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Kenneth M. Halanych - One of the best experts on this subject based on the ideXlab platform.
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Multiple introns in a deep-sea Annelid (Decemunciger: Ampharetidae) mitochondrial genome.
Scientific reports, 2017Co-Authors: Angelo F. Bernardino, Craig R. Smith, Kenneth M. HalanychAbstract:Wood falls provide episodic fluxes of energy to the sea floor that are degraded by a species-rich benthic fauna. Part of this rich diversity includes Annelid polychaetes but unfortunately, our understanding of such fauna is limited and their genetic variability and evolutionary origins remain poorly known. In this study, we sequenced complete mitochondrial genomes from three congeneric Decemunciger (Ampharetidae) individuals that had colonized multiple wood falls in the deep (~1600 m) NE Pacific Ocean. Mitochondrial gene order within Decemunciger was similar to the three other available Terebellomorpha genomes, consistent with the relatively conserved nature of mitochondrial genomes within Annelids. Unexpectedly, we found introns within the cox1, nad1 and nad4 genes of all three genomes assembled. This is the greatest number of introns observed in Annelid mtDNA genomes, and possibly in bilaterians. Interestingly, the introns were of variable sizes suggesting possible evolutionary differences in the age and origins of introns. The sequence of the introns within cox1 is similar to Group II introns previously identified, suggesting that introns in the mitochondrial genome of Annelids may be more widespread then realized. Phylogenetically, Decemunciger appears to be a sister clade among current vent and seep deep-sea Ampharetinae.
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Discovery and evolution of novel hemerythrin genes in Annelid worms.
BMC evolutionary biology, 2017Co-Authors: Elisa M. Costa-paiva, Scott R Santos, Nathan V. Whelan, Damien S. Waits, Carlos G. Schrago, Kenneth M. HalanychAbstract:Despite extensive study on hemoglobins and hemocyanins, little is known about hemerythrin (Hr) evolutionary history. Four subgroups of Hrs have been documented, including: circulating Hr (cHr), myohemerythrin (myoHr), ovohemerythrin (ovoHr), and neurohemerythrin (nHr). Annelids have the greatest diversity of oxygen carrying proteins among animals and are the only phylum in which all Hr subgroups have been documented. To examine Hr diversity in Annelids and to further understand evolution of Hrs, we employed approaches to survey Annelid transcriptomes in silico. Sequences of 214 putative Hr genes were identified from 44 Annelid species in 40 different families and Bayesian inference revealed two major clades with strong statistical support. Notably, the topology of the Hr gene tree did not mirror the phylogeny of Annelida as presently understood, and we found evidence of extensive Hr gene duplication and loss in Annelids. Gene tree topology supported monophyly of cHrs and a myoHr clade that included nHrs sequences, indicating these designations are functional rather than evolutionary. The presence of several cHrs in early branching taxa suggests that a variety of Hrs were present in the common ancestor of extant Annelids. Although our analysis was limited to expressed-coding regions, our findings demonstrate a greater diversity of Hrs among Annelids than previously reported.
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The Evolution of Annelids Reveals Two Adaptive Routes to the Interstitial Realm
Current biology : CB, 2015Co-Authors: Torsten H. Struck, Anja Golombek, Wilfried Westheide, Gunter Purschke, Anne Weigert, Christoph Bleidorn, Franziska Anni Franke, Kenneth M. HalanychAbstract:Summary Many animals permanently inhabit the marine interstitium, the space between sand grains [1, 2]. Different evolutionary scenarios may explain the existence of interstitial animals [3, 4]. These scenarios include (1) that the interstitial realm is the ancestral habitat of bilaterians [5, 6], (2) that interstitial taxa evolved from larger ancestors by miniaturization, or (3) progenesis [3]. The first view mirrors the former hypothesis that interstitial Annelids, called archiAnnelids, were at the base of the Annelid radiation [7]. Based on morphological data, however, progenesis is generally favored for interstitial Annelids today [3, 4, 8]. Herein, our phylogenomic approach revealed that interstitial archiAnnelids are robustly placed into two groups nested within the Annelid tree. Evolution of the first group comprising among others Dinophilidae is best explained by progenesis. In contrast, the second group comprising Protodrilida and Polygordiidae appears to have evolved by stepwise miniaturization adapting from coarser to finer sediments. Thus, in addition to progenesis [3, 4], miniaturization, thought to be too slow for an adaptation to the interstitium [3], is an important second route allowing adaptation to interstitial environments. Both progenesis and miniaturization should be considered when investigating evolution of interstitial taxa [1, 3].
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illuminating the base of the Annelid tree using transcriptomics
Molecular Biology and Evolution, 2014Co-Authors: Matthias Meyer, Detlev Arendt, Kenneth M. Halanych, Birgit Nickel, Bernhard Hausdorf, Scott R Santos, Gunter PurschkeAbstract:Annelida is one of three animal groups possessing segmentation and is central in considerations about the evolution of different character traits. It has even been proposed that the bilaterian ancestor resembled an Annelid. However, a robust phylogeny of Annelida, especially with respect to the basal relationships, has been lacking. Our study based on transcriptomic data comprising 68,750-170,497 amino acid sites from 305 to 622 proteins resolves Annelid relationships, including Chaetopteridae, Amphinomidae, Sipuncula, Oweniidae, and Magelonidae in the basal part of the tree. Myzostomida, which have been indicated to belong to the basal radiation as well, are now found deeply nested within Annelida as sister group to Errantia in most analyses. On the basis of our reconstruction of a robust Annelid phylogeny, we show that the basal branching taxa include a huge variety of life styles such as tube dwelling and deposit feeding, endobenthic and burrowing, tubicolous and filter feeding, and errant and carnivorous forms. Ancestral character state reconstruction suggests that the ancestral Annelid possessed a pair of either sensory or grooved palps, bicellular eyes, biramous parapodia bearing simple chaeta, and lacked nuchal organs. Because the oldest fossil of Annelida is reported for Sipuncula (520 Ma), we infer that the early diversification of Annelids took place at least in the Lower Cambrian.
