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Jon L. Norenburg - One of the best experts on this subject based on the ideXlab platform.
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A phylum-wide survey reveals multiple independent gains of head regeneration ability in Nemertea
2018Co-Authors: Eduardo E. Zattara, Fernando Ángel Fernández-Álvarez, Terra C. Hiebert, Alexandra E. Bely, Jon L. NorenburgAbstract:Animals vary widely in their ability to regenerate, suggesting that regenerative abilities have a rich evolutionary history. However, our understanding of this history remains limited because regeneration ability has only been evaluated in a tiny fraction of species. Available comparative regeneration studies have identified losses of regenerative ability, yet clear documentation of gains is lacking. We surveyed regenerative ability in 34 species spanning the phylum Nemertea, assessing the ability to regenerate heads and tails either through our own experiments or from literature reports. Our sampling included representatives of the 10 most diverse families and all three orders comprising this phylum. We generated a phylogenetic framework using sequence data to reconstruct the evolutionary history of head and tail regeneration ability across the phylum and found that while all evaluated species can remake a posterior end, surprisingly few could regenerate a complete head. Our analysis reconstructs a Nemertean ancestor unable to regenerate a head and indicates at least four separate lineages have independently gained head regeneration ability, one such gains reconstructed as taking place within the last 10-15 mya. Our study highlights Nemerteans as a valuable group for studying evolution of regeneration and identifying mechanisms associated with repeated gains of regenerative ability.
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The Necessity of DNA Taxonomy to Reveal Cryptic Diversity and Spatial Distribution of Meiofauna, with a Focus on Nemertea
2016Co-Authors: Francesca Leasi, Jon L. NorenburgAbstract:Meiofauna represent one of the most abundant and diverse communities in marine benthic ecosystems. However, an accurate assessment of diversity at the level of species has been and remains challenging for these microscopic organisms. Therefore, for many taxa, especially the soft body forms such as Nemerteans, which often lack clear diagnostic morphological traits, DNA taxonomy is an effective means to assess species diversity. Morphological taxonomy of Nemertea is well documented as complicated by scarcity of unambiguous character states and compromised by diagnoses of a majority of species (and higher clades) being inadequate or based on ambiguous characters and character states. Therefore, recent studies have advocated for the primacy of molecular tools to solve the taxonomy of this group. DNA taxonomy uncovers possible hidden cryptic species, provides a coherent means to systematize taxa in definite clades, and also reveals possible biogeographic patterns. Here, we analyze diversity of Nemertean species by considering the barcode region of the mitochondrial gene Cytochrome Oxidase subunit I (COI) and different species delineation approaches in order to infer evolutionarily significant units. In the aim to uncover actual diversity of meiofaunal Nemerteans across different sites in Central America, COI sequences were obtained for specimens assigned here to the genera Cephalothrix, Ototyphlonemertes, and Tetrastemma-like worms, each commonly encountered in our sampling. Additional genetic, taxonomic, and geographic data of other specimens belonging to these genera were added from GenBank. Results are consistent across different DN
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A Transcriptomic Approach to Ribbon Worm Systematics (Nemertea): Resolving the Pilidiophora Problem
Molecular Biology and Evolution, 2014Co-Authors: Sónia C. S. Andrade, Hiroshi Kajihara, James M. Turbeville, Per Sundberg, Malin Strand, H. Montenegro, Megan L. Schwartz, Jon L. Norenburg, Gonzalo GiribetAbstract:Resolving the deep relationships of ancient animal lineages has proven difficult using standard Sanger-sequencing approaches with a handful of markers. We thus reassess the relatively well-studied phylogeny of the phylum Nemertea (ribbon worms)—for which the targeted gene approaches had resolved many clades but had left key phylogenetic gaps—by using a phylogenomic approach using Illumina-based de novo assembled transcriptomes and automatic orthology prediction methods. The analysis of a concatenated data set of 2,779 genes (411,138 amino acids) with about 78% gene occupancy and a reduced version with 95% gene occupancy, under evolutionary models accounting or not for site-specific amino acid replacement patterns results in a well-supported phylogeny that recovers all major accepted Nemertean clades with the monophyly of HeteroNemertea, HoploNemertea, Monostilifera, being well supported. Significantly, all the ambiguous patterns inferred from Sanger-based approaches were resolved, namely the monophyly of PalaeoNemertea and Pilidiophora. By testing for possible conflict in the analyzed supermatrix, we observed that concatenation was the best solution, and the results of the analyses should settle prior debates on Nemertean phylogeny. The study highlights the importance, feasibility, and completeness of Illumina-based phylogenomic data matrices.
