Genus Dictyota Research Articles

SPECIES DELIMITATION, TAXONOMY, AND BIOGEOGRAPHY OF DICTYOTA IN EUROPE (DICTYOTALES, PHAEOPHYCEAE)1

Taxonomy of the brown algal genus Dictyota has a long and troubled history. Our inability to distinguish morphological plasticity from fixed diagnostic traits that separate the various species has severely confounded species delineation. From continental Europe, more than 60 species and intraspecific taxa have been described over the last two centuries. Using a molecular approach, we addressed the diversity of the genus in European waters and made necessary taxonomic changes. A densely sampled DNA data set demonstrated the presence of six evolutionarily significant units (ESUs): Dictyota dichotoma (Huds.) J. V. Lamour., D. fasciola (Roth) J. V. Lamour., D. implexa J. V. Lamour., D. mediterranea (Schiffn.) G. Furnari, D. spiralis Mont., and the newly described D. cyanoloma sp. nov., which was previously reported as D. ciliolata from the Mediterranean Sea. Species distributions, based on DNA‐confirmed occurrence records, indicate that all species are geographically confined to the NE Atlantic Ocean with the exception of D. dichotoma and D. implexa, which also occur in South Africa and Bermuda, respectively. To investigate potential hybridization between D. dichotoma and D. implexa, which were previously shown to be sexually compatible in culture, we compiled and analyzed sets of mitochondrial, plastid, and nuclear markers to detect putative hybrids or introgression in natural populations. Failure to detect natural hybrids indicates that effective pre‐ and postzygotic isolation mechanisms are at play in natural populations and supports the by‐product hypothesis of reproductive isolation.

Modelling the dynamics of coral reef macroalgae using a Bayesian belief network approach

Macroalgae are a major benthic component of coral reefs and their dynamics influence the resilience of coral reefs to disturbance. However, the relative importance of physical and ecological processes in driving macroalgal dynamics is poorly understood. Here we develop a Bayesian belief network (BBN) model to integrate many of these processes and predict the growth of coral reef macroalgae. Bayesian belief networks use probabilistic relationships rather than deterministic rules to quantify the cause and effect assumptions. The model was developed using both new empirical data and quantified relationships elicited from previous studies. We demonstrate the efficacy of the BBN to predict the dynamics of a common Caribbean macroalgal genus Dictyota. Predictions of the model have an average accuracy of 55% (implying that 55% of the predicted categories of Dictyota cover were assigned to the correct class). Sensitivity analysis suggested that macroalgal dynamics were primarily driven by top–down processes of grazing rather than bottom–up nutrification. BBNs provide a useful framework for modelling complex systems, identifying gaps in our scientific understanding and communicating the complexities of the associated uncertainties in an explicit manner to stakeholders. We anticipate that accuracies will improve as new data are added to the model.

De Clerck, O.2003. The genus Dictyota (Dictyotales, Phaeophyta) in the Indian Ocean.

Nordic Journal of BotanyVolume 23, Issue 3 p. 344-344 De Clerck, O.2003. The genus Dictyota (Dictyotales, Phaeophyta) in the Indian Ocean. Poul Møller Pedersen, Poul Møller PedersenSearch for more papers by this author Poul Møller Pedersen, Poul Møller PedersenSearch for more papers by this author First published: 28 June 2008 https://doi.org/10.1111/j.1756-1051.2003.tb00403.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume23, Issue3July 2003Pages 344-344 RelatedInformation

GEOGRAPHIC AND GENETIC VARIATION IN FEEDING PREFERENCE FOR CHEMICALLY DEFENDED SEAWEEDS

Genetic variation in tolerance for seaweed chemical defenses among populations of marine herbivores is poorly described, either because few marine studies have addressed the issue or because the feeding preferences of populations of marine herbivores rarely differentiate. We address this using the polyphagous amphipod Ampithoe longimana (Crustacea), which commonly consumes, and lives on, terpene-rich brown seaweeds in the tropical genus Dictyota. Previous work demonstrated that in areas where the amphipod and seaweeds overlap geographically, these chemically deterrent seaweeds provide the amphipod with spatial refuges from predation by omnivorous fishes that avoid consuming Dictyota. However, the amphipod's distribution extends northward of the seaweed's distribution, making this benefit of association unavailable to more northerly populations of amphipods. On average, populations sympatric with Dictyota have stronger feeding preference for Dictyota species and greater fitness when raised on Dictyota than do populations that are outside Dictyota's geographic endpoint. These results are consistent with the hypothesis that in areas where the amphipods co-exist with Dictyota, selection favors amphipods that tolerate Dictyota's chemical defenses and thereby access its enemy-free space. Amphipods allopatric with Dictyota are unable to tolerate Dictyota's chemical defenses, either because of selection, drift, or some mix of both forces. A trade-off between preference for Dictyota and for the chemically distinct seaweed Hypnea musciformis is suggested by the finding that populations with high preference for Dictyota tended to have lower preference for Hypnea. However, this population-level pattern appears to be the result of independent evolution and not a genetic trade-off: an analysis of full-sib families within a single population detected heritable variation in preferences for Dictyota and suggested this for Hypnea (although the latter was not statistically significant), yet no family-level covariation was detected. Phylogeographic analysis of mitocondrial DNA and nuclear sequences indicates a strong historical break between populations sympatric with Dictyota and populations more than 500 km beyond Dictyota's geographic endpoint. The historical separation of these most northerly populations could have allowed a random accumulation of alleles to effectively degrade tolerance for Dictyota, although selection may also be responsible for the degradation.

