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Reconstructing ordinal relationships in the Demospongiae using mitochondrial genomic data.

Dennis V Lavrov1, Xiujuan Wang, Michelle Kelly

  • 1Department of Ecology, Evolution, and Organismal Biology, Iowa State University, 343A Bessey Hall, Ames, IA 50011, USA. dlavrov@iastate.edu

Molecular Phylogenetics and Evolution
|June 28, 2008
PubMed
Summary

This study resolves demosponge (phylum Porifera) phylogeny using mitochondrial genomes, revealing five major clades and their relationships. Findings challenge traditional classifications and highlight the utility of mitochondrial gene arrangements for evolutionary studies.

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Area of Science:

  • Marine Biology
  • Evolutionary Biology
  • Genomics

Background:

  • The class Demospongiae, comprising most sponge diversity, has unresolved higher-level phylogenetic relationships.
  • Lack of a resolved phylogeny hinders studies on demosponge biology, evolution, and biodiversity, impacting conservation efforts.
  • Previous phylogenetic analyses have faced challenges due to limited data and complex evolutionary histories within Demospongiae.

Purpose of the Study:

  • To investigate the phylogenetic relationships among the 14 recognized orders within the class Demospongiae.
  • To resolve fundamental questions regarding the monophyly of Demospongiae and the interrelationships of its major lineages.
  • To evaluate the congruence between mitochondrial DNA (mtDNA)-based and nuclear ribosomal RNA (rRNA)-based phylogenies.

Main Methods:

  • Assembled a comprehensive mitochondrial genomic dataset including 17 new and 5 previously published complete demosponge mitochondrial genomes, covering all recognized orders.
  • Determined and analyzed 18S rRNA sequences for the same set of species to compare phylogenies derived from different genomic sources.
  • Analyzed mitochondrial gene arrangements to assess their utility in inferring order-level relationships within Demospongiae.

Main Results:

  • Strong support was found for five major clades within Demospongiae: Homoscleromorpha (G0), Keratosa (G1), Myxospongiae (G2), marine Haplosclerida (G3), and the remaining demosponges (G4).
  • The study established the phylogenetic relationships among these clades as (G0((G1+G2)(G3+G4))).
  • Mitochondrial genomic data did not support the monophyly of traditional subclasses (Ceractinomorpha, Tetractinomorpha) or several existing orders; mitochondrial gene arrangements proved informative for phylogenetic inference.

Conclusions:

  • The proposed five-clade system and their interrelationships provide a robust framework for understanding demosponge evolution.
  • The findings necessitate a re-evaluation of current taxonomic classifications within Demospongiae, particularly concerning traditional subclasses and certain orders.
  • Mitochondrial gene order analysis offers a valuable complementary method for resolving phylogenetic relationships, especially in groups with frequent gene rearrangements.