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Unsegmented Annelids? Possible Origins of Four Lophotrochozoan Worm Taxa 1
2013Co-Authors: Kenneth M. Halanych, Thomas G. Dahlgren, Damhnait MchughAbstract:SYNOPSIS. In traditional classification schemes, the Annelida consists of the Polychaeta and the Clitellata (the latter including the Oligochaeta and Hirudinida). However, recent analyses suggest that Annelids are much more diverse than traditionally believed, and that polychaetes are paraphyletic. Specifically, some lesser-known taxa (previously regarded as separate phyla) appear to fall within the Annelid radiation. Abundant molecular, developmental, and morphological data show that the Siboglinidae, which includes the formerly recognized Pogonophora and Vestimentifera, are derived Annelids; recent data from the Elongation Factor-1 � (EF-1�) gene also suggest that echiurids are of Annelid ancestry. Further, the phylogenetic origins of two other lesser-known groups of marine worms, the Myzostomida and Sipuncula, have recently been called into question. Whereas some authors advocate Annelid affinities, others argue that these taxa do not fall within the Annelid radiation. With advances in our understanding of Annelid phylogeny, our perceptions of body plan evolution within the Metazoa are changing. The evolution of segmentation probably is more plastic than traditionally believed. However, as our understanding of organismal evolution is being revised, we are also forced to reconsider the specific characters being examined. Should segmentation be considered a developmental process or an ontological endpoint? The Annelida is a pivotal taxon for understandin
Torsten H. Struck - One of the best experts on this subject based on the ideXlab platform.
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Convergent evolution of the ladder-like ventral nerve cord in Annelida
Frontiers in zoology, 2018Co-Authors: Conrad Helm, Torsten H. Struck, Thomas Bartolomaeus, Patrick Beckers, Stephan Drukewitz, Ioannis Kourtesis, Anne Weigert, GĂźnter Purschke, Katrine Worsaae, Christoph Bleidorn, Anne Weigert, Christoph BleidornAbstract:A median, segmented, Annelid nerve cord has repeatedly been compared to the arthropod and vertebrate nerve cords and became the most used textbook representation of the Annelid nervous system. Recent phylogenomic analyses, however, challenge the hypothesis that a subepidermal rope-ladder-like ventral nerve cord (VNC) composed of a paired serial chain of ganglia and somata-free connectives represents either a plesiomorphic or a typical condition in Annelids. Using a comparative approach by combining phylogenomic analyses with morphological methods (immunohistochemistry and CLSM, histology and TEM), we compiled a comprehensive dataset to reconstruct the evolution of the Annelid VNC. Our phylogenomic analyses generally support previous topologies. However, the so far hard-to-place Apistobranchidae and Psammodrilidae are now incorporated among the basally branching Annelids with high support. Based on this topology we reconstruct an intraepidermal VNC as the ancestral state in Annelida. Thus, a subepidermal ladder-like nerve cord clearly represents a derived condition. Based on the presented data, a ladder-like appearance of the ventral nerve cord evolved repeatedly, and independently of the transition from an intraepidermal to a subepidermal cord during Annelid evolution. Our investigations thereby propose an alternative set of neuroanatomical characteristics for the last common ancestor of Annelida or perhaps even Spiralia.
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Breaking the ladder: Evolution of the ventral nerve cord in Annelida
2018Co-Authors: Conrad Helm, Torsten H. Struck, Thomas Bartolomaeus, Patrick Beckers, Stephan Drukewitz, Ioannis Kourtesis, Anne Weigert, GĂźnter Purschke, Katrine Worsaae, Christoph Bleidorn, Anne Weigert, Christoph BleidornAbstract:A median, segmented, Annelid nerve cord has repeatedly been compared to the arthropod and vertebrate nerve cords and became the most used textbook representation of the Annelid nervous system. Recent phylogenomic analyses, however, challenge the hypothesis that a subepidermal rope-ladder-like ventral nerve cord (VNC) composed of a paired serial chain of ganglia and somata-free connectives represents neither a plesiomorphic nor a typical condition in Annelids. Using a comparative approach by combining phylogenomic analyses with morphological methods (immunohistochemistry and CLSM, histology and TEM), we compiled a comprehensive dataset to reconstruct the evolution of the Annelid VNC. Our phylogenomic analyses generally support previous topologies. However, the so far hard-to-place Apistobranchidae and Psammodrilidae are now incorporated among the basally branching Annelids with high support. Based on this topology we reconstruct an intraepidermal VNC as ancestral state in Annelida. Thus, a subepidermal ladder-like nerve cord clearly represents a derived condition. Based on the presented data, a ladder-like appearance of the ventral nerve cord evolved repeatedly, and independently of the transition from an intraepidermal to a subepidermal cord during Annelid evolution. Our investigations thereby question a common origin of the bilaterian median ganglionated VNC and propose an alternative set of neuroanatomical characteristics of the last common ancestor of Annelida or perhaps even Spiralia.