GEOGRAPHIC VARIATION AMONG HERBIVORE POPULATIONS IN TOLERANCE FOR A CHEMICALLY RICH SEAWEED

Previous investigations have shown that the sedentary amphipod Ampithoe longimana escapes consumers by selectively living on and eating chemically defended seaweeds in the genus Dictyota. However, A. longimana and Dictyota overlap only in the southern portion of the amphipod's range; Dictyota is not available to amphipods from more northerly regions. We used this disjunction in distribution to test the hypothesis that A. longimana populations co-occurring with Dictyota would have greater tolerance for the seaweed's chemical defenses and would display higher feeding preference for, and fitness on, the seaweed than would more northerly populations. We also evaluated the genetic vs. phenotypic basis of these patterns and attempted to detect trade-offs between tolerance for Dictyota and ability to use other plants as foods. Such geographic studies of herbivory have been conducted using terrestrial insects, but few studies have focused on other herbivores, and this is especially true for marine systems. In multiple-choice feeding assays with both field-collected and laboratory-reared adults, a North Carolina population of A. longimana sympatric with Dictyota more readily fed on Dictyota and was more resistant to Dictyota's deterrent chemistry than was a Connecticut population from outside of Dictyota's geographic range. When raised on Dictyota menstrualis and D. ciliolata, A. longimana juveniles from North Carolina grew faster, matured faster, and produced more reproductive females than did Connecticut juveniles. The differential tolerance for Dictyota has a genetic basis, as it was maintained through two generations grown to maturity in a common environment. When several northern and southern populations were assayed, they displayed similar regional differences in feeding preferences. Though southern juveniles had higher fitness on Dictyota than northern juveniles, southern juveniles performed as well as northern juveniles when raised on seven other seaweeds, including seaweeds (e.g., Fucus vesiculosus and Sargassum filipendula) that produce secondary metabolites in a different class from those found in Dictyota. Thus, tolerating Dictyota did not incur detectable performance trade-offs when juveniles were confined to feeding on alternative seaweeds. Our results suggest that the evolution of host preferences may depend more on the host value as a refuge from enemies than on minimizing the costs of tolerating plant secondary metabolites.

Effect of algal architecture on associated fauna: some evidence from phytal molluscs

In the southern Mediterranean Sea, replicate samples of six common upper-infralittoral algae (Cystoseira barbatula, Cystoseira spinosa, Sargassum vulgare, Halopteris scoparia, Dictyota fasciola, and Dictyota dichotoma) were collected with the major goal of investigating the composition and structure of molluscan assemblages between the algal species. In order to measure the habitat architecture of the six algal species and relate this to the molluscan assemblages, several structural attributes were calculated on each individual plant. There were differences in architectural attributes between the six algal species, with data recorded for S. vulgare and H. scoparia more similar to data for C. barbatula and C. spinosa (which grouped closely), than for the two species belonging to the genus Dictyota, which had a less complex structure. A total of 1,914 specimens and 57 species of molluscs were found on the collected algae. The abundance and diversity of the molluscan assemblages were significantly different between different macroalgae. In general S. vulgare, C. barbatula and C. spinosa supported a higher abundance, greater number of species, Shannon–Wiener diversity, and Margalef's index than the remaining three algal species. Both multivariate analyses (i.e. cluster and multidimensional scaling) and a posteriori tests (Student–Neuman–Keuls' test) demonstrated that samples collected on D. dichotoma were well separated, reflecting the lowest values of abundance and diversity. The molluscan assemblage data were also correlated to the attributes of algal architecture revealing that the combination of degree of branching, algal width and the log of the stem width provides a good explanation for molluscan structure. Differences in the molluscan assemblages of these six common Mediterranean algae can be attributed to different algal architectures, and, consequently, these could be related to the supposed variations in food availability and predation rate.

Molecular Systematics in the Genus Dictyota (Dictyotales, Phaeophyta): A First Attempt Based on Restriction Patterns of the Internal Transcribed Spacer 1 of the rDNA (ARDRA-ITS1)

Molecular Systematics in the Genus Dictyota (Dictyotales, Phaeophyta): A First Attempt Based on Restriction Patterns of the Internal Transcribed Spacer 1 of the rDNA (ARDRA-ITS1)

Marine brown algae (Phaeophyta) from the north coast of Papua New Guinea, with a description of Dictyota magneana sp. nov.

The marine benthic brown algae of the north coast of Papua New Guinea (mainly from Madang province) are documented, based on collections made by the first author, between 1980 and 1990. All records [34 identified taxa (+ Sargassum spp.)] are listed with bibliographic, taxonomic, nomenclatural and biogeographical notes. The specimens belonging to the genus Dictyota are identified according to recent species definitions. D. magneana De Clerck et Coppejans is described as new to science. Only some representatives of the genus Sargassum have been identified to species level. The phaeophycean flora of the north coast is very similar to that of the south coast (Port Moresby area); nevertheless some differences can be observed.