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The necessity of DNA taxonomy to reveal cryptic diversity and spatial distribution of meiofauna, with a focus on Nemertea.
PLoS ONE, 2014Co-Authors: Francesca Leasi, Jon L. NorenburgAbstract:Meiofauna represent one of the most abundant and diverse communities in marine benthic ecosystems. However, an accurate assessment of diversity at the level of species has been and remains challenging for these microscopic organisms. Therefore, for many taxa, especially the soft body forms such as Nemerteans, which often lack clear diagnostic morphological traits, DNA taxonomy is an effective means to assess species diversity. Morphological taxonomy of Nemertea is well documented as complicated by scarcity of unambiguous character states and compromised by diagnoses of a majority of species (and higher clades) being inadequate or based on ambiguous characters and character states. Therefore, recent studies have advocated for the primacy of molecular tools to solve the taxonomy of this group. DNA taxonomy uncovers possible hidden cryptic species, provides a coherent means to systematize taxa in definite clades, and also reveals possible biogeographic patterns. Here, we analyze diversity of Nemertean species by considering the barcode region of the mitochondrial gene Cytochrome Oxidase subunit I (COI) and different species delineation approaches in order to infer evolutionarily significant units. In the aim to uncover actual diversity of meiofaunal Nemerteans across different sites in Central America, COI sequences were obtained for specimens assigned here to the genera Cephalothrix, Ototyphlonemertes, and Tetrastemma-like worms, each commonly encountered in our sampling. Additional genetic, taxonomic, and geographic data of other specimens belonging to these genera were added from GenBank. Results are consistent across different DNA taxonomy approaches, and revealed (i) the presence of several hidden cryptic species and (ii) numerous potential misidentifications due to traditional taxonomy. (iii) We additionally test a possible biogeographic pattern of taxonomic units revealed by this study, and, except for a few cases, the putative species seem not to be widely distributed, in contrast to what traditional taxonomy would suggest for the recognized morphotypes.
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mutation and selection cause codon usage and bias in mitochondrial genomes of ribbon worms Nemertea
PLOS ONE, 2014Co-Authors: Haixia Chen, Jon L. Norenburg, Shichun Sun, Per SundbergAbstract:The phenomenon of codon usage bias is known to exist in many genomes and it is mainly determined by mutation and selection. To understand the patterns of codon usage in Nemertean mitochondrial genomes, we use bioinformatic approaches to analyze the protein-coding sequences of eight Nemertean species. Neutrality analysis did not find a significant correlation between GC12 and GC3. ENc-plot showed a few genes on or close to the expected curve, but the majority of points with low-ENc values are below it. ENc-plot suggested that mutational bias plays a major role in shaping codon usage. The Parity Rule 2 plot (PR2) analysis showed that GC and AT were not used proportionally and we propose that codons containing A or U at third position are used preferentially in Nemertean species, regardless of whether corresponding tRNAs are encoded in the mitochondrial DNA. Context-dependent analysis indicated that the nucleotide at the second codon position slightly affects synonymous codon choices. These results suggested that mutational and selection forces are probably acting to codon usage bias in Nemertean mitochondrial genomes.
Haixia Chen - One of the best experts on this subject based on the ideXlab platform.
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complete mitochondrial genome sequences of two parasitic commensal Nemerteans gononemertes parasita and nemertopsis tetraclitophila Nemertea hoploNemertea
Parasites & Vectors, 2014Co-Authors: Wen-yan Sun, Per Sundberg, Malin Strand, Haixia Chen, Wei Shi, Shichun SunAbstract:Background Most Nemerteans (phylum Nemertea) are free-living, but about 50 species are known to be firmly associated with other marine invertebrates. For example, Gononemertes parasita is associated with ascidians, and Nemertopsis tetraclitophila with barnacles. There are 12 complete or near-complete mitochondrial genome (mitogenome) sequences of Nemerteans available in GenBank, but no mitogenomes of none free-living Nemerteans have been determined so far. In the present paper complete mitogenomes of the above two parasitic/commensal Nemerteans are reported.