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Evolution of mitochondrial gene order in Annelida.
Molecular phylogenetics and evolution, 2015Co-Authors: Anja Golombek, Michael Gerth, Francine Schwarz, Torsten H. StruckAbstract:Annelida is a highly diverse animal group with over 21,000 described species. As part of Lophotrochozoa, the vast majority of Annelids are currently classified into two groups: Errantia and Sedentaria, together forming PleistoAnnelida. Besides these taxa, Sipuncula, Amphinomidae, Chaetopteridae, Oweniidae and Magelonidae can be found branching at the base of the tree. Comparisons of mitochondrial genomes have been used to investigate phylogenetic relationship within animal taxa. Complete Annelid mitochondrial genomes are available for some Sedentaria and Errantia and in most cases exhibit a highly conserved gene order. Only two complete genomes have been published from the basal branching lineages and these are restricted to Sipuncula. We describe the first complete mitochondrial genome sequences for all other basal branching Annelid families: Owenia fusiformis (Oweniidae), Magelona mirabilis (Magelonidae), Eurythoe complanata (Amphinomidae), Chaetopterus variopedatus and Phyllochaetopterus sp. (Chaetopteridae). The mitochondrial gene order of all these taxa is substantially different from the pattern found in PleistoAnnelida. Additionally, we report the first mitochondrial genomes in Annelida that encode genes on both strands. Our findings demonstrate that the supposedly highly conserved mitochondrial gene order suggested for Annelida is restricted to PleistoAnnelida, representing the ground pattern of this group. All investigated basal branching Annelid taxa show a completely different arrangement of genes than observed in PleistoAnnelida. The gene order of protein coding and ribosomal genes in Magelona mirabilis differs only in two transposition events from a putative lophotrochozoan ground pattern and might be the closest to an ancestral Annelid pattern. The mitochondrial genomes of Myzostomida show the conserved pattern of PleistoAnnelida, thereby supporting their inclusion in this taxon.
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The Evolution of Annelids Reveals Two Adaptive Routes to the Interstitial Realm
Current biology : CB, 2015Co-Authors: Torsten H. Struck, Anja Golombek, Wilfried Westheide, Gunter Purschke, Anne Weigert, Christoph Bleidorn, Franziska Anni Franke, Kenneth M. HalanychAbstract:Summary Many animals permanently inhabit the marine interstitium, the space between sand grains [1, 2]. Different evolutionary scenarios may explain the existence of interstitial animals [3, 4]. These scenarios include (1) that the interstitial realm is the ancestral habitat of bilaterians [5, 6], (2) that interstitial taxa evolved from larger ancestors by miniaturization, or (3) progenesis [3]. The first view mirrors the former hypothesis that interstitial Annelids, called archiAnnelids, were at the base of the Annelid radiation [7]. Based on morphological data, however, progenesis is generally favored for interstitial Annelids today [3, 4, 8]. Herein, our phylogenomic approach revealed that interstitial archiAnnelids are robustly placed into two groups nested within the Annelid tree. Evolution of the first group comprising among others Dinophilidae is best explained by progenesis. In contrast, the second group comprising Protodrilida and Polygordiidae appears to have evolved by stepwise miniaturization adapting from coarser to finer sediments. Thus, in addition to progenesis [3, 4], miniaturization, thought to be too slow for an adaptation to the interstitium [3], is an important second route allowing adaptation to interstitial environments. Both progenesis and miniaturization should be considered when investigating evolution of interstitial taxa [1, 3].
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Mitochondrial genomes to the rescue - Diurodrilidae in the myzostomid trap
Molecular Phylogenetics and Evolution, 2013Co-Authors: Anja Golombek, Sarah Tobergte, Maximilian P. Nesnidal, Torsten H. StruckAbstract:Abstract Diurodrilidae is a taxon of Lophotrochozoa comprising about six, exclusively interstitial species, which are up to 500 μm long and dorsoventrally flattened. Traditionally, Diurodrilidae had been regarded as an Annelid family. However, recently Diurodrilidae had been excluded from Annelida and been placed in closer relationship to platyzoan taxa based on both morphological and nuclear rRNA data. Since both, Diurodrilidae and platyzoan taxa, exhibit long branches in the molecular analyses, the close relationship might be due to a long branch attraction artifact. The Annelid taxon Myzostomida had been trapped in a similar long branch attraction artifact with platyzoan taxa using nuclear rRNA data, but determination of the nearly complete mitochondrial genome of myzostomids revealed their Annelid affinity. Therefore, we determined the nearly complete mitochondrial genome of Diurodrilus subterraneus as well as new nuclear rRNA data for D. subterraneus and some platyzoan taxa. All our analyses of nuclear rRNA and mitochondrial sequence and gene order data presented herein clearly place Diurodrilidae within Annelida and with strong nodal support values in some analyses. Therefore, the previously suggested exclusion of Diurodrilidae from Annelida and its close relationship with platyzoan taxa can be attributed to a long branch artifact. Morphological data do not unambiguously support a platyzoan affinity of Diurodrilidae, but instead would also be in line with a progenetic origin of Diurodrilidae within Annelida.
Damhnait Mchugh - One of the best experts on this subject based on the ideXlab platform.
