Animal phylogeny in the light of the trochaea theory

Nielsen, Claus

doi:10.1111/j.1095-8312.1985.tb00396.x

Cited by 128 publications

(89 citation statements)

References 117 publications

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“…Indeed Ectoprocta and Entoprocta remain strongly united (bootstrap support 72%, Bayesian posterior probability 0.99). This agrees with the hypothesis that Bryozoa sensu lato is monophyletic ( Nielsen 1971( Nielsen , 1985( Nielsen , 2001Cavalier-Smith 1998). Alternative hypotheses concerning the phylogenetic position of ectoprocts, namely that they are sister to all other Lophotrochozoa including Platyzoa, i.e.…”

Section: (B) Relationships Of Lophophorates Within Lophotrochozoasupporting

confidence: 87%

Phylogenomic analyses of lophophorates (brachiopods, phoronids and bryozoans) confirm the Lophotrochozoa concept

2008

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Based on embryological and morphological evidence, Lophophorata was long considered to be the sister or paraphyletic stem group of Deuterostomia. By contrast, molecular data have consistently indicated that the three lophophorate lineages, Ectoprocta, Brachiopoda and Phoronida, are more closely related to trochozoans (annelids, molluscs and related groups) than to deuterostomes. For this reason, the lophophorate groups and Trochozoa were united to Lophotrochozoa. However, the relationships of the lophophorate lineages within Lophotrochozoa are still largely unresolved. Maximum-likelihood and Bayesian analyses were performed based on a dataset comprising 11 445 amino acid positions derived from 79 ribosomal proteins of 39 metazoan taxa including new sequences obtained from a brachiopod and a phoronid. These analyses show that the three lophophorate lineages are affiliated with trochozoan rather than deuterostome phyla. All hypotheses claiming that they are more closely related to Deuterostomia than to Protostomia can be rejected by topology testing. Monophyly of lophophorates was not recovered but that of Bryozoa including Ectoprocta and Entoprocta and monophyly of Brachiozoa including Brachiopoda and Phoronida were strongly supported. Alternative hypotheses that are refuted include (i) Brachiozoa as the sister group of Mollusca, (ii) ectoprocts as sister to all other Lophotrochozoa including Platyzoa, and (iii) ectoprocts as sister or to all other protostomes except chaetognaths.

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Section: (B) Relationships Of Lophophorates Within Lophotrochozoasupporting

confidence: 87%

Phylogenomic analyses of lophophorates (brachiopods, phoronids and bryozoans) confirm the Lophotrochozoa concept

2008

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“…There are two modern versions of this hypothesis, the trochaea theory of Nielsen and Nrrevang (1985); Nielsen (1985Nielsen ( , 1987Nielsen ( , 1995Nielsen ( , 1998Nielsen ( , 2000, and the set-aside cell hypothesis of Davidson and colleagues (Davidson et al 1995;Peterson et al 1997Peterson et al , 2000aCameron et al 1998). Although the set-aside hypothesis was formulated independently of any ecological considerations, and made no explicit ecological predictions, the trochaea theory of Nielsen did consider some of the initial ecological drivers.…”

Section: Introductionmentioning

confidence: 99%

Molecular paleoecology: using gene regulatory analysis to address the origins of complex life cycles in the late Precambrian

Dunn

Moy

Angerer

et al. 2007

Evolution and Development

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SUMMARY Molecular paleoecology is the application of molecular data to test hypotheses made by paleoecological scenarios. Here, we use gene regulatory analysis to test between two competing paleoecological scenarios put forth to explain the evolution of complex life cycles. The first posits that early bilaterians were holobenthic, and the evolution of macrophagous grazing drove the exploitation of the pelagos by metazoan eggs and embryos, and eventually larvae. The alternative hypothesis predicts that early bilaterians were holopelagic, and new adult stages were added on when these holopelagic forms began to feed on the benthos. The former hypothesis predicts that the larvae of protostomes and deuterostomes are not homologous, with the implication that larval-specific structures, including the apical organ, are the products of convergent evolution, whereas the latter hypothesis predicts homology of larvae, specifically homology of the apical organ. We show that in the sea urchin, Strongylocentrotus purpuratus, the transcription factors NK2.1 and HNF6 are necessary for the correct spatial expression profiles of five different cilia genes. All of these genes are expressed exclusively in the apical plate after the mesenchyme-blastula stage in cells that also express NK2.1 and HNF6. In addition, abrogation of SpNK2.1 results in embryos that lack the apical tuft. However, in the red abalone, Haliotis rufescens, NK2.1 and HNF6 are not expressed in any cells that also express these same five cilia genes. Nonetheless, like the sea urchin, the gastropod expresses both NK2.1 and FoxA around the stomodeum and foregut, and FoxA around the proctodeum. As we detected no similarity in the development of the apical tuft between the sea urchin and the abalone, these molecular data are consistent with the hypothesis that the evolution of mobile, macrophagous metazoans drove the evolution of complex life cycles multiple times independently in the late Precambrian.

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“…Although long considered basal bilaterians owing to their lack of advanced metazoan characteristics such as a body cavity or a through gut with separate mouth and anus (e.g. Hyman (1951), although see Nielsen (1985) for an alternative morphological viewpoint), molecular studies have instead robustly linked the Rhabditophora and the closely related Catenulida to the eutrochozoan phyla such as Mollusca and Annelida, suggesting that their morphological simplicity is a secondarily derived state (Tyler 2001). For clarity we refer to the rhabditophoran 1 catenulid clade as the Platyhelminthes.…”

Section: Introductionmentioning

confidence: 99%

Combined large and small subunit ribosomal RNA phylogenies support a basal position of the acoelomorph flatworms

Telford

Lockyer

CartwrightFinch

et al. 2003

Proc. R. Soc. Lond. B

146

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The phylogenetic position of the phylum Platyhelminthes has been re-evaluated in the past decade by analysis of diverse molecular datasets. The consensus is that the Rhabditophora 1 Catenulida, which includes most of the flatworm taxa, are not primitively simple basal bilaterians but are related to coelomate phyla such as molluscs. The status of two other groups of acoelomate worms, Acoela and Nemertodermatida, is less clear. Although many characteristics unite these two groups, initial molecular phylogenetic studies placed the Nemertodermatida within the Rhabditophora, but placed the Acoela at the base of the Bilateria, distant from other flatworms. This contradiction resulted in scepticism about the basal position of acoels and led to calls for further data. We have sequenced large subunit ribosomal RNA genes from 13 rhabditophorans 1 catenulids, three acoels and one nemertodermatid, tripling the available data. Our analyses strongly support a basal position of both acoels and nemertodermatids. Alternative hypotheses are significantly less well supported by the data. We conclude that the Nemertodermatida and Acoela are basal bilaterians and, owing to their unique body plan and embryogenesis, should be recognized as a separate phylum, the Acoelomorpha.

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Animal phylogeny in the light of the trochaea theory

Cited by 128 publications

References 117 publications

Phylogenomic analyses of lophophorates (brachiopods, phoronids and bryozoans) confirm the Lophotrochozoa concept

Phylogenomic analyses of lophophorates (brachiopods, phoronids and bryozoans) confirm the Lophotrochozoa concept

Molecular paleoecology: using gene regulatory analysis to address the origins of complex life cycles in the late Precambrian

Combined large and small subunit ribosomal RNA phylogenies support a basal position of the acoelomorph flatworms

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