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mutation and selection cause codon usage and bias in mitochondrial genomes of ribbon worms Nemertea
PLOS ONE, 2014Co-Authors: Haixia Chen, Jon L. Norenburg, Shichun Sun, Per SundbergAbstract:The phenomenon of codon usage bias is known to exist in many genomes and it is mainly determined by mutation and selection. To understand the patterns of codon usage in Nemertean mitochondrial genomes, we use bioinformatic approaches to analyze the protein-coding sequences of eight Nemertean species. Neutrality analysis did not find a significant correlation between GC12 and GC3. ENc-plot showed a few genes on or close to the expected curve, but the majority of points with low-ENc values are below it. ENc-plot suggested that mutational bias plays a major role in shaping codon usage. The Parity Rule 2 plot (PR2) analysis showed that GC and AT were not used proportionally and we propose that codons containing A or U at third position are used preferentially in Nemertean species, regardless of whether corresponding tRNAs are encoded in the mitochondrial DNA. Context-dependent analysis indicated that the nucleotide at the second codon position slightly affects synonymous codon choices. These results suggested that mutational and selection forces are probably acting to codon usage bias in Nemertean mitochondrial genomes.
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Complete mitochondrial genome sequences of two parasitic/commensal Nemerteans, Gononemertes parasita and Nemertopsis tetraclitophila (Nemertea: HoploNemertea)
Parasites & Vectors, 2014Co-Authors: Wen-yan Sun, Per Sundberg, Malin Strand, Haixia Chen, Wei Shi, Shichun SunAbstract:Background Most Nemerteans (phylum Nemertea) are free-living, but about 50 species are known to be firmly associated with other marine invertebrates. For example, Gononemertes parasita is associated with ascidians, and Nemertopsis tetraclitophila with barnacles. There are 12 complete or near-complete mitochondrial genome (mitogenome) sequences of Nemerteans available in GenBank, but no mitogenomes of none free-living Nemerteans have been determined so far. In the present paper complete mitogenomes of the above two parasitic/commensal Nemerteans are reported.
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a comparative study of Nemertean complete mitochondrial genomes including two new ones for nectonemertes cf mirabilis and zygeupolia rubens may elucidate the fundamental pattern for the phylum Nemertea
BMC Genomics, 2012Co-Authors: Per Sundberg, Haixia Chen, Shichun Sun, Weicheng Ren, Jon L. NorenburgAbstract:The mitochondrial genome is important for studying genome evolution as well as reconstructing the phylogeny of organisms. Complete mitochondrial genome sequences have been reported for more than 2200 metazoans, mainly vertebrates and arthropods. To date, from a total of about 1275 described Nemertean species, only three complete and two partial mitochondrial DNA sequences from Nemerteans have been published. Here, we report the entire mitochondrial genomes for two more Nemertean species: Nectonemertes cf. mirabilis and Zygeupolia rubens. The sizes of the entire mitochondrial genomes are 15365 bp for N. cf. mirabilis and 15513 bp for Z. rubens. Each circular genome contains 37 genes and an AT-rich non-coding region, and overall nucleotide composition is AT-rich. In both species, there is significant strand asymmetry in the distribution of nucleotides, with the coding strand being richer in T than A and in G than C. The AT-rich non-coding regions of the two genomes have some repeat sequences and stem-loop structures, both of which may be associated with the initiation of replication or transcription. The 22 tRNAs show variable substitution patterns in Nemerteans, with higher sequence conservation in genes located on the H strand. Gene arrangement of N. cf. mirabilis is identical to that of Paranemertes cf. peregrina, both of which are HoploNemertea, while that of Z. rubens is the same as in Lineus viridis, both of which are HeteroNemertea. Comparison of the gene arrangements and phylogenomic analysis based on concatenated nucleotide sequences of the 12 mitochondrial protein-coding genes revealed that species with closer relationships share more identical gene blocks. The two new mitochondrial genomes share many features, including gene contents, with other known Nemertean mitochondrial genomes. The tRNA families display a composite substitution pathway. Gene order comparison to the proposed ground pattern of Bilateria and some lophotrochozoans suggests that the Nemertean ancestral mitochondrial gene order most closely resembles the heteroNemertean type. Phylogenetic analysis proposes a sister-group relationship between Hetero- and HoploNemertea, which supports one of two recent alternative hypotheses of Nemertean phylogeny.