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Unsegmented Annelids? Possible Origins of Four Lophotrochozoan Worm Taxa 1
2013Co-Authors: Kenneth M. Halanych, Thomas G. Dahlgren, Damhnait MchughAbstract:SYNOPSIS. In traditional classification schemes, the Annelida consists of the Polychaeta and the Clitellata (the latter including the Oligochaeta and Hirudinida). However, recent analyses suggest that Annelids are much more diverse than traditionally believed, and that polychaetes are paraphyletic. Specifically, some lesser-known taxa (previously regarded as separate phyla) appear to fall within the Annelid radiation. Abundant molecular, developmental, and morphological data show that the Siboglinidae, which includes the formerly recognized Pogonophora and Vestimentifera, are derived Annelids; recent data from the Elongation Factor-1 � (EF-1�) gene also suggest that echiurids are of Annelid ancestry. Further, the phylogenetic origins of two other lesser-known groups of marine worms, the Myzostomida and Sipuncula, have recently been called into question. Whereas some authors advocate Annelid affinities, others argue that these taxa do not fall within the Annelid radiation. With advances in our understanding of Annelid phylogeny, our perceptions of body plan evolution within the Metazoa are changing. The evolution of segmentation probably is more plastic than traditionally believed. However, as our understanding of organismal evolution is being revised, we are also forced to reconsider the specific characters being examined. Should segmentation be considered a developmental process or an ontological endpoint? The Annelida is a pivotal taxon for understandin
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Annelid phylogeny and the status of Sipuncula and Echiura
BMC evolutionary biology, 2007Co-Authors: Torsten H. Struck, Damhnait Mchugh, Nancy Schult, Tiffany Kusen, Emily Hickman, Kenneth M. HalanychAbstract:Annelida comprises an ancient and ecologically important animal phylum with over 16,500 described species and members are the dominant macrofauna of the deep sea. Traditionally, two major groups are distinguished: Clitellata (including earthworms, leeches) and "Polychaeta" (mostly marine worms). Recent analyses of molecular data suggest that Annelida may include other taxa once considered separate phyla (i.e., Echiura, and Sipuncula) and that Clitellata are derived Annelids, thus rendering "Polychaeta" paraphyletic; however, this contradicts classification schemes of Annelids developed from recent analyses of morphological characters. Given that deep-level evolutionary relationships of Annelida are poorly understood, we have analyzed comprehensive datasets based on nuclear and mitochondrial genes, and have applied rigorous testing of alternative hypotheses so that we can move towards the robust reconstruction of Annelid history needed to interpret animal body plan evolution. Sipuncula, Echiura, Siboglinidae, and Clitellata are all nested within polychaete Annelids according to phylogenetic analyses of three nuclear genes (18S rRNA, 28S rRNA, EF1α; 4552 nucleotide positions analyzed) for 81 taxa, and 11 nuclear and mitochondrial genes for 10 taxa (additional: 12S rRNA, 16S rRNA, ATP8, COX1-3, CYTB, NAD6; 11,454 nucleotide positions analyzed). For the first time, these findings are substantiated using approximately unbiased tests and non-scaled bootstrap probability tests that compare alternative hypotheses. For echiurans, the polychaete group Capitellidae is corroborated as the sister taxon; while the exact placement of Sipuncula within Annelida is still uncertain, our analyses suggest an affiliation with terebellimorphs. Siboglinids are in a clade with other sabellimorphs, and clitellates fall within a polychaete clade with aeolosomatids as their possible sister group. None of our analyses support the major polychaete clades reflected in the current classification scheme of Annelids, and hypothesis testing significantly rejects monophyly of Scolecida, Palpata, Canalipalpata, and Aciculata. Using multiple genes and explicit hypothesis testing, we show that Echiura, Siboglinidae, and Clitellata are derived Annelids with polychaete sister taxa, and that Sipuncula should be included within Annelids. The traditional composition of Annelida greatly underestimates the morphological diversity of this group, and inclusion of Sipuncula and Echiura implies that patterns of segmentation within Annelids have been evolutionarily labile. Relationships within Annelida based on our analyses of multiple genes challenge the current classification scheme, and some alternative hypotheses are provided.
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Molecular systematics of polychaetes (Annelida)
Hydrobiologia, 2005Co-Authors: Damhnait MchughAbstract:Some progress has been made in the field of molecular systematics of polychaetes over the past couple of years. In particular, phylogenetic analyses of sequence data from the 18S rRNA gene have included increasing numbers of taxa, and explicit hypothesis testing of sister-group relationships is being incorporated into the most recent studies. An increasing number of analyses of relationships within polychaete groups are being undertaken, with specific inferences being drawn regarding the evolution of characters such as reproductive mode. Despite this progress, the unanswered questions regarding Annelid relationships outlined by McHugh (2000, p. 1881) remain: “what are the relationships among the polychaete Annelids, what group is sister to the Clitellata, what extant group is most basal on the Annelid tree, and what group is sister to Annelida?” Continued expansion of taxon sampling and further combined investigation of conserved nuclear coding genes, in conjunction with rRNA genes, may help to resolve some of these issues. Furthermore, only by expanding molecular systematic studies of polychaetes to analyses of nuclear coding genes for comprehensive taxon samples will it become clear whether the lack of basal-node resolution observed in analyses of 18S rRNA reflects a rapid radiation of the group, or is a feature associated with the 18S rRNA gene itself. Genomic-level data (e.g., mitochondrial gene order) may also be informative, and the cautious use of gene copies in phylogenetic analyses may point to a root of the Annelid tree.