Notes on Dictyota vieillardii and D. adnata (Dictyotaceae, Phaeophyta)

SummaryDe Clerck, O. & Coppejans, E.: Notes on Dictyota vieillardii and D. adnata (Dictyotaceae, Phaeophyta). – Taxon 46: 33‐36. 1997. – ISSN 0040‐0262.Post considered Dictyota adnata Zanardini to be a synonym of D. vieillardii Kütz. However, examination of the type specimen of D. vieillardii proves it does not belong to the genus Dictyota but represents the Vaughaniella stage of a Padina species. D. vieillardii van filiformis Kütz. is also shown to represent a Vaughaniella stage. The type specimen of D. adnata could not be traced and the designation of a neotype by Coppejans is confirmed.

Uncommon 16:1 (n-5) acid from Dictyota dichotoma and fatty acids of some brown algae of Dictyotaceae

The detailed fatty acid composition of the brown algae, Dictyota dichotoma, Dictyopteris divaricata and Dictyota cervicornis are reported. About 35 fatty acids were identified, of which 16:0, 18:4 (n-3), 18:1(n-9), 14:0 and 20:4(n-6) predominated in each sample. A high content of an uncommon 16:1(n-5) and the occurrence of C 22 polyunsaturated fatty acids in minute amounts are characteristic features of algae from the genus Dictyota and Dictyopteris divaricata. The structure of 16:1(n-5) was confirmed by GC and mass spectrometry of its derivatives. The distribution of fatty acids among the polar lipids of Dictyota dichotoma are reported. The 16:1(n-5) acid was identified in glycolipids and betaine lipid.

A diterpene epoxide from the marine brown alga Dictyota sp.: Possible vasopressin V1 receptor antagonist

A novel epoxide, in addition to eight known diterpenes, has been isolated from a marine brown alga of the genus Dictyota. The structures of these compounds were established by the interpretation and comparison of spectral data with literature data. Most of the isolates demonstrated vasopressin receptor antagonist activity in vitro with the new epoxide being the most active of the diterpenes tested.

Prey nutritional quality and the effectiveness of chemical defenses against tropical reef fishes.

Many coral-reef seaweeds and sessile invertebrates produce both secondary chemicals and mineral or fibrous skeletal materials that can reduce their susceptibility to consumers. Although skeletal materials often have been assumed to function as physical defenses, their deterrent effectiveness may derive from their reduction of prey nutritional quality as well as from noxiousness of the skeletal material itself. To test the relative importance of prey nutritional quality and chemical defenses in susceptibility to predation, we offered reef fishes on Guam a choice of artificial foods varying in nutritional quality (4% versus 22% protein) and in secondary chemistry (spanning approximately natural concentration ranges). Field feeding assays were performed with pachydictyol A from the pantropical brown seaweed genus Dictyota, manoalide from the Micronesian sponge Luffariella variabilis, and a brominated diphenyl ether from the Micronesian sponge Dysidea sp. The results indicated that chemical defenses were less effective in high- than in low-quality foods. In paired assays with metabolite-free controls, all three compounds at natural concentrations significantly reduced feeding by reef fishes only in assays using low-quality food, and not in assays with high-quality food. When fishes were offered an array of artificial foods varying in both food quality and metabolite concentration, food quality significantly affected fish feeding in all three cases, while secondary chemistry was significant in only one. Thus differences in nutritional quality, within the natural range among reef organisms, can be comparable to or greater in importance than secondary chemistry in affecting feeding preferences of their consumers. Reduced nutritional quality may be an important selective advantage of producing indigestible structural materials, in addition to their roles as physical support and defense, in coral reef organisms.

Chemosystematic and biogeographic studies of the diterpenes from the marine brown alga Dictyota dichotoma

Dictyota dichotoma is claimed to be the only cosmopolitan species of the genus Dictyota. It is also the species that has been the most extensively studied by phytochemists, yielding a plethora of diterpenes as major secondary metabolites. The question whether D. dichotoma is a true cosmopolitan species of defined limits is examined in this work. Diterpenes isolated from several populations, collected all over the world, are used as a criterion. The dissimilarity between diterpene compositions and mainly the important differences observed for the taxonomic indices suggested that D. dichotoma is actually a complex of species. The cosmopolitan character of its geographic distribution should be revised.

A chemotaxonomic study of diterpenes from marine brown algae of the genus Dictyota

Diterpenes from Dictyota species appear to be valuable taxonomic markers and showed, for various species, strong correlation with botanic data. Our results corroborate the Theory of Micromolecular Evolution that states that higher oxidation levels, in a given taxon, are characteristic of evolutionarily more advanced components.

Three further dolabellane diterpenoids from Dictyota sp.

A brown alga of the genus Dictyota has yielded three new dolabellane diterpenoids the structures of which were elucidated mainly by spectroscopic methods.