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disentangling ribbon worm relationships multi locus analysis supports traditional classification of the phylum Nemertea
Cladistics, 2012Co-Authors: Sónia C. S. Andrade, Hiroshi Kajihara, Jörn Von Döhren, Malin Strand, Megan L. Schwartz, Juan Junoy, Haixia Chen, Shichun Sun, Martin Thiel, Jon L. NorenburgAbstract:The phylogenetic relationships of selected members of the phylum Nemertea are explored by means of six markers amplified from the genomic DNA of freshly collected specimens (the nuclear 18S rRNA and 28S rRNA genes, histones H3 and H4, and the mitochondrial genes 16S rRNA and cytochrome c oxidase subunit I). These include all previous markers and regions used in earlier phylogenetic analyses of Nemerteans, therefore acting as a scaffold to which one could pinpoint any previously published study. Our results, based on analyses of static and dynamic homology concepts under probabilistic and parsimony frameworks, agree in the non-monophyly of PalaeoNemertea and in the monophyly of Heteronemerta and HoploNemertea. The position of Hubrechtella and the Pilidiophora hypothesis are, however, sensitive to analytical method, as is the monophyly of the non-hubrechtiid palaeoNemerteans. Our results are, however, consistent with the main division of HoploNemertea into Polystilifera and Monostilifera, the last named being divided into CrateNemertea and DistromatoNemertea, as well as into the main division of HeteroNemertea into Baseodiscus and the remaining species. The study also continues to highlight the deficient taxonomy at the family and generic level within Nemertea and sheds light on the areas of the tree that require further refinement. � The Willi Hennig Society 2011.
Hiroshi Kajihara - One of the best experts on this subject based on the ideXlab platform.
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A Transcriptomic Approach to Ribbon Worm Systematics (Nemertea): Resolving the Pilidiophora Problem
Molecular Biology and Evolution, 2014Co-Authors: Sónia C. S. Andrade, Hiroshi Kajihara, James M. Turbeville, Per Sundberg, Malin Strand, H. Montenegro, Megan L. Schwartz, Jon L. Norenburg, Gonzalo GiribetAbstract:Resolving the deep relationships of ancient animal lineages has proven difficult using standard Sanger-sequencing approaches with a handful of markers. We thus reassess the relatively well-studied phylogeny of the phylum Nemertea (ribbon worms)—for which the targeted gene approaches had resolved many clades but had left key phylogenetic gaps—by using a phylogenomic approach using Illumina-based de novo assembled transcriptomes and automatic orthology prediction methods. The analysis of a concatenated data set of 2,779 genes (411,138 amino acids) with about 78% gene occupancy and a reduced version with 95% gene occupancy, under evolutionary models accounting or not for site-specific amino acid replacement patterns results in a well-supported phylogeny that recovers all major accepted Nemertean clades with the monophyly of HeteroNemertea, HoploNemertea, Monostilifera, being well supported. Significantly, all the ambiguous patterns inferred from Sanger-based approaches were resolved, namely the monophyly of PalaeoNemertea and Pilidiophora. By testing for possible conflict in the analyzed supermatrix, we observed that concatenation was the best solution, and the results of the analyses should settle prior debates on Nemertean phylogeny. The study highlights the importance, feasibility, and completeness of Illumina-based phylogenomic data matrices.
