Journal of Molecular Evolution

, Volume 71, Issue 2, pp 153–167 | Cite as

Accelerated Evolutionary Rate of Housekeeping Genes in Tunicates

  • Georgia Tsagkogeorga
  • Xavier Turon
  • Nicolas Galtier
  • Emmanuel J. P. Douzery
  • Frédéric Delsuc


Phylogenomics has recently revealed that tunicates represent the sister-group of vertebrates in the newly defined clade Olfactores. However, phylogenomic and comparative genomic studies have also suggested that tunicates are characterized by an elevated rate of molecular evolution and a high degree of genomic divergence. Despite the recurrent interest in the group, the picture of tunicate peculiar evolutionary dynamics is still fragmentary, as it mainly lies in studies focusing on only a few model species. In order to expand the available genomic data for the group, we used the high-throughput 454 technology to sequence the partial transcriptome of a previously unsampled tunicate, Microcosmus squamiger. This allowed us to get further insights into tunicate-accelerated evolution through a comparative analysis based on pertinent phylogenetic markers, i.e., a core of 35 housekeeping genes conserved across bilaterians. Our results showed that tunicates evolved on average about two times faster than the other chordates, yet the degree of this acceleration varied extensively upon genes and upon lineages. Appendicularia and Aplousobranchia were detected as the most divergent groups which were also characterized by highly heterogeneous substitution rates across genes. Finally, an estimation of the dN/dS ratio in three pairs of closely related taxa within Olfactores did not reveal strong differences between the tunicate and vertebrate lineages suggesting that for this set of housekeeping genes, the accelerated evolution of tunicates is plausibly due to an elevated mutation rate rather than to particular selective effects.


Urochordates Chordates Phylogenomics 454 sequencing Molecular evolution Evolutionary rate Microcosmus squamiger Oikopleura dioica 

Supplementary material

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Copyright information

© Springer Science+Business Media, LLC 2010

Authors and Affiliations

  • Georgia Tsagkogeorga
    • 1
  • Xavier Turon
    • 2
  • Nicolas Galtier
    • 1
  • Emmanuel J. P. Douzery
    • 1
  • Frédéric Delsuc
    • 1
  1. 1.Université Montpellier 2 and CNRS, Institut des Sciences de l’Evolution (UMR 5554)Montpellier Cedex 05France
  2. 2.Centre d’Estudis Avançats de Blanes (CEAB, CSIC), Accés Cala S. Francesc 14Blanes (Girona)Spain

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