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Unsegmented Annelids? Possible Origins of Four Lophotrochozoan Worm Taxa
Integrative and comparative biology, 2002Co-Authors: Kenneth M. Halanych, Thomas G. Dahlgren, Damhnait MchughAbstract:SYNOPSIS. In traditional classification schemes, the Annelida consists of the Polychaeta and the Clitellata (the latter including the Oligochaeta and Hirudinida). However, recent analyses suggest that Annelids are much more diverse than traditionally believed, and that polychaetes are paraphyletic. Specifically, some lesser-known taxa (previously regarded as separate phyla) appear to fall within the Annelid radiation. Abundant molecular, developmental, and morphological data show that the Siboglinidae, which includes the formerly recognized Pogonophora and Vestimentifera, are derived Annelids; recent data from the Elongation Factor-1 a (EF-1a) gene also suggest that echiurids are of Annelid ancestry. Further, the phylogenetic origins of two other lesser-known groups of marine worms, the Myzostomida and Sipuncula, have recently been called into question. Whereas some authors advocate Annelid affinities, others argue that these taxa do not fall within the Annelid radiation. With advances in our understanding of Annelid phylogeny, our perceptions of body plan evolution within the Metazoa are changing. The evolution of segmentation probably is more plastic than traditionally believed. However, as our understanding of organismal evolution is being revised, we are also forced to reconsider the specific characters being examined. Should segmentation be considered a developmental process or an ontological endpoint? The Annelida is a pivotal taxon for understanding metazoan evolution, as our interpretation of bilaterian phylogeny, development, and macroevolutionary trends are influenced by current concepts of Annelid ancestry and evolution. For example, the Articulata hypothesis posits that arthropods and Annelids are more closely related to each other than to other major protostome taxa (e.g., molluscs, flatworms, brachio
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Molecular phylogeny of the Annelida
Canadian Journal of Zoology, 2000Co-Authors: Damhnait MchughAbstract:Traditionally, the Annelida has been classified as a group comprising the Polychaeta and the Clitellata. Recent phylogenetic analyses have led to profound changes in the view that the Annelida, as traditionally formulated, is a natural, monophyletic group. Both molecular and morphological analyses support placement of the Siboglinidae (formerly the Pogonophora) as a derived group within the Annelida; there is also evidence, based on molecular analysis of the nuclear gene elongation factor-1α, that the unsegmented echiurids are derived Annelids. While monophyly of the Clitellata is well-supported by both molecular and morphological analyses, there is no molecular evidence to support monophyly of the polychaete Annelids; the Clitellata fall within a paraphyletic polychaete grade. Relationships among groups of polychaete Annelids have not yet been resolved by molecular analysis. Within the Clitellata, paraphyly of the Oligochaeta was indicated in a phylogenetic analysis of cytochrome c oxidase I, which supported a sister relationship between the leeches, including an acanthobdellid and a branchiobdellid, and two of the four oligochaetes in the analysis. There is some evidence from analysis of 18S rRNA sequences for a sister-group relationship between the clitellates and the taxon Aeolosoma. There is no agreement regarding the body form of the basal Annelid, and while molecular analyses provide strong support for the Eutrochozoa, the identity of sister-group to the Annelida among the Eutrochozoa remains enigmatic. It is recommended that future investigations include additional conserved gene sequences and expanded taxon sampling. It is likely that the most productive approach to resolving Annelid phylogeny, and thus increasing our understanding of Annelid evolution, will come from combined analyses of several gene sequences.
Gunter Purschke - One of the best experts on this subject based on the ideXlab platform.
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Within-family plasticity of nervous system architecture in Syllidae (Annelida, Errantia)
Frontiers in Zoology, 2020Co-Authors: Hannah Schmidbaur, Gunter Purschke, Thomas Schwaha, Rico Franzkoch, Gerhard SteinerAbstract:Background The ground pattern underlying the nervous system of the last common ancestor in Annelids was long thought to be settled, consisting of a dorsal brain, circumoesophageal connectives and a subepithelial, ladder-like ventral nerve cord with segmental ganglia connected by paired connectives. With the advent of immunocytochemical stainings and confocal laser scanning microscopy, it becomes evident that its architecture is extremely diverse, which makes the reconstruction of a ground pattern in Annelida challenging. Whereas the nervous systems of many different families has already been described, only very few studies looked at the diversity of nervous systems within such clades to give a closer estimate on how plastic the Annelid nervous system really is. So far, little is known on syllid nervous system architecture, one of the largest and most diverse groups of marine Annelids. Results The position of the brain, the circumoesophageal connectives, the stomatogastric nervous system, the longitudinal nerves that traverse each segment and the innervation of appendages are relatively uniform within the clade. Both the number of connectives within the ventral nerve cord and the number of segmental nerves, which in earlier studies were used to infer phylogenetic relationships and to reconstruct an Annelid ground pattern, are highly diverse and differ between genera or even within a given genus. Differences in the distribution of somata of the brain, the nuchal innervation and its associated cell bodies were found between Syllinae and Exogoninae and may be subfamily-specific. Conclusions The nervous system morphology of syllids very likely depends on the taxon-specific ecological requirements. Thus, it is not surprising that in a clade, which occupies such diverse niches as the Annelida, we find similar patterns in phylogenetically widely separated species in similar niches and a high degree of modularity within a family. Only standardized protocols and staining methods can lead to comparable results, but so far different approaches have been taken to describe Annelid nervous systems, making homologization of certain structures difficult. This study provides the first thorough description of the nervous system in the family Syllidae, allowing more detailed comparisons between Annelid families in the future.