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disentangling ribbon worm relationships multi locus analysis supports traditional classification of the phylum Nemertea
Cladistics, 2012Co-Authors: Sónia C. S. Andrade, Hiroshi Kajihara, Jörn Von Döhren, Malin Strand, Megan L. Schwartz, Juan Junoy, Haixia Chen, Shichun Sun, Martin Thiel, Jon L. NorenburgAbstract:The phylogenetic relationships of selected members of the phylum Nemertea are explored by means of six markers amplified from the genomic DNA of freshly collected specimens (the nuclear 18S rRNA and 28S rRNA genes, histones H3 and H4, and the mitochondrial genes 16S rRNA and cytochrome c oxidase subunit I). These include all previous markers and regions used in earlier phylogenetic analyses of Nemerteans, therefore acting as a scaffold to which one could pinpoint any previously published study. Our results, based on analyses of static and dynamic homology concepts under probabilistic and parsimony frameworks, agree in the non-monophyly of PalaeoNemertea and in the monophyly of Heteronemerta and HoploNemertea. The position of Hubrechtella and the Pilidiophora hypothesis are, however, sensitive to analytical method, as is the monophyly of the non-hubrechtiid palaeoNemerteans. Our results are, however, consistent with the main division of HoploNemertea into Polystilifera and Monostilifera, the last named being divided into CrateNemertea and DistromatoNemertea, as well as into the main division of HeteroNemertea into Baseodiscus and the remaining species. The study also continues to highlight the deficient taxonomy at the family and generic level within Nemertea and sheds light on the areas of the tree that require further refinement. � The Willi Hennig Society 2011.
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Disentangling ribbon worm relationships: multi‐locus analysis supports traditional classification of the phylum Nemertea
Cladistics, 2011Co-Authors: Sónia C. S. Andrade, Hiroshi Kajihara, Jörn Von Döhren, Malin Strand, Megan L. Schwartz, Juan Junoy, Haixia Chen, Shichun Sun, Martin Thiel, Jon L. NorenburgAbstract:The phylogenetic relationships of selected members of the phylum Nemertea are explored by means of six markers amplified from the genomic DNA of freshly collected specimens (the nuclear 18S rRNA and 28S rRNA genes, histones H3 and H4, and the mitochondrial genes 16S rRNA and cytochrome c oxidase subunit I). These include all previous markers and regions used in earlier phylogenetic analyses of Nemerteans, therefore acting as a scaffold to which one could pinpoint any previously published study. Our results, based on analyses of static and dynamic homology concepts under probabilistic and parsimony frameworks, agree in the non-monophyly of PalaeoNemertea and in the monophyly of Heteronemerta and HoploNemertea. The position of Hubrechtella and the Pilidiophora hypothesis are, however, sensitive to analytical method, as is the monophyly of the non-hubrechtiid palaeoNemerteans. Our results are, however, consistent with the main division of HoploNemertea into Polystilifera and Monostilifera, the last named being divided into CrateNemertea and DistromatoNemertea, as well as into the main division of HeteroNemertea into Baseodiscus and the remaining species. The study also continues to highlight the deficient taxonomy at the family and generic level within Nemertea and sheds light on the areas of the tree that require further refinement. � The Willi Hennig Society 2011.
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dinonemertes shinkaii sp nov Nemertea hoploNemertea polystilifera pelagica a new species of bathypelagic Nemertean
Zootaxa, 2010Co-Authors: Hiroshi Kajihara, Dhugal J LindsayAbstract:A new species of bathypelagic polystiliferous Nemertean Dinonemertes shinkaii is described based on the holotype obtained by the manned submersible Shinkai 6500 from a depth of 2343 m in Japan Trench, Northwest Pacific. Dinonemertes shinkaii can be distinguished from its congeners in having a translucent body, 24 proboscis nerves, two pairs of intestinal caecal diverticula, and about 25 pairs of intestinal lateral diverticula. This species represents the first dinonemertid to have pseudostriated muscle fibres in the rhynchocoel circular muscle layers.
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Character-matrix based descriptions of two new Nemertean (Nemertea) species
Zoological Journal of the Linnean Society, 2009Co-Authors: Per Sundberg, Hiroshi Kajihara, Alexey V. Chernyshev, Tobias Kånneby, Malin StrandAbstract:Ribbon worms (phylum Nemertea) have traditionally been described and classified based on a combination of internal and external morphological characters. The extent, and wealth of details, of these ...
