged perpendicular to the apical axis; those on one side of the valve offset with respect to those on the other side. Valve poroids were occluded by perforated rotae. These morphological characteristics placed the taxon unambiguously within the supposedly centric family Plagiogrammaceae. The taxon would be excluded from the morphologically similar araphid family Rhaphoneidaceae because it lacked apical labiate processes and a clearly defined sternum. Nonetheless, a phylogeny inferred from nuclear-encoded SSU ribosomal DNA sequences of a range of diatoms unambiguously recovered T. posidoniae within the araphid pennates, close to Rhaphoneis cf. belgica (Rhaphoneidaceae). Apparently, labiate processes were lost secondarily in T. posidoniae and possibly in the common ancestor of all Plagiogrammaceae. Valve ultrastructural features of T. posidoniae would allow placement of the new species in Dimeregrammopsis but this genus was invalidly described. We transferred the single species of this genus to T. furcigerum (Grunow) Sterrenburg, comb. nov. and designated it as the type species of Talaroneis

Molecular and morphometric data pinpoint species boundaries in <i>Halimeda</i> section <i>Rhipsalis</i> (Bryopsidales, Chlorophyta)

Molecular systematic studies have changed the face of algal taxonomy. Particularly at the species level, molecular phylogenetic research has revealed the inaccuracy of morphology-based taxonomy: Cryptic and pseudo-cryptic species were shown to exist within many morphologically conceived species. This study focused on section Rhipsalis of the green algal genus Halimeda. This section was known to contain cryptic diversity and to comprise species with overlapping morphological boundaries. In the present study, species diversity within the section and identity of individual specimens were assessed using ITS1–5.8S–ITS2 (nrDNA) and rps3 (cpDNA) sequence data. The sequences grouped in a number of clear-cut genotypic clusters that were considered species. The same specimens were subjected to morphometric analysis of external morphological and anatomical structures. Morphological differences between the genotypic cluster species were assessed using discriminant analysis. It was shown that significant morphological differences exist between genetically delineated species and that allocation of specimens to species on the basis of morphometric variables is nearly perfect. Anatomical characters yielded better results than external morphological characters. Two approaches were offered to allow future morphological identifications: a probabilistic approach based on classification functions of discriminant analyses and the classical approach of an identification key

Phylogenetic position of Toxarium, a pennate-like lineage within centric diatoms (Bacillariophyceae)

The diatom genus Toxarium Bailey has been treated as a pennate because of its elongate shape and benthic lifestyle (it grows attached to solid substrata in the marine sublittoral). Yet its valve face lacks all structures that would ally it with the pennates, such as apical labiate processes, a midrib (sternum) subtending secondary ribs and rows of pores extending perpendicularly out from the mid-rib, or a raphe system. Instead, pores are scattered irregularly over the valve face and only form two distinct rows along the perimeter of the valve face. In our nuclear small subunit rDNA phylogenies, Toxarium groups with bi- and multipolar centrics, as sister to Lampriscus A. Schmidt. Thus, the genus acquired a pennate-like shape and lifestyle independently from that of the true pennates. The two species known, T. hennedyanum Grunow and T. undulatum Bailey, differ only in a single feature: the valve perimeter of the former shows only a central expansion, whereas that of the latter possesses in addition a regular undulation. Yet both forms were observed in our monoclonal cultures, indicating that the two taxa represent extremes in a plasticity range. Toxarium resembles another elongate and supposedly araphid diatom, Ardissonea De Notaris, in being motile. Cells can move at speeds of up to 4 μm·s-1 through secretion of mucilage from the cell poles or they remain stationary for longer periods, when they form short polysaccharide stalks. Division during longer periods of quiescence leads to the formation of small colonies of linked or radiating cells