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Using Phylogenetic Analysis to Investigate Eukaryotic Gene Origin
Published on: August 14, 2018
Phylogenetic position of Nemertea derived from phylogenomic data
Torsten H Struck1, Frauke Fisse
1FB05 Biology/Chemistry, AG Zoology, University of Osnabrück, Osnabrück, Germany. struck@biologie.uni-osnabrueck.de
Molecular Biology and Evolution
|January 29, 2008
Summary
Phylogenomic analysis reveals Nemertea (ribbon worms) are not closely related to Platyhelminthes (flatworms). Instead, Nemertea group with Annelida and Mollusca, indicating independent evolution of acoelomy in these lineages.
Area of Science:
- * Zoology
- * Evolutionary Biology
- * Phylogenetics
Background:
- * Nemertea and Platyhelminthes traditionally grouped as acoelomates, with Nemertea sometimes considered sister to coelomate Protostomia.
- * Previous molecular data only rejected a sister group relationship to Teloblastica (Neotrochozoa plus Arthropoda).
- * Phylogenomic data were lacking for Nemertea, hindering robust phylogenetic placement.
Purpose of the Study:
- * To determine the phylogenetic position of Nemertea using phylogenomic data.
- * To test hypotheses regarding the evolutionary relationships between Nemertea, Platyhelminthes, and other major bilaterian groups.
- * To investigate the evolution of acoelomy and larval homologies.
Main Methods:
- * Expressed sequence tag data collected from Lineus viridis.
- * Combined data with existing sequences to create a dataset of 9,377 amino acid positions from 60 ribosomal proteins.
- * Performed Maximum Likelihood analyses and Bayesian inferences.
Main Results:
- * Phylogenomic analyses consistently placed Nemertea within a clade alongside Annelida and Mollusca.
- * Hypothesis testing significantly rejected sister group relationships between Nemertea and Platyhelminthes, or Nemertea and Teloblastica.
- * The Coelomata hypothesis was not supported; acoelous organization evolved independently in Nemertea and Platyhelminthes.
Conclusions:
- * Nemertea are evolutionarily distinct from Platyhelminthes, with acoelomy likely arising from secondary coelom reduction in Nemertea.
- * Larval forms (Götte's, Müller's, and pilidium) are not homologous, refuting the Parenchymia hypothesis.
- * Results support convergent evolution of segmentation in Annelida and Arthropoda.
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