Shichun Sun - One of the best experts on this subject based on the ideXlab platform.
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complete mitochondrial genome sequences of two parasitic commensal Nemerteans gononemertes parasita and nemertopsis tetraclitophila Nemertea hoploNemertea
Parasites & Vectors, 2014Co-Authors: Wen-yan Sun, Per Sundberg, Malin Strand, Haixia Chen, Wei Shi, Shichun SunAbstract:Background Most Nemerteans (phylum Nemertea) are free-living, but about 50 species are known to be firmly associated with other marine invertebrates. For example, Gononemertes parasita is associated with ascidians, and Nemertopsis tetraclitophila with barnacles. There are 12 complete or near-complete mitochondrial genome (mitogenome) sequences of Nemerteans available in GenBank, but no mitogenomes of none free-living Nemerteans have been determined so far. In the present paper complete mitogenomes of the above two parasitic/commensal Nemerteans are reported.
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mutation and selection cause codon usage and bias in mitochondrial genomes of ribbon worms Nemertea
PLOS ONE, 2014Co-Authors: Haixia Chen, Jon L. Norenburg, Shichun Sun, Per SundbergAbstract:The phenomenon of codon usage bias is known to exist in many genomes and it is mainly determined by mutation and selection. To understand the patterns of codon usage in Nemertean mitochondrial genomes, we use bioinformatic approaches to analyze the protein-coding sequences of eight Nemertean species. Neutrality analysis did not find a significant correlation between GC12 and GC3. ENc-plot showed a few genes on or close to the expected curve, but the majority of points with low-ENc values are below it. ENc-plot suggested that mutational bias plays a major role in shaping codon usage. The Parity Rule 2 plot (PR2) analysis showed that GC and AT were not used proportionally and we propose that codons containing A or U at third position are used preferentially in Nemertean species, regardless of whether corresponding tRNAs are encoded in the mitochondrial DNA. Context-dependent analysis indicated that the nucleotide at the second codon position slightly affects synonymous codon choices. These results suggested that mutational and selection forces are probably acting to codon usage bias in Nemertean mitochondrial genomes.
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The complete mitochondrial genome of Iwatanemertes piperata (Nemertea: HeteroNemertea)
Mitochondrial DNA, 2014Co-Authors: Chun-yang Shen, Wen-yan Sun, Shichun SunAbstract:The complete mitochondrial genome of Iwatanemertes piperata (Nemertea: HeteroNemertea) was determined. The genome, which contains 13 protein-coding genes, 2 ribosomal RNA genes and 22 transfer RNA genes, is 16,382 bp in length and has a base composition of G (25.87%), A (21.53%), T (40.64%) and C (11.95%). The gene order is identical to other HeteroNemertea mitogenomes published to date.
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Complete mitochondrial genome sequences of two parasitic/commensal Nemerteans, Gononemertes parasita and Nemertopsis tetraclitophila (Nemertea: HoploNemertea)
Parasites & Vectors, 2014Co-Authors: Wen-yan Sun, Per Sundberg, Malin Strand, Haixia Chen, Wei Shi, Shichun SunAbstract:Background Most Nemerteans (phylum Nemertea) are free-living, but about 50 species are known to be firmly associated with other marine invertebrates. For example, Gononemertes parasita is associated with ascidians, and Nemertopsis tetraclitophila with barnacles. There are 12 complete or near-complete mitochondrial genome (mitogenome) sequences of Nemerteans available in GenBank, but no mitogenomes of none free-living Nemerteans have been determined so far. In the present paper complete mitogenomes of the above two parasitic/commensal Nemerteans are reported.