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The central nervous system of Oweniidae (Annelida) and its implications for the structure of the ancestral Annelid brain
Frontiers in zoology, 2019Co-Authors: Gunter Purschke, Pat Hutchings, Thomas BartolomaeusAbstract:Recent phylogenomic analyses congruently reveal a basal clade which consists of Oweniidae and Mageloniidae as sister group to the remaining Annelida. These results indicate that the last common ancestor of Annelida was a tube-dwelling organism. They also challenge traditional evolutionary hypotheses of different organ systems, among them the nervous system. In textbooks the central nervous system is described as consisting of a ganglionic ventral nervous system and a dorsally located brain with different tracts that connect certain parts of the brain to each other. Only limited information on the fine structure, however, is available for Oweniidae, which constitute the sister group (possibly together with Magelonidae) to all remaining Annelids. The brain of Oweniidae is ring- shaped and basiepidermal. Ganglia, higher brain centers or complex sensory organs do not exist; instead the central nervous system is medullary. Posterior to the brain the ventral medullary cord arises directly from the ventral region of the brain in Myriowenia sp. while in Owenia fusiformis two medullary cords arise perpendicular to the brain ring, extend caudally and fuse posterior. The central nervous system is composed of a central neuropil and surrounding somata of the neurons. According to ultrastructural and histological data only one type of neuron is present in the central nervous system. The central nervous system of Oweniidae is the simplest in terms of enlargement of the dorsal part of the brain and neuron distribution found among Annelida. Our investigation suggests that neither ganglia nor commissures inside the brain neuropil or clusters of polymorphic neurons were present in the Annelid stem species. These structures evolved later within Annelida, most likely in the stem lineage of Amphinomidae, Sipuncula and PleistoAnnelida. Palps were supposedly present in the last common ancestor of Annelids and innervated by two nerves originating in the dorsal part of the brain. A broader comparison with species of each major spiralian clade shows the medullary nervous system to be a common feature and thus possibly representing the ancestral state of the spiralian nervous system. Moreover, ganglia and clusters of polymorphic neurons seemingly evolved independently in the compared taxa of Spiralia and Annelida.
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The Evolution of Annelids Reveals Two Adaptive Routes to the Interstitial Realm
Current biology : CB, 2015Co-Authors: Torsten H. Struck, Anja Golombek, Wilfried Westheide, Gunter Purschke, Anne Weigert, Christoph Bleidorn, Franziska Anni Franke, Kenneth M. HalanychAbstract:Summary Many animals permanently inhabit the marine interstitium, the space between sand grains [1, 2]. Different evolutionary scenarios may explain the existence of interstitial animals [3, 4]. These scenarios include (1) that the interstitial realm is the ancestral habitat of bilaterians [5, 6], (2) that interstitial taxa evolved from larger ancestors by miniaturization, or (3) progenesis [3]. The first view mirrors the former hypothesis that interstitial Annelids, called archiAnnelids, were at the base of the Annelid radiation [7]. Based on morphological data, however, progenesis is generally favored for interstitial Annelids today [3, 4, 8]. Herein, our phylogenomic approach revealed that interstitial archiAnnelids are robustly placed into two groups nested within the Annelid tree. Evolution of the first group comprising among others Dinophilidae is best explained by progenesis. In contrast, the second group comprising Protodrilida and Polygordiidae appears to have evolved by stepwise miniaturization adapting from coarser to finer sediments. Thus, in addition to progenesis [3, 4], miniaturization, thought to be too slow for an adaptation to the interstitium [3], is an important second route allowing adaptation to interstitial environments. Both progenesis and miniaturization should be considered when investigating evolution of interstitial taxa [1, 3].
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illuminating the base of the Annelid tree using transcriptomics
Molecular Biology and Evolution, 2014Co-Authors: Matthias Meyer, Detlev Arendt, Kenneth M. Halanych, Birgit Nickel, Bernhard Hausdorf, Scott R Santos, Gunter PurschkeAbstract:Annelida is one of three animal groups possessing segmentation and is central in considerations about the evolution of different character traits. It has even been proposed that the bilaterian ancestor resembled an Annelid. However, a robust phylogeny of Annelida, especially with respect to the basal relationships, has been lacking. Our study based on transcriptomic data comprising 68,750-170,497 amino acid sites from 305 to 622 proteins resolves Annelid relationships, including Chaetopteridae, Amphinomidae, Sipuncula, Oweniidae, and Magelonidae in the basal part of the tree. Myzostomida, which have been indicated to belong to the basal radiation as well, are now found deeply nested within Annelida as sister group to Errantia in most analyses. On the basis of our reconstruction of a robust Annelid phylogeny, we show that the basal branching taxa include a huge variety of life styles such as tube dwelling and deposit feeding, endobenthic and burrowing, tubicolous and filter feeding, and errant and carnivorous forms. Ancestral character state reconstruction suggests that the ancestral Annelid possessed a pair of either sensory or grooved palps, bicellular eyes, biramous parapodia bearing simple chaeta, and lacked nuchal organs. Because the oldest fossil of Annelida is reported for Sipuncula (520 Ma), we infer that the early diversification of Annelids took place at least in the Lower Cambrian.