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a comparative study of Nemertean complete mitochondrial genomes including two new ones for nectonemertes cf mirabilis and zygeupolia rubens may elucidate the fundamental pattern for the phylum Nemertea
BMC Genomics, 2012Co-Authors: Per Sundberg, Haixia Chen, Shichun Sun, Weicheng Ren, Jon L. NorenburgAbstract:The mitochondrial genome is important for studying genome evolution as well as reconstructing the phylogeny of organisms. Complete mitochondrial genome sequences have been reported for more than 2200 metazoans, mainly vertebrates and arthropods. To date, from a total of about 1275 described Nemertean species, only three complete and two partial mitochondrial DNA sequences from Nemerteans have been published. Here, we report the entire mitochondrial genomes for two more Nemertean species: Nectonemertes cf. mirabilis and Zygeupolia rubens. The sizes of the entire mitochondrial genomes are 15365 bp for N. cf. mirabilis and 15513 bp for Z. rubens. Each circular genome contains 37 genes and an AT-rich non-coding region, and overall nucleotide composition is AT-rich. In both species, there is significant strand asymmetry in the distribution of nucleotides, with the coding strand being richer in T than A and in G than C. The AT-rich non-coding regions of the two genomes have some repeat sequences and stem-loop structures, both of which may be associated with the initiation of replication or transcription. The 22 tRNAs show variable substitution patterns in Nemerteans, with higher sequence conservation in genes located on the H strand. Gene arrangement of N. cf. mirabilis is identical to that of Paranemertes cf. peregrina, both of which are HoploNemertea, while that of Z. rubens is the same as in Lineus viridis, both of which are HeteroNemertea. Comparison of the gene arrangements and phylogenomic analysis based on concatenated nucleotide sequences of the 12 mitochondrial protein-coding genes revealed that species with closer relationships share more identical gene blocks. The two new mitochondrial genomes share many features, including gene contents, with other known Nemertean mitochondrial genomes. The tRNA families display a composite substitution pathway. Gene order comparison to the proposed ground pattern of Bilateria and some lophotrochozoans suggests that the Nemertean ancestral mitochondrial gene order most closely resembles the heteroNemertean type. Phylogenetic analysis proposes a sister-group relationship between Hetero- and HoploNemertea, which supports one of two recent alternative hypotheses of Nemertean phylogeny.
Martin Thiel - One of the best experts on this subject based on the ideXlab platform.
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Activity patterns and predatory behavior of an intertidal Nemertean from rocky shores: Prosorhochmus nelsoni (HoploNemertea) from the Southeast Pacific
Marine Biology, 2012Co-Authors: Serena A. Caplins, J.m. Turbeville, Miguel Angel Penna-diaz, Erick Godoy, Nelson Valdivia, Martin ThielAbstract:Understanding the impact of environmental stressors on predator activity is a prerequisite to understanding the underlying mechanisms shaping community structure. The Nemertean Prosorhochmus nelsoni is a common predator in the mid-intertidal zone on rocky shores along the Chilean coast, where it can reach very high abundances (up to 260 ind m^−2) in algal turfs, algal crusts, barnacle crusts, and mixed substrata. Tidal and diurnal scans revealed that the activity of P. nelsoni is primarily restricted to night and early-morning low tides and is relatively low when air temperatures are high. On average, larger worms crawled faster than smaller worms, with their maximum velocity being influenced by substratum type. Their estimated rate of predation is 0.092 prey items Nemertean^−1 day^−1, just below the laboratory rate of ~0.2 amphipods Nemertean^−1 day^−1 previously estimated for this species. P. nelsoni consumes a diverse spectrum of prey items (i.e., amphipods, isopods, decapods, barnacles, and dipterans) and is possibly exerting a significant influence on its prey populations. We suggest that the opportunistic predatory behavior of this intertidal predator is caused by the trade-off between immediate persistence (e.g., avoidance of desiccation) and long-term survival through successful foraging.
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disentangling ribbon worm relationships multi locus analysis supports traditional classification of the phylum Nemertea
Cladistics, 2012Co-Authors: Sónia C. S. Andrade, Hiroshi Kajihara, Jörn Von Döhren, Malin Strand, Megan L. Schwartz, Juan Junoy, Haixia Chen, Shichun Sun, Martin Thiel, Jon L. NorenburgAbstract:The phylogenetic relationships of selected members of the phylum Nemertea are explored by means of six markers amplified from the genomic DNA of freshly collected specimens (the nuclear 18S rRNA and 28S rRNA genes, histones H3 and H4, and the mitochondrial genes 16S rRNA and cytochrome c oxidase subunit I). These include all previous markers and regions used in earlier phylogenetic analyses of Nemerteans, therefore acting as a scaffold to which one could pinpoint any previously published study. Our results, based on analyses of static and dynamic homology concepts under probabilistic and parsimony frameworks, agree in the non-monophyly of PalaeoNemertea and in the monophyly of Heteronemerta and HoploNemertea. The position of Hubrechtella and the Pilidiophora hypothesis are, however, sensitive to analytical method, as is the monophyly of the non-hubrechtiid palaeoNemerteans. Our results are, however, consistent with the main division of HoploNemertea into Polystilifera and Monostilifera, the last named being divided into CrateNemertea and DistromatoNemertea, as well as into the main division of HeteroNemertea into Baseodiscus and the remaining species. The study also continues to highlight the deficient taxonomy at the family and generic level within Nemertea and sheds light on the areas of the tree that require further refinement. � The Willi Hennig Society 2011.