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Phylogenomic analyses unravel Annelid evolution
Nature, 2011Co-Authors: Torsten H. Struck, Achim Meyer, Bernhard Lieb, Christiane Paul, Natascha Hill, Stefanie Hartmann, Christoph Hösel, Michael Kube, Ralph Tiedemann, Gunter PurschkeAbstract:Annelida, the ringed worms, is a highly diverse animal phylum that includes more than 15,000 described species and constitutes the dominant benthic macrofauna from the intertidal zone down to the deep sea. A robust Annelid phylogeny would shape our understanding of animal body-plan evolution and shed light on the bilaterian ground pattern. Traditionally, Annelida has been split into two major groups: Clitellata (earthworms and leeches) and polychaetes (bristle worms), but recent evidence suggests that other taxa that were once considered to be separate phyla (Sipuncula, Echiura and Siboglinidae (also known as Pogonophora)) should be included in Annelida. However, the deep-level evolutionary relationships of Annelida are still poorly understood, and a robust reconstruction of Annelid evolutionary history is needed. Here we show that phylogenomic analyses of 34 Annelid taxa, using 47,953 amino acid positions, recovered a well-supported phylogeny with strong support for major splits. Our results recover chaetopterids, myzostomids and sipunculids in the basal part of the tree, although the position of Myzostomida remains uncertain owing to its long branch. The remaining taxa are split into two clades: Errantia (which includes the model Annelid Platynereis), and Sedentaria (which includes Clitellata). Ancestral character trait reconstructions indicate that these clades show adaptation to either an errant or a sedentary lifestyle, with alteration of accompanying morphological traits such as peristaltic movement, parapodia and sensory perception. Finally, life history characters in Annelida seem to be phylogenetically informative.
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The central nervous system of Oweniidae (Annelida) and its implications for the structure of the ancestral Annelid brain
Frontiers in zoology, 2019Co-Authors: Gunter Purschke, Pat Hutchings, Thomas BartolomaeusAbstract:Recent phylogenomic analyses congruently reveal a basal clade which consists of Oweniidae and Mageloniidae as sister group to the remaining Annelida. These results indicate that the last common ancestor of Annelida was a tube-dwelling organism. They also challenge traditional evolutionary hypotheses of different organ systems, among them the nervous system. In textbooks the central nervous system is described as consisting of a ganglionic ventral nervous system and a dorsally located brain with different tracts that connect certain parts of the brain to each other. Only limited information on the fine structure, however, is available for Oweniidae, which constitute the sister group (possibly together with Magelonidae) to all remaining Annelids. The brain of Oweniidae is ring- shaped and basiepidermal. Ganglia, higher brain centers or complex sensory organs do not exist; instead the central nervous system is medullary. Posterior to the brain the ventral medullary cord arises directly from the ventral region of the brain in Myriowenia sp. while in Owenia fusiformis two medullary cords arise perpendicular to the brain ring, extend caudally and fuse posterior. The central nervous system is composed of a central neuropil and surrounding somata of the neurons. According to ultrastructural and histological data only one type of neuron is present in the central nervous system. The central nervous system of Oweniidae is the simplest in terms of enlargement of the dorsal part of the brain and neuron distribution found among Annelida. Our investigation suggests that neither ganglia nor commissures inside the brain neuropil or clusters of polymorphic neurons were present in the Annelid stem species. These structures evolved later within Annelida, most likely in the stem lineage of Amphinomidae, Sipuncula and PleistoAnnelida. Palps were supposedly present in the last common ancestor of Annelids and innervated by two nerves originating in the dorsal part of the brain. A broader comparison with species of each major spiralian clade shows the medullary nervous system to be a common feature and thus possibly representing the ancestral state of the spiralian nervous system. Moreover, ganglia and clusters of polymorphic neurons seemingly evolved independently in the compared taxa of Spiralia and Annelida.
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The central nervous system of Oweniidae (Annelida) and its implications for the structure of the ancestral Annelid brain
Frontiers in Zoology, 2019Co-Authors: Pat Hutchings, Thomas BartolomaeusAbstract:Background Recent phylogenomic analyses congruently reveal a basal clade which consists of Oweniidae and Mageloniidae as sister group to the remaining Annelida. These results indicate that the last common ancestor of Annelida was a tube-dwelling organism. They also challenge traditional evolutionary hypotheses of different organ systems, among them the nervous system. In textbooks the central nervous system is described as consisting of a ganglionic ventral nervous system and a dorsally located brain with different tracts that connect certain parts of the brain to each other. Only limited information on the fine structure, however, is available for Oweniidae, which constitute the sister group (possibly together with Magelonidae) to all remaining Annelids. Results The brain of Oweniidae is ring- shaped and basiepidermal. Ganglia, higher brain centers or complex sensory organs do not exist; instead the central nervous system is medullary. Posterior to the brain the ventral medullary cord arises directly from the ventral region of the brain in Myriowenia sp. while in Owenia fusiformis two medullary cords arise perpendicular to the brain ring, extend caudally and fuse posterior. The central nervous system is composed of a central neuropil and surrounding somata of the neurons. According to ultrastructural and histological data only one type of neuron is present in the central nervous system. Conclusion The central nervous system of Oweniidae is the simplest in terms of enlargement of the dorsal part of the brain and neuron distribution found among Annelida. Our investigation suggests that neither ganglia nor commissures inside the brain neuropil or clusters of polymorphic neurons were present in the Annelid stem species. These structures evolved later within Annelida, most likely in the stem lineage of Amphinomidae, Sipuncula and PleistoAnnelida. Palps were supposedly present in the last common ancestor of Annelids and innervated by two nerves originating in the dorsal part of the brain. A broader comparison with species of each major spiralian clade shows the medullary nervous system to be a common feature and thus possibly representing the ancestral state of the spiralian nervous system. Moreover, ganglia and clusters of polymorphic neurons seemingly evolved independently in the compared taxa of Spiralia and Annelida.
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Convergent evolution of the ladder-like ventral nerve cord in Annelida
Frontiers in zoology, 2018Co-Authors: Conrad Helm, Torsten H. Struck, Thomas Bartolomaeus, Patrick Beckers, Stephan Drukewitz, Ioannis Kourtesis, Anne Weigert, GĂźnter Purschke, Katrine Worsaae, Christoph Bleidorn, Anne Weigert, Christoph BleidornAbstract:A median, segmented, Annelid nerve cord has repeatedly been compared to the arthropod and vertebrate nerve cords and became the most used textbook representation of the Annelid nervous system. Recent phylogenomic analyses, however, challenge the hypothesis that a subepidermal rope-ladder-like ventral nerve cord (VNC) composed of a paired serial chain of ganglia and somata-free connectives represents either a plesiomorphic or a typical condition in Annelids. Using a comparative approach by combining phylogenomic analyses with morphological methods (immunohistochemistry and CLSM, histology and TEM), we compiled a comprehensive dataset to reconstruct the evolution of the Annelid VNC. Our phylogenomic analyses generally support previous topologies. However, the so far hard-to-place Apistobranchidae and Psammodrilidae are now incorporated among the basally branching Annelids with high support. Based on this topology we reconstruct an intraepidermal VNC as the ancestral state in Annelida. Thus, a subepidermal ladder-like nerve cord clearly represents a derived condition. Based on the presented data, a ladder-like appearance of the ventral nerve cord evolved repeatedly, and independently of the transition from an intraepidermal to a subepidermal cord during Annelid evolution. Our investigations thereby propose an alternative set of neuroanatomical characteristics for the last common ancestor of Annelida or perhaps even Spiralia.
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Breaking the ladder: Evolution of the ventral nerve cord in Annelida
2018Co-Authors: Conrad Helm, Torsten H. Struck, Thomas Bartolomaeus, Patrick Beckers, Stephan Drukewitz, Ioannis Kourtesis, Anne Weigert, GĂźnter Purschke, Katrine Worsaae, Christoph Bleidorn, Anne Weigert, Christoph BleidornAbstract:A median, segmented, Annelid nerve cord has repeatedly been compared to the arthropod and vertebrate nerve cords and became the most used textbook representation of the Annelid nervous system. Recent phylogenomic analyses, however, challenge the hypothesis that a subepidermal rope-ladder-like ventral nerve cord (VNC) composed of a paired serial chain of ganglia and somata-free connectives represents neither a plesiomorphic nor a typical condition in Annelids. Using a comparative approach by combining phylogenomic analyses with morphological methods (immunohistochemistry and CLSM, histology and TEM), we compiled a comprehensive dataset to reconstruct the evolution of the Annelid VNC. Our phylogenomic analyses generally support previous topologies. However, the so far hard-to-place Apistobranchidae and Psammodrilidae are now incorporated among the basally branching Annelids with high support. Based on this topology we reconstruct an intraepidermal VNC as ancestral state in Annelida. Thus, a subepidermal ladder-like nerve cord clearly represents a derived condition. Based on the presented data, a ladder-like appearance of the ventral nerve cord evolved repeatedly, and independently of the transition from an intraepidermal to a subepidermal cord during Annelid evolution. Our investigations thereby question a common origin of the bilaterian median ganglionated VNC and propose an alternative set of neuroanatomical characteristics of the last common ancestor of Annelida or perhaps even Spiralia.
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Mitochondrial genome sequence and gene order of Sipunculus nudus give additional support for an inclusion of Sipuncula into Annelida
BMC genomics, 2009Co-Authors: Adina Mwinyi, Thomas Bartolomaeus, Achim Meyer, Bernhard Lieb, Lars PodsiadlowskiAbstract:Mitochondrial genomes are a valuable source of data for analysing phylogenetic relationships. Besides sequence information, mitochondrial gene order may add phylogenetically useful information, too. Sipuncula are unsegmented marine worms, traditionally placed in their own phylum. Recent molecular and morphological findings suggest a close affinity to the segmented Annelida. The first complete mitochondrial genome of a member of Sipuncula, Sipunculus nudus, is presented. All 37 genes characteristic for metazoan mtDNA were detected and are encoded on the same strand. The mitochondrial gene order (protein-coding and ribosomal RNA genes) resembles that of Annelids, but shows several derivations so far found only in Sipuncula. Sequence based phylogenetic analysis of mitochondrial protein-coding genes results in significant bootstrap support for Annelida sensu lato, combining Annelida together with Sipuncula, Echiura, Pogonophora and Myzostomida. The mitochondrial sequence data support a close relationship of Annelida and Sipuncula. Also the most parsimonious explanation of changes in gene order favours a derivation from the Annelid gene order. These results complement findings from recent phylogenetic analyses of nuclear encoded genes as well as a report of a segmental neural patterning in Sipuncula.