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Disentangling ribbon worm relationships: multi‐locus analysis supports traditional classification of the phylum Nemertea
Cladistics, 2011Co-Authors: Sónia C. S. Andrade, Hiroshi Kajihara, Jörn Von Döhren, Malin Strand, Megan L. Schwartz, Juan Junoy, Haixia Chen, Shichun Sun, Martin Thiel, Jon L. NorenburgAbstract:The phylogenetic relationships of selected members of the phylum Nemertea are explored by means of six markers amplified from the genomic DNA of freshly collected specimens (the nuclear 18S rRNA and 28S rRNA genes, histones H3 and H4, and the mitochondrial genes 16S rRNA and cytochrome c oxidase subunit I). These include all previous markers and regions used in earlier phylogenetic analyses of Nemerteans, therefore acting as a scaffold to which one could pinpoint any previously published study. Our results, based on analyses of static and dynamic homology concepts under probabilistic and parsimony frameworks, agree in the non-monophyly of PalaeoNemertea and in the monophyly of Heteronemerta and HoploNemertea. The position of Hubrechtella and the Pilidiophora hypothesis are, however, sensitive to analytical method, as is the monophyly of the non-hubrechtiid palaeoNemerteans. Our results are, however, consistent with the main division of HoploNemertea into Polystilifera and Monostilifera, the last named being divided into CrateNemertea and DistromatoNemertea, as well as into the main division of HeteroNemertea into Baseodiscus and the remaining species. The study also continues to highlight the deficient taxonomy at the family and generic level within Nemertea and sheds light on the areas of the tree that require further refinement. � The Willi Hennig Society 2011.
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Status of the Nemertea as predators in marine ecosystems
Hydrobiologia, 2001Co-Authors: Martin Thiel, Inken KruseAbstract:The ecology of Nemertean predators in marine ecosystems is reviewed. Nemerteans occur in most marine environments although usually in low abundances. Some species, particularly in intertidal habitats, may reach locally high densities. During specific time periods appropriate for hunting, Nemerteans roam about in search of prey. Upon receiving a stimulus (usually chemical cues), many Nemertean species actively pursue their prey and follow them into their dwellings or in their tracks. Other species (many hoploNemerteans) adopt a sit-and-wait strategy, awaiting prey items in strategic locations. Nemerteans possess potent neurotoxins, killing even highly mobile prey species within a few seconds and within the activity range of its attacker. Most Nemertean species prey on live marine invertebrates, but some also gather on recently dead organisms to feed on them. HeteroNemerteans preferentially feed on polychaetes, while most hoploNemerteans prey on small crustaceans. The species examined to date show strong preferences for selected prey species, but will attack a variety of alternative prey organisms when deprived of their favourite species. Ontogenetic changes in prey selection appear to occur, but no further information about, e.g. size selection, is available. Feeding rates as revealed from short-term laboratory experiments range on the order of 1–5 prey items d^−1. These values apparently are overestimates, since long-term experiments report substantially lower values (0.05–0.3 prey items d^−1). Nemerteans have been reported to exert a strong impact on the population size of their prey organisms through their predation activity. Considering low predation rates, these effects may primarily be a result of indirect and additive interactions. We propose future investigations on these interactive effects in combination with other predators. Another main avenue of Nemertean ecological research appears to be the examination of their role in highly structured habitats such as intertidal rocky shore and coral reef environments.
